Simultaneous activation of Ca²⁺-dependent K⁺ and Cl^- currents by various forms of stimulation in the membrane of smooth muscle cells from the rabbit basilar artery

In smooth muscle cells isolated from cerebral blood vessels, histamine activates Cl^-channels through an elevation of intracellular Ca²⁺. 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 Ca²⁺ 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 Ca²⁺- dependent K⁺ current. Both the Ca²⁺-dependent K⁺ and Cl^-currents induced by various stimuli may contribute to the modulation of Ca²⁺ influx by reinforcing membrane depolarization.