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Rectification of water flow across the bladder of the toad; effect of vasopressin
Lüe Sciences Vol. 4, pp. 133-140, 1965 . Pergamon Press Ltd. Printed in Great Britain.
R~TIFICATION OF WATER FiAW ACR05S THE
RT .e77r~.R
OF THE TOAD ;EfFECT OF VASOPREacSIN
P, J. Bentley Department of Pharmacology,Univeraity of Bristol
(Received 7 November 1964; in final form 30 November 1964) Introduction The rates of osmotio water transfer across biological membranes may differ men the direction of flow across the membranes is reversed,
This may be observed
by changing the direction but not the magnitude of the o®notic gradient .
Such
asymmetry of membranes has been called rectification of flows and was firot observed in 1845 by Matteucci and Cimeri2 in the skin of frogs and eels .
More
recently these msalts have been confirmed in the frog skin3 and a similar phenomenon has been ahoy to occur in the seed coats of plants, sea
u mhin
eggs 5 , insect cutiale6 and in the bladder of the toad Bufo merinus7in the presence and absence of neurrohypophysial hormone .
The phenomenon is . not
neaessari],y related to the properties of the living membrane : it has been ahoy in synthetic membraneé and has been discussed theoretically in model membranes by Patlak et al . i
The earlier observations on membrane rectification in the
toad bladder in the presence of vasopressin suggested that further investigatlon might be interesting in relation to the phpsiolo~ of sell membranes generally end,in particular, to the mechanism of action of neurok{ypopi}ysial hormones an the toad bladder. Methods Animals Toads (Bufo bufo
were obtained from a local animal dealer .
They wem
kept in terTaria with free access to water and were fed twice a week, Preparation of the isolated bladder This has been described in detail pmvious],y9 .
133
Each lobe of the bladder
194
RECTIFICATION OF WATER FLOW
Vol . 4, No . 2
1s dissected from the pithed toad and tied to a piece of glass tubing,mucoeal aide facing inwazds.
It was filled with 1 ml of the required solution and
placed in a teat-tube containing 35 ml oP frog Ringer solution oP the follovring oompositicn (mY) :
NaCl, 111 ; CaC1 2 , 1.5 ; ~1 3.35; NaI~03, 2.1,. and glucose 5.5 .
This solution was bubbled with air and kept at 20°. ~rimental procedure The direction and magnitude of the osmotic gradient was determined by changing the concentration of the solution on the mucosal surface while keeping the concentration oP the solution at the aerosol side constant .
The solution
on the mucosal aide consisted of various concentrations of choline chloride . The volume used was sae ml . The relative permeability oP each preparation in either direction was measured as follows : initially the preparation wan always f`illcd with the solution that wan k;ypotonic to normal Ringer solution to be tested and allowed to equilibrate for 1 hr .
The bladder was then Pilled with either a i~rpotonic or
hprpertonic solution ( the oxYier oP testing with these soluticna was reversed in alternate preparations) and the time taken for the preparation to lose or gain a atandaxd weight of Fluid measured . When hormone was being used the weight change selected was nearly always 100 mg - without hoxmone it was 30 mg
These volumes were chosen so as to
ensure that the experiment could be completed within 4 hr .
The intervals
between weighings wen adjusted to the speed of water transfer with regular weig~ings at 5 min. intervals when the required weight change was being approached. The time required for the water transfer to take place was calculated from these results.
The accuractiy of the reaulta obtained wen thus within
the 5 min weighing intervals and ns the time nquind to lose the standardized weights wan alwgys in encase of 15 min and mostly a great deal longer, the error was negligible . After this first experimental period the bladder was filled with fresh hypotonic solution and left for 30 min
At the end of this time it was again
Pilled with either hypo- or hypertonic eholine chloride solution and the
Vol. 4, No . 2 procedure repeated .
RECTIFICATION OF WATER FLOW
135
The ratio of the pezmeability of water moving from the
mucosal to aerosol aide and vice versa wsa then calculated from these two results on the same preparation . Hormone Vasopresain (Pitresain,Parke Davia ~ Co . Batch No . LCL267) was used and added as required to the solution on the aerosol side of the bladder.
Results Neurohypophpraial hozmonea increase the pexmeaMlity of the isolated toad bladder to the osmotic flow of water' end this increase meyy take place in either direction across the bladder providing the osmotic gradient is favourable7' ~. Experiments wen performed in t}e presence and abscaoe of vaaopnaain. results are set out in Table 1. TABLE 1 Ratio En~doamosia to Ezosmoais Aeroaa the Isolated Toad Bladder Vasopnasin ab sent
mucoaa -> aerosa / serosa -> muaosa 1. 0
Cat+ ( 1 .5~) Cat+ absent Vaeopresain present 1.
Osmotic gradient constant ; 200mOmm vasopresain ( mu ./ml .) 100 "
2.
3.
"
"
10
1 conc, canotant ; 10 mu ./ml Vasopressin 200 Gradient ( mOmm) » " 100
3.3
± 0,35
2.9 2.1
± 0.19 ± 0.29
2.1 1.5
± 0,29
2,1 ± 0, 39
» » 2.0 50 Calcium concentration increased 5 times ( 7. 5 ml[) ommotic gr~adient 200 mOmm. 2 .6 cono. at aeroaa 7.5 ~ Ca2+ conc .at muaosa 7 .5 mM
Ca2+
D(eana
± 0.11
2.8
± 0.13 ± 0.36
± 0.55 ± 0,75
± S.S . of 8 experiments
The
136
RECTIFICATION OF WATER FLOW
Vol. 4, No. 2
No yaso~reasin present No rectification of water flow across the toad bladder could be demonstrated in the absence of hormone and with a normal quantity of calcium present on the aerosol side .
'Nhen calcium was absent,hovrever, water flowed mote
rapidly from the mucosal to aerosol side than in tha reverse direction, Yasopxessin present 1,
When the osmotic gradient (200 mOsm) was kept constant and the concent-
ration of vasopresain was varied from 1 mu to 100 mq/ml, water moved about trice e.s rapidly from the mucosal to aerosol side of the bladder than in the opposite direction.
Although the quantities of water transferred varied with
the dose of hormone the relative rates of water movement in both directions remained unaltered.
2.
The concentration of vasopressin was kept constant
(10 mu/ml) but the osmotic gradient was varied .
Rectificatia~n of flow was
alwe`ys observed but ao difference in its magnitude could be demonstrated at the different gradients. Calcium concentration increaseä to 7,5 mM Increases in calcium concentration mey lower the permeability of the bladder to water in the presence of vasopressin li, 12 . However, increased calcium concentration on either side of the bladder did not significantly alter rectification of water flow in the presence of vasopressin.
Discussion Rectification of solvent flow across a membrane may occur if then is an active transport of solvent or if there is an active transport of solute such as to influence the osmotic gradient,bring about an electro-osmosis or even affect the structural stability of the system.
Alternatively, as shown
in models, rectification of flow across mqy occur 1 if solvent passes across two non-homogenous membranes arranged in aeries . Rectification of water flow in the presence and absence of vasopressin
was shown previously in the bladder of another species of toad,Bufo marinus 7 . In the absence of hormone water moved abort twice as rapidly from the mucosal
Vol. 4, No . 2
RECTIFICATION OF WATER FLOW
1S7
to eerosal side than in the reverse direction and thin difference doubled in the presence of hormone .
However, sodium was present at the neuoosal Pane of the
bladder in these experimenta,and since this inn is active],y transported from the mucosal to serosal aide 13 , it seemed li.ke]y that it was ooatributing - at least partly - to the observed differences.
In the present ezperiments there
was no sodium at the mucoeal surface and withoat vaaopressin reotiPicatiaai of flow was not observed.
With vaaopressin present, however, water moved twice
as rapidly from the muoosal to seroaal aide then is the reverse direction. These results suggest that is the absence of vaaopresaia, active aodit~ transport me~y contribute to the rectification of solvent flow across the bladder,but that the rectification observed in the presence of hornane is due to other changes in the cells. The bulk of experimental evidence indicates that water trsnsftr across the bladder in the presence of vasopreasin is a passive process and that the hormones alter the properties of the membrane at the mucosal side, though as effect at the aeroeel aide aasnot be ruled out ~.
The present results sre
consistent with such an action at the mucosal surface of the cell altering the relative permeability oP the membrane surfaces, with resulting rectification of flow..
However, the rectification was similar at different ooaaentratiana of
vnaopreasia and this suggests that parallel ahaagea at both mucosal and serosal surfaces are taking pleoe and that same degree of balance in the relative permeabilities of the two avz~saea is maintained. Ia model membranes the rectification of solvent flow may differ with the osmotic gradient aarnae the system.
Increases in osmotic oa~noentratian an the
aeroaal aide of the frog bladder mqy alter its permeability 15 sad it is also possible that the sudden large changes is the osmotic camcentratien as the mucoaal side of the membrane(neceseary to reverse the direction of flow) may influence its properties .
In the present ezperiments it wen found that changes
in the osmotic oanceatrati m and gradient across the bladder did not alter the rectification of water flow and such changes would thus not appear to contribate to the asymmetxyr of flow.
138
RECTIFICATION OF WATER FLOW
Vol . 4, No. 2
17 Calcium is concerned with the stability of many cell membranes 16, Absence of calcium without vasopressin in the system results in increased permeability of the toad bladder to water 11 while increased calcium concentration reduces the enhanced permeability seen in the presence of the hormone 11,12 The latter observatiai suggests tàat displacement of bound calcium may be con cerned with the response of the bladder to the hormone
12 .
The prisent
results ahaw that absence of calcium results in a rectification of water flow across the bladder similar to that obsernd when vasopressi .. is present. ooncentratians of calcium,however,
High
did not alter the degree of rectification
seen in the presence of vasopressin indicating that if its inhibitory effect an the rtsponse is due to an action on the membrane surßacea, this takes place at both surfaces symmetrically and not one of the cell membranes in particular . One aarmot postulate that such a drastic step es removal of calcium mimics the action of vasopressin since calcium is probably needed at many sites in the cells, but the results indicate the possibility that the rectification seen in the presence of vasopresain could result from a selective displacement of bound calcium,
The results also suggest that the distribution of calcium in cell
membranes may contribute to its ability to rectify the flow of water. is rectification of the flow of water across biolo~;.cal membranes likely to be of biological significance?
Thia is unlikely in the toad bladder since
this organ is not normally subjected to hypertonic canditions at the mucosal surface . coons.
~ctification may,however, be an advantage in other biological situFor example,
rectification of water flaw would appear to occur in
fishes which migrate between freshwater and sea-water.
Smith
18
found that
water loss by exoamoais in eels in sea-water amounted to about 4 per cent of the body weight in a dry while urinary losses in freshwater (a measure of endosmoaia) art 6 to 15 per cent of the body in a day
is,
19
.
The osmotic
gradient between the fish and freshwater is only about 300 ~sm compared with 800 m0sm in sea-water. moais than exosmosis.
Thus, in the eel, water moves more readily by endosThe possible importance of calcium is emphasised by the
observation that eels in artificial sea-water without calcium do not survive
Vol. 4, No . 2 for long .
RECTIFICAT10f~T OF WATER FLOW
139
It thus seems likely that an orientatica of biological membranes
in animals restricting water loss relatively more than water gain may well be physiologically important. S~ In the presence of vasopresain and equal but opposite osmotic gradients, water moved twice as rapidlyr from the mucosal to aerosol aide of the urinary bladder of Bufo bufo than in the reverse direction ( = reotificatian of flow) . This difference was not due to active sodium transport.
In the absence of
vasopreasin and sodium trensport,no rectification of water flow was observed. The rectification of water flow observed across the bladder in the presence of vasopreasin was not influenced by the hormone aoaoentration present nor the magnitude of the osmotic gradient.
Rectification of flow across the bladder
was observed when calcium was removed from the Ringer solutiaa eves when vaaopresain was absent.
Aa ezceas of caldum,however, did not alter the degree
rectification of flow seen in the presence of vaeopreain .
The results are
disausaed in relation to the meahaniem of nation of vasopreaain and the possible aignificanae of reotifiaatia:r of water flow through biological membranes. Referenoea 1.
C.S.PATIAS,D.A .GOLS'~IN ead J.F.BDF1~1fAN, J.Theoret . Biol. ~,426 (1963) .
2.
ldATfEOCCI ana c~I (1845) dtea by BSAiRI~P, sYmp .soo.BxP .Bial. 8,94 (i956) .
3.
S.G.HIJF, 'Sleatmlytea in biolo
oal systema' . 8d. A.Y.Shanea.
Omer.Phyaiol . Soc. 205 (l,955) . 4.
S. DSNI~S . Bot. Gaz. ~, 373 (1917) .
5.
B. LIARS and M. MoCDTOI~ON, P}baiol, Rev. 12, 68 (1932) .
6.
J.W .L.BEAMONP, Symp . Soc.Ezp .Biol. 8, 94 (1956) .
7.
P. J. B$NTi~, J. $sdoorin. 22, 95 (1961) .
8.
H. HA1[SURGSEt, Hiochem Z. li, 433 (1908) .
9.
P.J .P~NTIEi, J. Endocdn . iZ, 201 (1958) .
10 .
W.Ii.SARYSR, Endocrlnolo
~, 112 (1960) .
140
RECTIFICATION OF WATER FLOW
11 .
P.J.BSHTLB)f , J. Phdocrin. 18, 327 (1959 ) .
12.
1~J.PETI~ and Ls.E1!lI~MAN, J. Clin.Inveat. ~, 583 (1964) .
~3 .
".LSAF, J.
L,.
B.ILE~YB and A.IF.Al~, J.Gen .Pl~yaiol ., ~2, 905 (1962) .
15 .
P. J.~7.BY, Camap.Hiouhem .Pbyaiol . 12, 233 (1964) .
16 .
L.V.BEILBRDN,
~ end L.B.PAG$, J.Gen . Pi~aiol. 111_, 657 (1958) "
TYie Dynamica of Living Protoplaam .
woademic Preaa: New Yoxic (1956) . 17 .
à.Y.sanr~s, Phaxm.Rev. IA, 165 (1958) .
18.
H.SèQTH,
19 .
Brl[.SHARItA'1T, I. CHBSTBIt JONE,S and D. ~r,T~aw ,
Amer.J .Physiol . Q.~, yA0 (1930) .
Cco~p. Bioahem.Pi~vaiol , il, 9 (1964) . 20 .
Vol. 4, No. 2
B.Y. ~aaua~rr , D. wxr.r .ew and I. CHESTSR JOI~S. Comp . Biochem. Phyaiol. 11, 19 (1964) .
R~TIFICATION OF WATER FiAW ACR05S THE
RT .e77r~.R
OF THE TOAD ;EfFECT OF VASOPREacSIN
P, J. Bentley Department of Pharmacology,Univeraity of Bristol
(Received 7 November 1964; in final form 30 November 1964) Introduction The rates of osmotio water transfer across biological membranes may differ men the direction of flow across the membranes is reversed,
This may be observed
by changing the direction but not the magnitude of the o®notic gradient .
Such
asymmetry of membranes has been called rectification of flows and was firot observed in 1845 by Matteucci and Cimeri2 in the skin of frogs and eels .
More
recently these msalts have been confirmed in the frog skin3 and a similar phenomenon has been ahoy to occur in the seed coats of plants, sea
u mhin
eggs 5 , insect cutiale6 and in the bladder of the toad Bufo merinus7in the presence and absence of neurrohypophysial hormone .
The phenomenon is . not
neaessari],y related to the properties of the living membrane : it has been ahoy in synthetic membraneé and has been discussed theoretically in model membranes by Patlak et al . i
The earlier observations on membrane rectification in the
toad bladder in the presence of vasopressin suggested that further investigatlon might be interesting in relation to the phpsiolo~ of sell membranes generally end,in particular, to the mechanism of action of neurok{ypopi}ysial hormones an the toad bladder. Methods Animals Toads (Bufo bufo
were obtained from a local animal dealer .
They wem
kept in terTaria with free access to water and were fed twice a week, Preparation of the isolated bladder This has been described in detail pmvious],y9 .
133
Each lobe of the bladder
194
RECTIFICATION OF WATER FLOW
Vol . 4, No . 2
1s dissected from the pithed toad and tied to a piece of glass tubing,mucoeal aide facing inwazds.
It was filled with 1 ml of the required solution and
placed in a teat-tube containing 35 ml oP frog Ringer solution oP the follovring oompositicn (mY) :
NaCl, 111 ; CaC1 2 , 1.5 ; ~1 3.35; NaI~03, 2.1,. and glucose 5.5 .
This solution was bubbled with air and kept at 20°. ~rimental procedure The direction and magnitude of the osmotic gradient was determined by changing the concentration of the solution on the mucosal surface while keeping the concentration oP the solution at the aerosol side constant .
The solution
on the mucosal aide consisted of various concentrations of choline chloride . The volume used was sae ml . The relative permeability oP each preparation in either direction was measured as follows : initially the preparation wan always f`illcd with the solution that wan k;ypotonic to normal Ringer solution to be tested and allowed to equilibrate for 1 hr .
The bladder was then Pilled with either a i~rpotonic or
hprpertonic solution ( the oxYier oP testing with these soluticna was reversed in alternate preparations) and the time taken for the preparation to lose or gain a atandaxd weight of Fluid measured . When hormone was being used the weight change selected was nearly always 100 mg - without hoxmone it was 30 mg
These volumes were chosen so as to
ensure that the experiment could be completed within 4 hr .
The intervals
between weighings wen adjusted to the speed of water transfer with regular weig~ings at 5 min. intervals when the required weight change was being approached. The time required for the water transfer to take place was calculated from these results.
The accuractiy of the reaulta obtained wen thus within
the 5 min weighing intervals and ns the time nquind to lose the standardized weights wan alwgys in encase of 15 min and mostly a great deal longer, the error was negligible . After this first experimental period the bladder was filled with fresh hypotonic solution and left for 30 min
At the end of this time it was again
Pilled with either hypo- or hypertonic eholine chloride solution and the
Vol. 4, No . 2 procedure repeated .
RECTIFICATION OF WATER FLOW
135
The ratio of the pezmeability of water moving from the
mucosal to aerosol aide and vice versa wsa then calculated from these two results on the same preparation . Hormone Vasopresain (Pitresain,Parke Davia ~ Co . Batch No . LCL267) was used and added as required to the solution on the aerosol side of the bladder.
Results Neurohypophpraial hozmonea increase the pexmeaMlity of the isolated toad bladder to the osmotic flow of water' end this increase meyy take place in either direction across the bladder providing the osmotic gradient is favourable7' ~. Experiments wen performed in t}e presence and abscaoe of vaaopnaain. results are set out in Table 1. TABLE 1 Ratio En~doamosia to Ezosmoais Aeroaa the Isolated Toad Bladder Vasopnasin ab sent
mucoaa -> aerosa / serosa -> muaosa 1. 0
Cat+ ( 1 .5~) Cat+ absent Vaeopresain present 1.
Osmotic gradient constant ; 200mOmm vasopresain ( mu ./ml .) 100 "
2.
3.
"
"
10
1 conc, canotant ; 10 mu ./ml Vasopressin 200 Gradient ( mOmm) » " 100
3.3
± 0,35
2.9 2.1
± 0.19 ± 0.29
2.1 1.5
± 0,29
2,1 ± 0, 39
» » 2.0 50 Calcium concentration increased 5 times ( 7. 5 ml[) ommotic gr~adient 200 mOmm. 2 .6 cono. at aeroaa 7.5 ~ Ca2+ conc .at muaosa 7 .5 mM
Ca2+
D(eana
± 0.11
2.8
± 0.13 ± 0.36
± 0.55 ± 0,75
± S.S . of 8 experiments
The
136
RECTIFICATION OF WATER FLOW
Vol. 4, No. 2
No yaso~reasin present No rectification of water flow across the toad bladder could be demonstrated in the absence of hormone and with a normal quantity of calcium present on the aerosol side .
'Nhen calcium was absent,hovrever, water flowed mote
rapidly from the mucosal to aerosol side than in tha reverse direction, Yasopxessin present 1,
When the osmotic gradient (200 mOsm) was kept constant and the concent-
ration of vasopresain was varied from 1 mu to 100 mq/ml, water moved about trice e.s rapidly from the mucosal to aerosol side of the bladder than in the opposite direction.
Although the quantities of water transferred varied with
the dose of hormone the relative rates of water movement in both directions remained unaltered.
2.
The concentration of vasopressin was kept constant
(10 mu/ml) but the osmotic gradient was varied .
Rectificatia~n of flow was
alwe`ys observed but ao difference in its magnitude could be demonstrated at the different gradients. Calcium concentration increaseä to 7,5 mM Increases in calcium concentration mey lower the permeability of the bladder to water in the presence of vasopressin li, 12 . However, increased calcium concentration on either side of the bladder did not significantly alter rectification of water flow in the presence of vasopressin.
Discussion Rectification of solvent flow across a membrane may occur if then is an active transport of solvent or if there is an active transport of solute such as to influence the osmotic gradient,bring about an electro-osmosis or even affect the structural stability of the system.
Alternatively, as shown
in models, rectification of flow across mqy occur 1 if solvent passes across two non-homogenous membranes arranged in aeries . Rectification of water flow in the presence and absence of vasopressin
was shown previously in the bladder of another species of toad,Bufo marinus 7 . In the absence of hormone water moved abort twice as rapidly from the mucosal
Vol. 4, No . 2
RECTIFICATION OF WATER FLOW
1S7
to eerosal side than in the reverse direction and thin difference doubled in the presence of hormone .
However, sodium was present at the neuoosal Pane of the
bladder in these experimenta,and since this inn is active],y transported from the mucosal to serosal aide 13 , it seemed li.ke]y that it was ooatributing - at least partly - to the observed differences.
In the present ezperiments there
was no sodium at the mucoeal surface and withoat vaaopressin reotiPicatiaai of flow was not observed.
With vaaopressin present, however, water moved twice
as rapidly from the muoosal to seroaal aide then is the reverse direction. These results suggest that is the absence of vaaopresaia, active aodit~ transport me~y contribute to the rectification of solvent flow across the bladder,but that the rectification observed in the presence of hornane is due to other changes in the cells. The bulk of experimental evidence indicates that water trsnsftr across the bladder in the presence of vasopreasin is a passive process and that the hormones alter the properties of the membrane at the mucosal side, though as effect at the aeroeel aide aasnot be ruled out ~.
The present results sre
consistent with such an action at the mucosal surface of the cell altering the relative permeability oP the membrane surfaces, with resulting rectification of flow..
However, the rectification was similar at different ooaaentratiana of
vnaopreasia and this suggests that parallel ahaagea at both mucosal and serosal surfaces are taking pleoe and that same degree of balance in the relative permeabilities of the two avz~saea is maintained. Ia model membranes the rectification of solvent flow may differ with the osmotic gradient aarnae the system.
Increases in osmotic oa~noentratian an the
aeroaal aide of the frog bladder mqy alter its permeability 15 sad it is also possible that the sudden large changes is the osmotic camcentratien as the mucoaal side of the membrane(neceseary to reverse the direction of flow) may influence its properties .
In the present ezperiments it wen found that changes
in the osmotic oanceatrati m and gradient across the bladder did not alter the rectification of water flow and such changes would thus not appear to contribate to the asymmetxyr of flow.
138
RECTIFICATION OF WATER FLOW
Vol . 4, No. 2
17 Calcium is concerned with the stability of many cell membranes 16, Absence of calcium without vasopressin in the system results in increased permeability of the toad bladder to water 11 while increased calcium concentration reduces the enhanced permeability seen in the presence of the hormone 11,12 The latter observatiai suggests tàat displacement of bound calcium may be con cerned with the response of the bladder to the hormone
12 .
The prisent
results ahaw that absence of calcium results in a rectification of water flow across the bladder similar to that obsernd when vasopressi .. is present. ooncentratians of calcium,however,
High
did not alter the degree of rectification
seen in the presence of vasopressin indicating that if its inhibitory effect an the rtsponse is due to an action on the membrane surßacea, this takes place at both surfaces symmetrically and not one of the cell membranes in particular . One aarmot postulate that such a drastic step es removal of calcium mimics the action of vasopressin since calcium is probably needed at many sites in the cells, but the results indicate the possibility that the rectification seen in the presence of vasopresain could result from a selective displacement of bound calcium,
The results also suggest that the distribution of calcium in cell
membranes may contribute to its ability to rectify the flow of water. is rectification of the flow of water across biolo~;.cal membranes likely to be of biological significance?
Thia is unlikely in the toad bladder since
this organ is not normally subjected to hypertonic canditions at the mucosal surface . coons.
~ctification may,however, be an advantage in other biological situFor example,
rectification of water flaw would appear to occur in
fishes which migrate between freshwater and sea-water.
Smith
18
found that
water loss by exoamoais in eels in sea-water amounted to about 4 per cent of the body weight in a dry while urinary losses in freshwater (a measure of endosmoaia) art 6 to 15 per cent of the body in a day
is,
19
.
The osmotic
gradient between the fish and freshwater is only about 300 ~sm compared with 800 m0sm in sea-water. moais than exosmosis.
Thus, in the eel, water moves more readily by endosThe possible importance of calcium is emphasised by the
observation that eels in artificial sea-water without calcium do not survive
Vol. 4, No . 2 for long .
RECTIFICAT10f~T OF WATER FLOW
139
It thus seems likely that an orientatica of biological membranes
in animals restricting water loss relatively more than water gain may well be physiologically important. S~ In the presence of vasopresain and equal but opposite osmotic gradients, water moved twice as rapidlyr from the mucosal to aerosol aide of the urinary bladder of Bufo bufo than in the reverse direction ( = reotificatian of flow) . This difference was not due to active sodium transport.
In the absence of
vasopreasin and sodium trensport,no rectification of water flow was observed. The rectification of water flow observed across the bladder in the presence of vasopreasin was not influenced by the hormone aoaoentration present nor the magnitude of the osmotic gradient.
Rectification of flow across the bladder
was observed when calcium was removed from the Ringer solutiaa eves when vaaopresain was absent.
Aa ezceas of caldum,however, did not alter the degree
rectification of flow seen in the presence of vaeopreain .
The results are
disausaed in relation to the meahaniem of nation of vasopreaain and the possible aignificanae of reotifiaatia:r of water flow through biological membranes. Referenoea 1.
C.S.PATIAS,D.A .GOLS'~IN ead J.F.BDF1~1fAN, J.Theoret . Biol. ~,426 (1963) .
2.
ldATfEOCCI ana c~I (1845) dtea by BSAiRI~P, sYmp .soo.BxP .Bial. 8,94 (i956) .
3.
S.G.HIJF, 'Sleatmlytea in biolo
oal systema' . 8d. A.Y.Shanea.
Omer.Phyaiol . Soc. 205 (l,955) . 4.
S. DSNI~S . Bot. Gaz. ~, 373 (1917) .
5.
B. LIARS and M. MoCDTOI~ON, P}baiol, Rev. 12, 68 (1932) .
6.
J.W .L.BEAMONP, Symp . Soc.Ezp .Biol. 8, 94 (1956) .
7.
P. J. B$NTi~, J. $sdoorin. 22, 95 (1961) .
8.
H. HA1[SURGSEt, Hiochem Z. li, 433 (1908) .
9.
P.J .P~NTIEi, J. Endocdn . iZ, 201 (1958) .
10 .
W.Ii.SARYSR, Endocrlnolo
~, 112 (1960) .
140
RECTIFICATION OF WATER FLOW
11 .
P.J.BSHTLB)f , J. Phdocrin. 18, 327 (1959 ) .
12.
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