Effect of H+ and elevated PCO 2on membrane electrical properties of rat cerebral arteries

Some membrane electrical properties of muscle cells from the middle cerebral artery of the rat were recorded with intracellular microelectrodes. The resting membrane potential (E_m) of this preparation was –63 mV. Reduction of extracellular pH to 7.0 in the face of a constantP_CO2of 40 mm Hg had no significant effect onE_m. Similarly the slope of the steady-state voltage/current curves was not different at pH 7.0 compared to control at pH 7.4. In marked contrast, whenP_CO2was elevated to around 60 to 70 mm Hg there was a rapid hyperpolarization and reduction in the slope of the voltage current curve suggesting an increased conductance for one or more ionic species. In addition elevation ofP_CO2increased the slope of theE_m vs. log[K]₀ curve from 46 mV/decade to 59 m V/decade which is in good agreement with a Nernstian potential for a K⁺ selective membrane. These data suggest that while the smooth muscle cells of rat cerebral arteries are relatively insensitive to a small reduction in extracellular pH; reduction of intracellular pH by elevatingP_CO2induces hyperpolarization by increasing K⁺ conductance (g_k). However, it is not clear from these experiments if theP_CO2effects are mediated entirely by changes in pH or if there is a direct membrane action of CO₂.This work is supported by Grant no. HL27862