Effect of verapamil on 45Ca uptake by synaptosomes.

Abstract

The effect of verapamil on K-stimulated 45Ca uptake (the difference between uptake in 60 mM-Ko medium and 5 mM-Ko medium) was studied using a synaptosomal fraction from rat brain. Verapamil inhibited K-stimulated 45Ca uptake, but not 45Ca uptake in 5 mM-Ko media (1 mM- and 0.1 mM-Cao media). The concentrations of verapamil inducing 50% inhibition of K-stimulated 45Ca uptake (ID50) in 1 mM- and 0.1 mM-Cao media were not significantly different, being .apprx. 10-4 M and 2 .times. 10-4 M, respectively. Like verapamil, Mn2+ inhibited only K-stimulated 45Ca uptake, but its ID50 values in 1 mM- and 0.1 mM-Cao media were .apprx. 1.7 mM and 0.2 mM, respectively. Verapamil and Mn3+ specifically inhibit K-stimulated 45Ca uptake, but that the modalities of their inhibitory effects on K-stimulated 45Ca uptake are different.