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Liquid-membrane phenomena in imipramine action
Liquid-Membrane Phenomena in Imipramine Action R. C. SRIVASTAVA, R. P. S. JAKHAR, AND S. B. BHISE Birla Institute o f Technology and Science, Pilani-333031, Rajasthan, India Received July 2, 1981; accepted September 4, 1981 Modification in the transport of biogenic amines and cations in p r e s e n c e of imipramine was studied. T h e liquid m e m b r a n e generated by imipramine, which is a tricyclic antidepressant drug and is surface active in nature, was s h o w n to contribute to the m e c h a n i s m o f its action.
the imipramine liquid membrane in series with the supporting membrane has been studied in order to gain information on the contribution of the liquid membrane in the action of the drug. In these experiments a cellulose acetate microfiltration membrane/aqueous interface has been deliberately chosen so that the specific interaction of the drug with the components of the biological membranes as a cause for the modification in the permeabilities of biogenic amines and cations is ruled out and data on passive transport alone are obtained.
INTRODUCTION
According to Kesting's hypothesis (1-3) a surface-active substance when added to water or aqueous solutions generates a liquid membrane which completely covers the interface at concentrations equal to or higher than its critical micelle concentration (CMC) and modifies the flow of permeants across the interface. Since a large number of surface-active drugs (4) are known to affect the transport of biologically important molecules, it is tempting to assess the contribution of liquid-membrane phenomena in the mechanism of action of such drugs. Tricyclic antidepressant drugs like imipramine are known to be surface active in nature (4, 5). Explanation of the antidepressant action is based on the fact that these drugs reduce the uptake of catecholamines in the nervous tissue (6). Palm et al. (7), while investigating the action of drugs like, reserpine, prenylamine, chlorpromazine, propranalol, etc., which inhibit catecholamine transport, have concluded that "irrespective of chemical structure, the surface activity of psychotropic drugs mainly determines their potency to affect all kinds of membranes especially that of catecholamine storing particles." In the present paper existence of a liquid membrane generated by imipramine at the interface has been demonstrated. The transport of biogenic amines and cations through
EXPERIMENTAL
Materials
Imipramine hydrochloride (B. P. Jagson Pal & Co.); dopamine chlorhydrate (Loba Chemie); adrenaline hydrogen tartrate (Loba Chemie); L-noradrenaline (Fluka A. G.); 5-hydroxytryptamine creatinine sulphate (Koch Light Laboratories Ltd.); sodium, potassium, and calcium chlorides (all Analar grades) and distilled water, distilled once over potassium permanganate in an allPyrex glass still were used in the present experiments. Methods
The critical micelle concentration (CMC) of aqueous imipramine hydrochloride solution was determined from the plots of sur56
0021-9797/82/050056-06502.00/0 Copyright © 1982by AcademicPress, Inc. All rights of reproductiofi in any form reserved.
Journal of Colloidand Interface Science, Vol. 87, No. 1, May 1982
57
LIQUID-MEMBRANE PHENOMENA
face tension against concentration. The surface tensions were measured using a Fisher Tensiomat model 21. The CMC value for aqueous solution of imipramine hydrochloride was found to be 1.48 × 10-4 M. The all-glass cell described earlier (8) was used for the transport studies. The transport cell was separated into two compartments, C and D, of volumes 250 and 7.0 ml, respectively, by a Sartorious cellulose acetate microfiltration membrane (Cat. No. 11107) of thickness ! x 10-4m and area 5.373 × 10-5 m z, which acted as a support for the liquid membrane. For measurements of hydraulic permeability, aqueous solutions of imipramine hydrochloride of various concentrations were filled in compartment C of the transport cell while compartment D was filled with distilled water. The concentration ranges chosen were such that we obtain data on both the lower and the higher sides of the CMC. Known pressures were applied on compartment C by adjusting the pressure head and the consequent volume flux was measured by noting the rate of advancement of liquid meniscus in the capillary with a cathetometer of least count 0.001 cm and a stopwatch reading up to 0.1 sec. Magnitude of the applied pressure was also measured by noting the position of pressure head with the cathetometer. During the volume flux measurements, the solution in compartment C (Fig. 1, Ref. (8)) was well stirred and the electrodes E1 and E2 were electrically short-circuited. For the measurement of permeability of biogenic amines and cations, two sets of experiments were performed. In the first set of experiments, compartment C of the transport cell was filled with the solutions of respective permeants, prepared in 5.92 × 10-4 M solution of imipramine hydrochloride and compartment D was filled with distilled water. In the second set of experiments compartment D was filled with 5.92 x 10-4 M solution of imipramine hydrochloride and compartment C was filled with
aqueous solution of known concentration of the permeants. In the control experiment, however, no imipramine hydrochloride was used. The initially chosen concentrations of biogenic amines and of cations were comparable to their concentrations in the vicinity of nervous tissue. The condition of no net volume flux (Jv = 0) was imposed on the system by adjusting the pressure head, so that the liquid meniscus in the capillary remained stationary. After a known period of time the concentration of the permeant in another compartment was measured. The amount of permeant gained by compartment D divided by the time and the area of the membrane gave the value of solute flux (Js). The value of solute permeability w was estimated using the definition (9, 10)
(J-iL-)
= to,
[1]
Jv=0
where ~ c is the osmotic pressure difference. The value of ~ v used in the calculations of co was the average of the values of ~ v at the beginning of the experiment (t = 0) and at the end of the experiment. During the permeability measurements, the solution in compartment C was kept well stirred. All measurements were made at constant temperature by placing the transport cell in a thermostat set at 37 _ 0. I°C. Estimations. The amounts of the various permeants transported in compartment D were estimated as follows. Biogenic amines. Imipramine was observed to quench the fluorescence intensity of biogenic amines by inner filter effect; hence the biogenic amines were not estimated by measuring the fluorescence intensity. The absorption maxima for the biogenic amines lies around 275 nm. Hence for the estimation of the amount of biogenic amines transported in compartment D a calibration curve of absorbance versus concentrations of the biogenic amines was constructed using a mixture of constant amount of imipJournal of Colloid and lnterface Science, Vol. 87, No. 1, May 1982
58
SRIVASTAVA, J A K H A R , A N D B H I S E
ramine hydrochloride and varying amounts of the biogenic amines. The same amount of imipramine hydrochloride was added to the solution of compartment D in case of the control and the first set of experiments. The absorbance at 275 nm for this mixture was recorded and from the calibration curve the amount of the transported biogenic amine was computed. In case of second set of the experiments, where imipramine hydrochloride was already in compartment D, no fresh imipramine hydrochloride was added. The mixture of imipramine hydro-
chloride and the biogenic amines were observed to obey Beer's law. Cations. The amounts of sodium, potassium, and calcium ions were determined using an atomic absorption spectrophotometer (Perkin-Elmer model 306). RESULTS AND DISCUSSION
From the hydraulic permeability data at various concentrations of imipramine hydrochloride (Fig. 1), it is obvious that the linear relationship
"1"
4.0
3.0 E O x >
2.0
1.0
0 0
~,.0
I~.0
12.0
16.0
-2 AP X 102--" Nm FIG. 1. The hydraulic permeability data. Curves I to VI are for the case when compartment C was filled with imipramine solutions and compartment D with water. Imipramine concentration for O = 0, A = 0 . 1 4 8 x 10-4M, [] = 0 . 3 7 × 10-4M, • = 0 . 7 4 × 10-4M, • = 1.11 × 10-4M, ® = 1.48 × 10- 4 M , V = 3.70 × 10- 4 M , • = 7.40 × 10- 4 M . Journal of Colloid and Interface Science, Vol. 87, No. 1, May 1982
59
LIQUID-MEMBRANE PHENOMENA
Jv = L e ' A P ,
[2]
where Jv represents the volume flux per unit area of the membrane, AP the applied pressure difference, and Lp, the hydraulic conductivity coefficient, is obeyed in all cases. The values of Lp estimated from the slopes of the curves in Fig. 1 show a progressive decrease as the concentration of imipramine hydrochloride is increased (Table I). The decreasing trend continues up to the CMC, i.e., 1.48 × 10-4 M. When the concentration of imipramine hydrochloride is increased further the value of Le also decreases but this decrease is much less pronounced than the decrease noticed up to the CMC. This trend is in keeping with Kesting's liquid-membrane hypothesis (1-3) according to which as concentration of the surface-active substance is increased the supporting membrane get s progressively covered with the surfactant layer liquid membrane and at the CMC the coverage is complete. The slight decrease in the values of Lp beyond the value of CMC might be due to an increase in density of the liquid membrane as postulated by Kesting et al. (3). Analysis of the flow data (Fig. 1, Table I) in the light of mosaic-membrane model (11-13) further supports the existence of the liquid membrane in series with the supporting membrane. Following the arguments given earlier (8, 14) it can be shown that if the concentration of the surfactant is n times the CMC, n being less than or equal to I, the value of Le would be equal
to {(1 - n)L~ + nL~}, where L~o and L~ respectively represent the values of the hydraulic conductivity coefficient for the bare supporting membrane and the supporting membrane covered with the surfactant layer liquid membrane. Functionally L~, and L~ would be the values of Lp at 0 and the CMC of the surfactant. The values of Lp thus computed for 0.1, 0.25, 0.5, and 0.75 CMC of imipramine are given in Table I. These are in good agreement with the experimentally determined values. The value of co for biogenic amines and cations are recorded in Table II. In order to ensure that the supporting membrane of the transport cell is completely covered with the liquid membrane, the concentration of imipramine hydrochloride chosen for the present experiment was 5.92 × 10-4M which is much higher than its CMC. Since imipramine is surface active in nature, it has both hydrophobic and hydrophilic parts in its structure. The orientation of its molecule will, therefore, be significant when it forms a liquid membrane. The hydrophobic ends of imipramine molecules will be preferentially oriented toward the hydrophobic supporting membrane and their hydrophilic ends will face outward away from it. When imipramine is in compartment C of the transport cell (first set of experiments) the liquid membrane will present a polar surface to the permeants which are present in the same compartment. In the second set of experiments, however, where imipramine is in compartment D of the transport cell and the aqueous solution of the permeant in corn-
TABLE I Values of Le at Various Concentration of Irnipramine Conch. of imipramine (×104 M )
0
0.148 (0.1 C M C )
0.37 (0.25 C M C )
0.74 (0.5 C M C )
1.11 (0.75 C M C )
1.48 (CMC)
Le~ × 10s (m 3 see -~ N -E)
3.369 + 0.05
3.233 _+ 0.09
3.075 ,+ 0.08
2.925 -+ 0.06
2.702 .+ 0.07
2.451 ,+ 0.05
2.444 + 0.07
2.442 -+ 0.08
L~b × l 0 s (m 3 see -I N -I)
--
3.277 .+ 0.05
3.152 + 0.018
2.935 ,+ 0.03
2.718 + 0.041
--
--
--
3.70
7.40
° Experimental values. b Calculated values using mosaic model.
Journal o f Colloid and Interface Science, Vol. 87, No. 1, M a y 1982
60
SRIVASTAVA, JAKHAR, AND BHISE T A B L E II Solute Permeability w of Biogenic Amines and Cations in Presence of 5.92 × 10 -4 M Imipramine
Dopamine Noradrenaline Adrenaline 5-Hydroxytryptamine Sodium (chloride) Potassium (chloride) Calcium (chloride)
Wl (moles N - ' see -1)
~o2 (moles N -~ sec -~)
603 (moles N -t sec -1)
2.657 9.893 4.625 2.272 0.862 4.757 0.566
1.048 4.820 1.768 0.973 0.469 1.383 0.102
4.337 1.210 6.887 9.541 0.712 1.861 0.208
× × × X × X ×
10 -l° 10 -11 10 -1° 10 -1° 10 -~° 10 -1° 10 -t°
X X × × × X ×
10 -l° 10 -11 10 -1° 10 -1° 10 -~° 10 -1° 10 -1°
× × × X × × ×
10 -1° 10 -9 10 -1° 10 -1° 10 -~° 10 -1° 10 -1°
Note. Wl--Control value when no imipramine was used. ¢o2--Imipramine in c o m p a r t m e n t D of the transport cell. o~s--Imipramine in c o m p a r t m e n t C of the transport cell.
partment C, the imipramine liquid membrane would present a hydrophobic surface to the permeant. The orientation of imipramine molecules with respect to approaching permeant would thus be different in the two sets of experiments. The values of oJ recorded in Table II indicate that in the first set of experiments, where the imipramine liquid membrane presents a hydrophilic surface to the permeants, the permeability of biogenic amines is increased. In the second set of experiments, however, where the imipramine liquid membrane presents a hydrophobic surface to the approaching permeant, a marked decrease in the permeability of biogenic amines is observed. Since in vivo imipramine is known to act by reducing the uptake of biogenic amines (6) the present study indicates that the specific orientation of imipramine with hydrophobic ends facing the permeants would also be necessary in the vicinity of nerve terminals. This reduction in the passive transport of biogenic amines and cations (Table II) is also likely to be accompanied by a consequent reduction in their active transport because access of the permeants to the active site located on the nerve membrane is likely to be effectively reduced due to the resistance offered by the liquid membrane interposed in between. Thus although neuronal uptake of biogenic amines is by active process (15) Journal of Colloid and Interface Science, Vol. 87, No. 1, M a y 1982
the formation of liquid membrane by imipramine seems to have a contribution in the mechanism of its action. In certain tissues imipramine is known to increase outflow of noradrenaline (15, 16). This may be because of the specific orientation of imipramine with its hydrophilic ends facing the catecholamines. Presumably even on adrenoceptors similar orientation of imipramine may be necessary. However, more understanding in terms of orientation of imipramine molecule with respect to the relevant biological membrane is necessary. The reduced permeability to cations in both orientations of imipramine can be explained on the basis of hydrophilicity of the ions. This observation may have relevance to the effect of imipramine on nerve conduction. ACKNOWLEDGMENT T h a n k s are due to the D e p a r t m e n t of Science and T e c h n o l o g y , N e w Delhi for financial support. REFERENCES 1. Kesting, R., Vincent, A., and Eberlin, J., O S W R & D Report No. 117, Aug. 1964. 2. Kesting, R. " R e v e r s e O s m o s i s Process U s i n g Surfactant Feed A d d i t i v e s , " O S W , Patent application S A L 830, Nov. 3, 1965. 3. Kesting, R., S u b c a s k y , W. J., and Paton, J. D., J. Colloid Interface Sci. 28, 156 (1968). 4. Felmeister, A., J. Pharm. Sci. 61, 151 (1972).
LIQUID-MEMBRANE PHENOMENA 5. Seeman, P., and Bialy, H. S., Biochem. Pharmacol. 12, 1181 (1963). 6. Shore, P. A.,Ann. Rev. Pharmacol. 12,209 (1972). 7. Palm, D., Grobecker, H., and Bak, I. J., in "New Aspects of Storage and Release Mechanisms of Catecholamines" (H. J. Shumann and G. Kroneberg, Eds.), pp. 188-198. Bayer Symposium II, Springer-Verlag, 1970. 8. Srivastava, R. C., and Jakhar, R. P. S., J. Phys. Chem. 85, 1457 (1981). 9. Katchalsky, A., and Curran, P. F., "Nonequilibrium Thermodynamics in Biophysics." Harvard Univ. Press, Cambridge, Mass., 1967. 10. Katchalsky, A., and Kedem, O., Biophys. J. 2, 53 (1962). 11. Spiegler, K. S., and Kedem, O., Desalination 1, 311 (1966).
61
12. Sherwood, T. K., Brain, P. L. T., and Fischer, R. E., Ind. Eng. Chem. Fundam. 6, 2 (1967). 13. Harris, F. L., Humphreys, G. B., and Spiegler, K. S., in "Membrane Separation Processes" (P. Meares, Ed.), Chap. 4. Elsevier, Amsterdam/New York, 1976. 14. Srivastava, R. C., and Yadav, Saroj, J. Colloid Interface Sci. 69, 280 (1979). 15. Iversen, L. L., in "Drugs and Transport Processes" (B. A. Collingham, Ed.), pp. 275-286. Macmillan, New York, 1974. 16. Glowinski, J., in "New Aspects of Storage and Release Mechanisms of Catecholamines" (H. J. Shumann and G. Kroneberg Eds.), pp. 237248. Bayer Symposium II, Springer-Verlag, 1970.
Journal of Colloid and Interface Science, Vol. 87, No. 1, May 1982
the imipramine liquid membrane in series with the supporting membrane has been studied in order to gain information on the contribution of the liquid membrane in the action of the drug. In these experiments a cellulose acetate microfiltration membrane/aqueous interface has been deliberately chosen so that the specific interaction of the drug with the components of the biological membranes as a cause for the modification in the permeabilities of biogenic amines and cations is ruled out and data on passive transport alone are obtained.
INTRODUCTION
According to Kesting's hypothesis (1-3) a surface-active substance when added to water or aqueous solutions generates a liquid membrane which completely covers the interface at concentrations equal to or higher than its critical micelle concentration (CMC) and modifies the flow of permeants across the interface. Since a large number of surface-active drugs (4) are known to affect the transport of biologically important molecules, it is tempting to assess the contribution of liquid-membrane phenomena in the mechanism of action of such drugs. Tricyclic antidepressant drugs like imipramine are known to be surface active in nature (4, 5). Explanation of the antidepressant action is based on the fact that these drugs reduce the uptake of catecholamines in the nervous tissue (6). Palm et al. (7), while investigating the action of drugs like, reserpine, prenylamine, chlorpromazine, propranalol, etc., which inhibit catecholamine transport, have concluded that "irrespective of chemical structure, the surface activity of psychotropic drugs mainly determines their potency to affect all kinds of membranes especially that of catecholamine storing particles." In the present paper existence of a liquid membrane generated by imipramine at the interface has been demonstrated. The transport of biogenic amines and cations through
EXPERIMENTAL
Materials
Imipramine hydrochloride (B. P. Jagson Pal & Co.); dopamine chlorhydrate (Loba Chemie); adrenaline hydrogen tartrate (Loba Chemie); L-noradrenaline (Fluka A. G.); 5-hydroxytryptamine creatinine sulphate (Koch Light Laboratories Ltd.); sodium, potassium, and calcium chlorides (all Analar grades) and distilled water, distilled once over potassium permanganate in an allPyrex glass still were used in the present experiments. Methods
The critical micelle concentration (CMC) of aqueous imipramine hydrochloride solution was determined from the plots of sur56
0021-9797/82/050056-06502.00/0 Copyright © 1982by AcademicPress, Inc. All rights of reproductiofi in any form reserved.
Journal of Colloidand Interface Science, Vol. 87, No. 1, May 1982
57
LIQUID-MEMBRANE PHENOMENA
face tension against concentration. The surface tensions were measured using a Fisher Tensiomat model 21. The CMC value for aqueous solution of imipramine hydrochloride was found to be 1.48 × 10-4 M. The all-glass cell described earlier (8) was used for the transport studies. The transport cell was separated into two compartments, C and D, of volumes 250 and 7.0 ml, respectively, by a Sartorious cellulose acetate microfiltration membrane (Cat. No. 11107) of thickness ! x 10-4m and area 5.373 × 10-5 m z, which acted as a support for the liquid membrane. For measurements of hydraulic permeability, aqueous solutions of imipramine hydrochloride of various concentrations were filled in compartment C of the transport cell while compartment D was filled with distilled water. The concentration ranges chosen were such that we obtain data on both the lower and the higher sides of the CMC. Known pressures were applied on compartment C by adjusting the pressure head and the consequent volume flux was measured by noting the rate of advancement of liquid meniscus in the capillary with a cathetometer of least count 0.001 cm and a stopwatch reading up to 0.1 sec. Magnitude of the applied pressure was also measured by noting the position of pressure head with the cathetometer. During the volume flux measurements, the solution in compartment C (Fig. 1, Ref. (8)) was well stirred and the electrodes E1 and E2 were electrically short-circuited. For the measurement of permeability of biogenic amines and cations, two sets of experiments were performed. In the first set of experiments, compartment C of the transport cell was filled with the solutions of respective permeants, prepared in 5.92 × 10-4 M solution of imipramine hydrochloride and compartment D was filled with distilled water. In the second set of experiments compartment D was filled with 5.92 x 10-4 M solution of imipramine hydrochloride and compartment C was filled with
aqueous solution of known concentration of the permeants. In the control experiment, however, no imipramine hydrochloride was used. The initially chosen concentrations of biogenic amines and of cations were comparable to their concentrations in the vicinity of nervous tissue. The condition of no net volume flux (Jv = 0) was imposed on the system by adjusting the pressure head, so that the liquid meniscus in the capillary remained stationary. After a known period of time the concentration of the permeant in another compartment was measured. The amount of permeant gained by compartment D divided by the time and the area of the membrane gave the value of solute flux (Js). The value of solute permeability w was estimated using the definition (9, 10)
(J-iL-)
= to,
[1]
Jv=0
where ~ c is the osmotic pressure difference. The value of ~ v used in the calculations of co was the average of the values of ~ v at the beginning of the experiment (t = 0) and at the end of the experiment. During the permeability measurements, the solution in compartment C was kept well stirred. All measurements were made at constant temperature by placing the transport cell in a thermostat set at 37 _ 0. I°C. Estimations. The amounts of the various permeants transported in compartment D were estimated as follows. Biogenic amines. Imipramine was observed to quench the fluorescence intensity of biogenic amines by inner filter effect; hence the biogenic amines were not estimated by measuring the fluorescence intensity. The absorption maxima for the biogenic amines lies around 275 nm. Hence for the estimation of the amount of biogenic amines transported in compartment D a calibration curve of absorbance versus concentrations of the biogenic amines was constructed using a mixture of constant amount of imipJournal of Colloid and lnterface Science, Vol. 87, No. 1, May 1982
58
SRIVASTAVA, J A K H A R , A N D B H I S E
ramine hydrochloride and varying amounts of the biogenic amines. The same amount of imipramine hydrochloride was added to the solution of compartment D in case of the control and the first set of experiments. The absorbance at 275 nm for this mixture was recorded and from the calibration curve the amount of the transported biogenic amine was computed. In case of second set of the experiments, where imipramine hydrochloride was already in compartment D, no fresh imipramine hydrochloride was added. The mixture of imipramine hydro-
chloride and the biogenic amines were observed to obey Beer's law. Cations. The amounts of sodium, potassium, and calcium ions were determined using an atomic absorption spectrophotometer (Perkin-Elmer model 306). RESULTS AND DISCUSSION
From the hydraulic permeability data at various concentrations of imipramine hydrochloride (Fig. 1), it is obvious that the linear relationship
"1"
4.0
3.0 E O x >
2.0
1.0
0 0
~,.0
I~.0
12.0
16.0
-2 AP X 102--" Nm FIG. 1. The hydraulic permeability data. Curves I to VI are for the case when compartment C was filled with imipramine solutions and compartment D with water. Imipramine concentration for O = 0, A = 0 . 1 4 8 x 10-4M, [] = 0 . 3 7 × 10-4M, • = 0 . 7 4 × 10-4M, • = 1.11 × 10-4M, ® = 1.48 × 10- 4 M , V = 3.70 × 10- 4 M , • = 7.40 × 10- 4 M . Journal of Colloid and Interface Science, Vol. 87, No. 1, May 1982
59
LIQUID-MEMBRANE PHENOMENA
Jv = L e ' A P ,
[2]
where Jv represents the volume flux per unit area of the membrane, AP the applied pressure difference, and Lp, the hydraulic conductivity coefficient, is obeyed in all cases. The values of Lp estimated from the slopes of the curves in Fig. 1 show a progressive decrease as the concentration of imipramine hydrochloride is increased (Table I). The decreasing trend continues up to the CMC, i.e., 1.48 × 10-4 M. When the concentration of imipramine hydrochloride is increased further the value of Le also decreases but this decrease is much less pronounced than the decrease noticed up to the CMC. This trend is in keeping with Kesting's liquid-membrane hypothesis (1-3) according to which as concentration of the surface-active substance is increased the supporting membrane get s progressively covered with the surfactant layer liquid membrane and at the CMC the coverage is complete. The slight decrease in the values of Lp beyond the value of CMC might be due to an increase in density of the liquid membrane as postulated by Kesting et al. (3). Analysis of the flow data (Fig. 1, Table I) in the light of mosaic-membrane model (11-13) further supports the existence of the liquid membrane in series with the supporting membrane. Following the arguments given earlier (8, 14) it can be shown that if the concentration of the surfactant is n times the CMC, n being less than or equal to I, the value of Le would be equal
to {(1 - n)L~ + nL~}, where L~o and L~ respectively represent the values of the hydraulic conductivity coefficient for the bare supporting membrane and the supporting membrane covered with the surfactant layer liquid membrane. Functionally L~, and L~ would be the values of Lp at 0 and the CMC of the surfactant. The values of Lp thus computed for 0.1, 0.25, 0.5, and 0.75 CMC of imipramine are given in Table I. These are in good agreement with the experimentally determined values. The value of co for biogenic amines and cations are recorded in Table II. In order to ensure that the supporting membrane of the transport cell is completely covered with the liquid membrane, the concentration of imipramine hydrochloride chosen for the present experiment was 5.92 × 10-4M which is much higher than its CMC. Since imipramine is surface active in nature, it has both hydrophobic and hydrophilic parts in its structure. The orientation of its molecule will, therefore, be significant when it forms a liquid membrane. The hydrophobic ends of imipramine molecules will be preferentially oriented toward the hydrophobic supporting membrane and their hydrophilic ends will face outward away from it. When imipramine is in compartment C of the transport cell (first set of experiments) the liquid membrane will present a polar surface to the permeants which are present in the same compartment. In the second set of experiments, however, where imipramine is in compartment D of the transport cell and the aqueous solution of the permeant in corn-
TABLE I Values of Le at Various Concentration of Irnipramine Conch. of imipramine (×104 M )
0
0.148 (0.1 C M C )
0.37 (0.25 C M C )
0.74 (0.5 C M C )
1.11 (0.75 C M C )
1.48 (CMC)
Le~ × 10s (m 3 see -~ N -E)
3.369 + 0.05
3.233 _+ 0.09
3.075 ,+ 0.08
2.925 -+ 0.06
2.702 .+ 0.07
2.451 ,+ 0.05
2.444 + 0.07
2.442 -+ 0.08
L~b × l 0 s (m 3 see -I N -I)
--
3.277 .+ 0.05
3.152 + 0.018
2.935 ,+ 0.03
2.718 + 0.041
--
--
--
3.70
7.40
° Experimental values. b Calculated values using mosaic model.
Journal o f Colloid and Interface Science, Vol. 87, No. 1, M a y 1982
60
SRIVASTAVA, JAKHAR, AND BHISE T A B L E II Solute Permeability w of Biogenic Amines and Cations in Presence of 5.92 × 10 -4 M Imipramine
Dopamine Noradrenaline Adrenaline 5-Hydroxytryptamine Sodium (chloride) Potassium (chloride) Calcium (chloride)
Wl (moles N - ' see -1)
~o2 (moles N -~ sec -~)
603 (moles N -t sec -1)
2.657 9.893 4.625 2.272 0.862 4.757 0.566
1.048 4.820 1.768 0.973 0.469 1.383 0.102
4.337 1.210 6.887 9.541 0.712 1.861 0.208
× × × X × X ×
10 -l° 10 -11 10 -1° 10 -1° 10 -~° 10 -1° 10 -t°
X X × × × X ×
10 -l° 10 -11 10 -1° 10 -1° 10 -~° 10 -1° 10 -1°
× × × X × × ×
10 -1° 10 -9 10 -1° 10 -1° 10 -~° 10 -1° 10 -1°
Note. Wl--Control value when no imipramine was used. ¢o2--Imipramine in c o m p a r t m e n t D of the transport cell. o~s--Imipramine in c o m p a r t m e n t C of the transport cell.
partment C, the imipramine liquid membrane would present a hydrophobic surface to the permeant. The orientation of imipramine molecules with respect to approaching permeant would thus be different in the two sets of experiments. The values of oJ recorded in Table II indicate that in the first set of experiments, where the imipramine liquid membrane presents a hydrophilic surface to the permeants, the permeability of biogenic amines is increased. In the second set of experiments, however, where the imipramine liquid membrane presents a hydrophobic surface to the approaching permeant, a marked decrease in the permeability of biogenic amines is observed. Since in vivo imipramine is known to act by reducing the uptake of biogenic amines (6) the present study indicates that the specific orientation of imipramine with hydrophobic ends facing the permeants would also be necessary in the vicinity of nerve terminals. This reduction in the passive transport of biogenic amines and cations (Table II) is also likely to be accompanied by a consequent reduction in their active transport because access of the permeants to the active site located on the nerve membrane is likely to be effectively reduced due to the resistance offered by the liquid membrane interposed in between. Thus although neuronal uptake of biogenic amines is by active process (15) Journal of Colloid and Interface Science, Vol. 87, No. 1, M a y 1982
the formation of liquid membrane by imipramine seems to have a contribution in the mechanism of its action. In certain tissues imipramine is known to increase outflow of noradrenaline (15, 16). This may be because of the specific orientation of imipramine with its hydrophilic ends facing the catecholamines. Presumably even on adrenoceptors similar orientation of imipramine may be necessary. However, more understanding in terms of orientation of imipramine molecule with respect to the relevant biological membrane is necessary. The reduced permeability to cations in both orientations of imipramine can be explained on the basis of hydrophilicity of the ions. This observation may have relevance to the effect of imipramine on nerve conduction. ACKNOWLEDGMENT T h a n k s are due to the D e p a r t m e n t of Science and T e c h n o l o g y , N e w Delhi for financial support. REFERENCES 1. Kesting, R., Vincent, A., and Eberlin, J., O S W R & D Report No. 117, Aug. 1964. 2. Kesting, R. " R e v e r s e O s m o s i s Process U s i n g Surfactant Feed A d d i t i v e s , " O S W , Patent application S A L 830, Nov. 3, 1965. 3. Kesting, R., S u b c a s k y , W. J., and Paton, J. D., J. Colloid Interface Sci. 28, 156 (1968). 4. Felmeister, A., J. Pharm. Sci. 61, 151 (1972).
LIQUID-MEMBRANE PHENOMENA 5. Seeman, P., and Bialy, H. S., Biochem. Pharmacol. 12, 1181 (1963). 6. Shore, P. A.,Ann. Rev. Pharmacol. 12,209 (1972). 7. Palm, D., Grobecker, H., and Bak, I. J., in "New Aspects of Storage and Release Mechanisms of Catecholamines" (H. J. Shumann and G. Kroneberg, Eds.), pp. 188-198. Bayer Symposium II, Springer-Verlag, 1970. 8. Srivastava, R. C., and Jakhar, R. P. S., J. Phys. Chem. 85, 1457 (1981). 9. Katchalsky, A., and Curran, P. F., "Nonequilibrium Thermodynamics in Biophysics." Harvard Univ. Press, Cambridge, Mass., 1967. 10. Katchalsky, A., and Kedem, O., Biophys. J. 2, 53 (1962). 11. Spiegler, K. S., and Kedem, O., Desalination 1, 311 (1966).
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12. Sherwood, T. K., Brain, P. L. T., and Fischer, R. E., Ind. Eng. Chem. Fundam. 6, 2 (1967). 13. Harris, F. L., Humphreys, G. B., and Spiegler, K. S., in "Membrane Separation Processes" (P. Meares, Ed.), Chap. 4. Elsevier, Amsterdam/New York, 1976. 14. Srivastava, R. C., and Yadav, Saroj, J. Colloid Interface Sci. 69, 280 (1979). 15. Iversen, L. L., in "Drugs and Transport Processes" (B. A. Collingham, Ed.), pp. 275-286. Macmillan, New York, 1974. 16. Glowinski, J., in "New Aspects of Storage and Release Mechanisms of Catecholamines" (H. J. Shumann and G. Kroneberg Eds.), pp. 237248. Bayer Symposium II, Springer-Verlag, 1970.
Journal of Colloid and Interface Science, Vol. 87, No. 1, May 1982