INWARD RECTIFIER K-MUSCLE CELLS FROM RAT RESISTANCE-SIZED CEREBRAL-ARTERIES( CURRENTS IN SMOOTH)

Inward rectifier K+ channels have been implicatedin the control of mem brane potential and external K+induced dilations of small cerebral art eries. In the present study, whole cell K+ currents through the inward rectifier K+ channel were measured in single smooth muscle cells isol ated from the posterior cerebral artery of Wistar-Kyoto rats. The whol e cell K+ current-voltage relationship showed inward rectification. In ward currents were recorded negative to the K+ equilibrium potential, whereas outward currents were small. When extracellular K+ was elevate d, the zero current potential shifted to the new K+ equilibrium potent ial, and the conductance of the inward cu''ent increased. Inward curre nts were reduced by external barium or cesium. Inhibition by barium an d cesium increased with membrane hyperpolarization. The half-inhibitio n constant for barium was 2.2 muM at -60 mV, increasing e-fold for a 2 3-mV depolarization. We provide the first direct measurements of inwar d rectifier K+ currents in single smooth muscle cells and show that ex ternal barium ions are effective blockers of these currents.