Sodium-potassium-ATPase electrogenicity in cerebral precapillary arterioles

Electrogenicity of the Na+/K+ pump has the capability to generate a large negative membrane potential independently of ion-channel current. The high background membrane resistance of arterioles may make them susceptible to such an effect. Pump current was detected by patch-clamp recording from smooth muscle cells in fragments of arterioles (diameter 24–58 μm) isolated from pial membrane of rabbit cerebral cortex. The current was 20 pA at −60 mV, and the extrapolated zero current potential was −160 mV. Two methods of estimating the effect of pump electrogenicity on resting potential indicated an average contribution of −35 mV. In 20% of the recordings, block of inward rectifier K+ channels by 10–100 μM Ba2+ led to a small depolarization, but hyperpolarization was a more common response. Ba2+ also inhibited depolarization evoked by 20 mM K+. In arterioles within intact pial membrane, Ba2+ failed to evoke constriction but inhibited K+-induced constriction. The data suggest that cerebral arterioles are vulnerable to the hyperpolarizing effect of the Na+/K+pump, excessive effects of which are prevented by depolarizing inward rectifier K+ current