Comparative Studies on the Inhibitory Effects of Calcium Antagonists on Cytosolic Ca²⁺ Levels Increased by High-Potassium or Glutamate in Cultured Rat Cerebellar Granule Cells

Abstract

The inhibitory effects of calcium antagonists on high-potassium or glutamate (Glu) enhanced intracellular calcium ion ([Ca²⁺]_i) levels were studied in cultured cerebellar granule cells. Dosages between 0.5 and 10 μM of flunarizine, nicardipine, SM6586 and SM12565 reduced the rise in [Ca²⁺]_i induced by 50 mM KCl in a dose-dependent manner, although diltiazem, verapamil and nifedipine showed less effects on such [Ca²⁺]_i increases. SM6586, SM12565 and flunarizine at dosages below 10 μM each reduced the magnitude of the [Ca²⁺]_i increase induced by 25 μM Glu, but the other examined calcium antagonists were less effective. These results suggest the dissimilar efficacy of calcium antagonists on the inhibition of [Ca²⁺]_i levels increased by high-potassium and Glu.