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Endothelin 1 and carbachol stimulate, and isoproterenol inhibits Na+-H+ exchage in dog cardiac Purkinje fibres
J Mol
Cell
Cardiol
24 (Supplement
IV)
(1992)
P-4
UNBXPBCTBD BEBAVIOUR OF THE CURRENT, i,, IN SINO-ATRIAL NODE CELLS ON DECREASING BXTERNAL SODIUM CONCENTRATION Won-Kyung Ho, Hilary F.Brown and Denis Noble. University Laboratory of Physiology, Parks Road, Oxford OX1 3PT. The hyperpolarization-activated inward current, i,, has been considered to be a mixed current carried by sodium and potassium ions because its reversal potential (Es) lies between E,, and E, and changing [Na], or [:K], changes Es in the direction expected. We have investigated the effect of reductions in [Na], (Na replaced by N-methylglucamine) on i, in rabbit single sino-atria1 node cells using the whole cell patch clamp technique. When the pipette solution contained K, and [Na], was decreased from 140 r@l to 14 mM, E, shifted from -25.2 + 2.7 mV (n = 3.1) to -54.2 + 3.1 mV (n = 11). The slope conductance obtained from the fully activated current/voltage curve did not, however, show the significant decrease which would be expected from the Goldman-HodgkinKatz (GHK) equation. When K was replaced by Cs in the pipette solution, E, shifted very positive; the slope conductance now decreased on reducing Thus the i, channel shows unusual characteristics which would not Fl,. be expected from the GHK and similar equations.
P-5
The intrinsic buffering power and Na+-H+ exchange in dog cardiac Purkinje fibres. Mei-Lin Wu#, Yung-Zu Tseng*. Department of Physiology, Medical College; and Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan, R.O.C. We used pH-sensitive microelectrodes to measure the intrinsic buffering power (Bi) in dog cardiac Pukinje bicarbonate-free
fibres when Na+-H+ exchange was blocked (zero Na+ or 1SmM amllorlde) in conditions f,HJ?PEs buffered solution). We found that the pi at resting
intracellular pH @Hi) is high (-31 mM), and there was little change’of pi between pHi 7.4 - 6.4 The relationship between pi and pHi can be described by the empirical equation : pi = -4.69 pHi + 64.59. We also found that in the dog Purkinje fibre Na+-H+ exchange (i) is the only pHlregulator during intracellular acidosis in nominal bicarbonate-free solutions, (ii) is an electroneutral antiporter with one external Na+ ion binding site, (iii) has more than 10 internal binding sites for H+ ions (n=lO) and (iv) the Lineweaver-Burk plot shows that raising the external H+ ions exerts a noncompetitive inhibitory effect upon the Na+-H+exchange.
P-6
Endothelin 1 and carbachol stimulate, and isoproterenol inhibits Na+-H+ exchage in dog Cardiac Purkinje fibres. Mei-Lin Wu#, Yung-Zu Tseng*. Department of Physiology, Medical College; and Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan, R.O.C. We used pa-selective microelectrodes to investigate the modulatory effect of endothelin 1 (ENDO; 10mg - IO-* M), carbachol (7.5 X 10e4 M) and isoproterenol (ISO;10-6 M) upon Na+-H* exchange in dog cardiac Parkinje fibres in HEPES buffered solutions. We found that the resting intracellular pH @Hi) is alkalinlzed by 0.09 2 0.01, n=8; and 0.09 c 0.02, n=3, by applying END0 or carbachol separately. There was no change of resting pHi by 10e6M ISO. The pHirecovery after acute intracellular acidosis , by applying 20mM NH,Cl for 10 - 15 min. , was accelerated both by END0 (n=4) and carbachol (n=3), since the curves of net acid efflux vs pHi (activation curves; AC) were both shifted to the right. The AC of ISO, however, was depressed. We suggest that the stimulatory effects upon the antiport of carbachol and END0 are probably due to an increase in protein kinase C ; the inhibitory effect of IS0 is probably due to an elevation of internal CAMP.
S.37
Cell
Cardiol
24 (Supplement
IV)
(1992)
P-4
UNBXPBCTBD BEBAVIOUR OF THE CURRENT, i,, IN SINO-ATRIAL NODE CELLS ON DECREASING BXTERNAL SODIUM CONCENTRATION Won-Kyung Ho, Hilary F.Brown and Denis Noble. University Laboratory of Physiology, Parks Road, Oxford OX1 3PT. The hyperpolarization-activated inward current, i,, has been considered to be a mixed current carried by sodium and potassium ions because its reversal potential (Es) lies between E,, and E, and changing [Na], or [:K], changes Es in the direction expected. We have investigated the effect of reductions in [Na], (Na replaced by N-methylglucamine) on i, in rabbit single sino-atria1 node cells using the whole cell patch clamp technique. When the pipette solution contained K, and [Na], was decreased from 140 r@l to 14 mM, E, shifted from -25.2 + 2.7 mV (n = 3.1) to -54.2 + 3.1 mV (n = 11). The slope conductance obtained from the fully activated current/voltage curve did not, however, show the significant decrease which would be expected from the Goldman-HodgkinKatz (GHK) equation. When K was replaced by Cs in the pipette solution, E, shifted very positive; the slope conductance now decreased on reducing Thus the i, channel shows unusual characteristics which would not Fl,. be expected from the GHK and similar equations.
P-5
The intrinsic buffering power and Na+-H+ exchange in dog cardiac Purkinje fibres. Mei-Lin Wu#, Yung-Zu Tseng*. Department of Physiology, Medical College; and Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan, R.O.C. We used pH-sensitive microelectrodes to measure the intrinsic buffering power (Bi) in dog cardiac Pukinje bicarbonate-free
fibres when Na+-H+ exchange was blocked (zero Na+ or 1SmM amllorlde) in conditions f,HJ?PEs buffered solution). We found that the pi at resting
intracellular pH @Hi) is high (-31 mM), and there was little change’of pi between pHi 7.4 - 6.4 The relationship between pi and pHi can be described by the empirical equation : pi = -4.69 pHi + 64.59. We also found that in the dog Purkinje fibre Na+-H+ exchange (i) is the only pHlregulator during intracellular acidosis in nominal bicarbonate-free solutions, (ii) is an electroneutral antiporter with one external Na+ ion binding site, (iii) has more than 10 internal binding sites for H+ ions (n=lO) and (iv) the Lineweaver-Burk plot shows that raising the external H+ ions exerts a noncompetitive inhibitory effect upon the Na+-H+exchange.
P-6
Endothelin 1 and carbachol stimulate, and isoproterenol inhibits Na+-H+ exchage in dog Cardiac Purkinje fibres. Mei-Lin Wu#, Yung-Zu Tseng*. Department of Physiology, Medical College; and Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan, R.O.C. We used pa-selective microelectrodes to investigate the modulatory effect of endothelin 1 (ENDO; 10mg - IO-* M), carbachol (7.5 X 10e4 M) and isoproterenol (ISO;10-6 M) upon Na+-H* exchange in dog cardiac Parkinje fibres in HEPES buffered solutions. We found that the resting intracellular pH @Hi) is alkalinlzed by 0.09 2 0.01, n=8; and 0.09 c 0.02, n=3, by applying END0 or carbachol separately. There was no change of resting pHi by 10e6M ISO. The pHirecovery after acute intracellular acidosis , by applying 20mM NH,Cl for 10 - 15 min. , was accelerated both by END0 (n=4) and carbachol (n=3), since the curves of net acid efflux vs pHi (activation curves; AC) were both shifted to the right. The AC of ISO, however, was depressed. We suggest that the stimulatory effects upon the antiport of carbachol and END0 are probably due to an increase in protein kinase C ; the inhibitory effect of IS0 is probably due to an elevation of internal CAMP.
S.37