External barium and cesium effectively blocked inward rectifier K+ currents in single smooth muscle cells from rat cerebral arteries, with barium showing a half-inhibition constant of 2.2 microM at -60 mV.
This study provides the first direct measurements of inward rectifier K+ currents in single smooth muscle cells from rat cerebral arteries and demonstrates their effective blockade by external barium ions.
Inward rectifier K+ channels have been implicated in the control of membrane potential and external K(+)-induced dilations of small cerebral arteries. In the present study, whole cell K+ currents through the inward rectifier K+ channel were measured in single smooth muscle cells isolated from the posterior cerebral artery of Wistar-Kyoto rats. The whole cell K+ current-voltage relationship showed inward rectification. Inward currents were recorded negative to the K+ equilibrium potential, whereas outward currents were small. When extracellular K+ was elevated, the zero current potential shifted to the new K+ equilibrium potential, and the conductance of the inward current increased. Inward currents were reduced by external barium or cesium. Inhibition by barium and cesium increased with membrane hyperpolarization. The half-inhibition constant for barium was 2.2 microM at -60 mV, increasing e-fold for a 23-mV depolarization. We provide the first direct measurements of inward rectifier K+ currents in single smooth muscle cells and show that external barium ions are effective blockers of these currents.
Quayle et al. (1993) studied this question. External barium or cesium was evaluated on Inward rectifier K+ currents. External barium and cesium effectively blocked inward rectifier K+ currents in single smooth muscle cells from rat cerebral arteries, with barium showing a half-inhibition constant of 2.2 microM at -60 mV.