In smooth muscle cells isolated from cerebral blood vessels, histamine activates Cl - channels through an elevation of intracellular Ca 2+ . We investigated whether Cl - currents were also evoked by adenosine triphosphate (ATP) or caffeine in isolated smooth muscle cells from the rabbit basilar artery using the perforated patch-clamp technique. Bath application of 10 μM ATP or 1 mM caffeine (holding potential -60 mV) activated transient inward currents. With prolonged bath application of 10 μM ATP or 1 mM caffeine, oscillatory inward current were sporadically generated. At a holding potential of -40 mV, transient Cl - currents were induced by 10 μM histamine, 10 μM ATP, and 1 mM caffeine, following activation of a K + current. At - 10 or - 20 mV, histamine predominantly activated the K + current. A repetitively activated outward current was induced by membrane depolarization. These results suggest that oscillations in intracellular Ca 2+ induced by histamine, ATP, and caffeine caused Cl - -current activation at the resting membrane potential. This Cl - current may depolarize the membrane and, thus activate voltage-dependent currents, including a Ca 2+ - dependent K + current. Both the Ca 2+ -dependent K + and Cl - currents induced by various stimuli may contribute to the modulation of Ca 2+ influx by reinforcing membrane depolarization.
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