[Spontaneous transient outward currents in smooth muscle cells of the rat tail artery]

Spontaneous transient outward currents (STOCs) were studied in the rat tail artery smooth muscle cells using standard patch-clamp recording techniques in the whole-cell configuration. STOCs evoked by membrane depolarization from -30 to 20 mV varied in size from 50 to 1000 pA, their amplitude increased with membrane depolarization. These currents were inhibited by 1 mM TEA+. Both the frequency and the transferred charge (Q) were decreased in the absence of the extracellular Ca2+ or in the presence of the selective blocker of voltage-gated L-type Ca2+ channels nifedipine. Application of caffeine at 1 mM increased both Q and the frequency of STOCs generation. These results indicate that STOCs are carried by large conductance Ca(2+)-dependent K+ channels and Ca2+ influx plays an important role in their activation.