EFFECT OF VERAPAMIL ON CA2-ATPASE ACTIVITY IN RAT-BRAIN SYNAPTOSOMES(AND CA(2+) MG (2+))

To elicit the correlation between the adrenergic transmitter release a nd calmodulin (CaM), the effect of verapamil on the free Ca2+ concentr ation was measured with fluorescence analysis and Ca-(2+) Mg-(2+)- ATP ase activity in rat synaptosomes were studied. When stimulated with hi gh-K+ or norepinephrine, the concentration of free Ca2+ in rat synapto some was increased by verapamil 10, 50, and 100 mu mol.L(-1). But the free Ca2+ concentration in the resting synaptosome was reduced by vera pamil. The activity of Ca-(2+) Mg-(2+)-ATPase in synaptosome was remar kably inhibited by verapamil in a dose-dependent manner. These results support our hypothesis that CaM not only acts directly on the vesicle s to enhance the transmitter release, but also acts on the activity of Ca-(2+) Mg-(2+)-ATPase to reduce the free Ca2+ in the cytosol, and in directly inhibited the transmitter release.