The cellular mechanisms underlying the inhibitory effects of phenylephrine on dihydropyridine-sensitive, voltage-dependent Ca 2 + currents recorded from single smooth muscle cells dissociated from the rat anococcygeus muscle were examined. Phenylephrine (0.1-30 μM) produced a concentration-dependent inhibition of the Ca 2 + current; the maximum response occured at a concentration of 10 μM, which inhibited the peak inward current evoked at 0 mV by 57.7 +/- 4% (n = 8). The response to phenylephrine was reduced but not abolished in cells containing 1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid (BAPTA; 10 mM), and it persisted in cells dialysed internally with heparin (5 mg . ml - 1 ). This was despite the fact that both EGTA (5 mM) and heparin were able to block the phenylephrine-induced, Ca 2 + -dependent chloride current recorded in the same cells. The inhibition of the Ca 2 + current produced by phenylephrine was abolished in cells containing guanosine 5'-[β-thio]diphosphate (GDP-β-S) but persisted in cells pre-treated with pertussis toxin. Our results suggest that the inhibition of L-type Ca 2 + current seen following α-adrenoceptor activation occurs by a mechanism independent from the inositol trisphosphate-mediated release of Ca 2 + from intracellular stores.