The Effect of Ouabain on the Release of [14C]Acetylcholine and Other Substances from Synaptosomes |
| |
Authors: | S. Vyas R. M. Marchbanks |
| |
Affiliation: | Department of Biochemistry, Institute of Psychiatry, De Crespigny Park, London, U.K. |
| |
Abstract: | Abstract: The effect of ouabain and dihydroouabain on Na+-K+ ATPase, 86Rb uptake and the release of [14C]ACh (acetylcholine) from synaptosomal preparations of guinea pigs was compared. At low concentrations of glycoside (<50 μm ) there was a good correlation between the potency of ouabain and of dihydroouabain in inhibiting Na+-K+ ATPase and in causing the release of [l4C]ACh in a nondepolarising medium. Ouabain (200 μM) increased the release of [14C]ACh evoked by 25 mm -KCl, but not that evoked by 100μm -veratrine. The enhancement of release was independent of the presence of calcium. It was observed that in addition to [14C]ACh release, choline efflux was also stimulated by ouabain, independently of the presence of Ca2+. Experiments with hemicholinium-3 showed that the ouabain-induced increase in choline efflux was not due to an inhibition of reuptake. The effect of ouabain on intrasynaptosomal K+ concentration was measured in order to investigate the degree of depolarisation it caused. The decrease in K+ was found to be similar in magnitude and time course to that caused by veratrine. It was shown that ouabain-induced depolarisation caused an increased efflux of another positive ion (dibenzyldimethylammonium chloride) and retention of a negatively charged ion (chloride), as would be expected from the operation of the electrochemical potential gradient changing as a result of depolarisation. It is suggested that ouabain acts to stimulate ACh release from synaptosomes as follows: following blockage of the Na+-K+ ATPase there is rapid depolarisation which, if Ca2+ is present, provokes the normal Ca2+-dependent transmitter release process to occur. In addition, depolarisation accelerates the leakage of positive ions down their electrochemical potential gradient, but causes a retention of negative ions. Such an action does not depend on the presence of Ca2+, nor is it specific to transmitters. |
| |
Keywords: | Ouabain Neurotransmitters Synaptosomes Release Electrolytes. |
|
|