NONSELECTIVE CATION CHANNELS IN CEREBROVASCULAR SMOOTH-MUSCLE CELLS OF ADULT-RATS

Inside-out patch clamp recordings have revealed the presence of a nove l, large conductance channel of the non-selective, cation permeable ty pe in smooth muscle cells dispersed from the cerebral arteries of adul t rats. In physiologically appropriate ionic gradients, current flow i n these channels reversed polarity at a membrane potential of about -4 2 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 P-N a/P-K = 0.15, while Cl- was effectively impermeant. Calcium ions were weakly permeant (P-Ca/P-K = 0.03, P-Ca/P-Na = 0.20). Channel open prob ability increased with membrane depolarization and was weakly dependen t on the concentration of free intracellular Ca2+. This channel would contribute outward membrane current at potentials more positive than a bout -42 mV. In concert with outward potassium currents, it may serve to limit membrane depolarization during action potential activity in c erebrovascular smooth muscle cells.