INHIBITION BY DIHYDROPYRIDINES OF REGULATORY VOLUME DECREASE AND OSMOLYTE FLUXES IN CULTURED ASTROCYTES IS UNRELATED TO EXTRACELLULAR CALCIUM

The 1,4-dihydropyridines (DHP), nimodipine (NMD) and nitrendipine (NTD) were potent blockers of regulatory volume decrease (RVD) and the volume-associated release of [H-3]taurine and chloride (measured as I-125) in 2-weeks cultured rat cerebellar astrocytes. The IC50 were 30 mu M and 29 mu M for taurine efflux and 26 and 27 mu M for C1 efflux for NMD and NTD, respectively. Inhibition by DHP was independent of extracellular Ca, as the effect was the same in media with 1 mM Ca or without Ca and 0.5 mM EGTA. DHP did not affect the basal (isosmotic) release of [H-3]taurine or I-125 inhibition by DHP (measured only on [H-3]taurine efflux) was the same in 3-4 weeks cultured cerebellar astrocytes, 2-4 weeks cultured cortical astrocytes and 2-weeks cultured cerebellar astrocytes treated with dibutyril cAMP. Diltiazem (50 mu M) and verapamil (100 mu M) failed to inhibit RVD or osmolyte efflux.