[Calcium antagonist properties of valperinol]

Effects of (1R, 3R, 4S, 6R, 7S, 8R, 10R)-3-piperidinomethyl-4-hydroxy - 8 - methoxy - 10 - methyl - 2,9 - dioxatricyclo[4,3,1,0(3,7)]decan (valperinol, GA 30-905) were investigated at the GABA-ergic synapse of crayfish stretch receptor. Valperinol does not affect GABA-induced changes of postsynaptic membrane conductance but reduces postsynaptic inhibition dose-dependently (10(-6)-10(-4) mol/l) and abolishes it completely at 10(-3) mol/l. The lack of direct postsynaptic effects suggests a presynaptic action of valperil. In the frog neuromuscular junction the amplitude of spontaneous and evoked endplate potentials is reduced by valperinol. Voltage-clamp investigations in neurones of Helix pomatia with mainly calcium-carried inward currents reveal a dose-dependent (10(-3)-10(-6) mol/l) inhibition of calcium inward current by valper-lyinol. These findings in preparations of three different species indicate a calcium-antagonistic action of valperinol comparable to verapamil.