Simultaneous Activation of Ca^<2+>-Dependent K^+ and Cl^- Currents by Various Forms of Stimulation in the Membrane of Smooth Muscle Cells from the Rabbit Basilar Artery

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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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