CALCIUM CHANNELS AND NIFEDIPINE INHIBITION OF SEROTONIN-INDUCED [H-3] THYMIDINE INCORPORATION IN CULTURED CEREBRAL SMOOTH-MUSCLE CELLS

Cultures of smooth muscle cells were prepared from the basilar artery of adult guinea pigs. Passaged cultures (10-30 passages) that expressed serotonin receptors were studied using [H-3]thymidine incorporation. When tested in quiescent medium, serotonin potently stimulated [H-3]thymidine incorporation (EC50 of 31 nM) by as much as 400% at 24 h. The number of cells was not significantly increased at 24 or 48 h. At concentrations of 10(-8) - 10(-5) M 5-HT, [H-3]thymidine uptake was reduced 40-50% by the dihydropyridine Ca2+ channel blocker, nifedipine (1-mu-M). To demonstrate a possible mechanism for the sensitivity to nifedipine, Ca2+ currents were measured using the whole cell patch clamp technique. The cells expressed dihydropyridine-sensitive L-type Ca2+ channels, but not other subtypes of Ca2+ channels, as indicated by the kinetic and voltage-dependent characteristics of the current and by the stimulatory effect of Bay K 8644. The magnitude of the Ca2+ currents was related exponentially to the membrane surface area, measured as cell capacitance. These data support the association of dihydropyridine-sensitive Ca2+ channels with mitogenesis in vascular smooth muscle, and suggest an alternate mechanism of action for the beneficial effect of dihydropyridines in prophylaxis of cerebral vasospasm.