Effect of temperature on transmembrane potential of mouse liver cells

Mouse liver transmembrane potential (Vm), 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 (EK and ENa) were -88 and 48 mV. Vm also varied as a linear function of temperature. In the range of 37-27 degrees 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 EK accounted for only a small portion of the total decrease in Vm resulting due to cooling from 37 to 25 degrees C. In contrast, slopes of the linear portion of Vm versus log10 external K+ activity were -24 and -14 mV/10-fold change in external K+ activity at 37 and 25 degrees C, respectively. This is consistent with an increase of membrane Na+- to -K+ permeability ratio (PNa/PK) with cooling. Ba2+ and quinine, which block membrane K+ channels, reversibly inhibited increases in hepatocyte Vm resulting due to heating from 37 to 40 degrees C. This suggests that membrane PK varies directly with temperature. We postulate that effects of temperature on liver Vm 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.