Effect of Temperature on Transmembrane Potential of Mouse Liver Cells

Mouse liver transmembrane potential (V(m)), measured under steady-state conditions with conventional microelectrodes, was -40 ± 0.6 mV, and intracellular Na+ and K+ activities, measured with liquid ion-exchanger ion-sensitive microelectrodes, were 17 ± 2 and 104 ± 4 mM, respectively. The corresponding K+ and Na+ equilibrium potentials (E(K) and E(Na)) were -88 and 48 mV. V(m) also varied as a linear function of temperature. In the range of 37-27°C, the temperature coefficient (Q10) of 1.61 was greater than the Q10 of 1.033 predicted for a direct proportion of absolute temperature. A decrease in hepatocyte E(K) accounted for only a small portion of the total decrease in V(m) resulting due to cooling from 37 to 25°C. In contrast, slopes of the linear portion of V(m) versus log10 external K+ activity were -24 and -14 mV/10-fold change in external K+ activity at 37 and 25°C, respectively. This is consistent with an increase of membrane Na+ - to -K+ permeability ratio (P(Na)/P(K)) with cooling. Ba2+ and quinine, which block membrane K+ channels, reversibly inhibited increases in hepatocyte V(m) resulting due to heating from 37 to 40°C. This suggests that membrane P(K) varies directly with temperature. We postulate that effects of temperature on liver V(m) result from temperature effects on membrane K+ channel conductance and on the Na+-K+ pump. The results also are consistent with temperature effects on kinetic parameters for opening and closing of membrane K+ channels