Calcium channels and nifedipine inhibition of serotonin-induced [³H]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 [³H]thymidine incorporation. When tested in quiescent medium, serotonin potently stimulated [³H]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, [³H]thymidine uptake was reduced 40-50% by the dihydropyridine Ca²⁺ channel blocker, nifedipine (1 μM). 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.