Non-selective cation channels in cerebrovascular smooth muscle cells of adult rats

AbstractInside-out patch clamp recordings have revealed the presence of a novel, large conductance channel of the non-selective, cation permeable type in smooth muscle cells dispersed from the cerebral arteries of adult rats. In physiologically appropriate ionic gradients, current flow in these channels reversed polarity at a membrane potential of about −42 mV. Single channel conductance in symmetrical 140 mM K+ salines was 211 pS. The channel was permeable to both K+ and Na+ with a ratio PNa/PK = 0.15, while Cl− was effectively impetmeant. Calcium ions were weakly permeant (PCa/PK = 0.03, PCa/PNa = 0.20). Channel open probability increased with membrane depolarization and was weakly dependent on the concentration of free intracellular Ca2+. This channel would contribute outward membrane current at potentials more positive than about −42 mV. In concert with outward potassium currents, it may serve to limit membrane depolarization during action potential activity in cerebrovascular smooth muscle cells