[Transmembrane ionic currents in smooth muscle cells of rat tail artery]

Whole-cell currents in single smooth muscle cells freshly isolated from the rat tail artery have been studied using patch-clamp recordings techniques. Outward current evoked by depolarizing steps from -70 mV consisted of the initial fast and subsequent sustained components. The former was inhibited by 10 mM nifedipine and Ca(2+)-free solution application whereas the latter decreased by only 16% under these conditions. Caffeine at 4 mM abolished the fast component and only slightly reduced the sustained component. Both component were inhibited by 1 mM TEA+. Adding 10 mM EGTA to the pipette solution abolished the fast outward current. In the presence of 10 mM TEA+ and 4 mM 4-AP an inward current was unmasked. These results suggest that the outward current in these cells is carried mainly via delayed rectifier and Ca(2+)-activated K(+)-channels. 4-AP inhibited the sustained component and had no effect on the initial fast outward current, thus A-current is apparently absent.