Sex differences in membrane potential in the intact perfused rat liver

The electrical potential difference across the plasma membrane was compared in paired livers from male and female rats perfused single-pass with Krebs-bicarbonate buffer. Variability in the membrane potential measured for different cells within the same liver was small (SD = 1.3 mV). The mean membrane potential was 5.1 mV more negative for male livers than for female livers (-30.3 +/- 0.6 vs. -25.2 +/- 1.0 mV, P less than 0.001), and the male liver had a more negative membrane potential than the female liver in all nine pairs studied. No correlation between membrane potential and perfusion rate was seen. Variability among female livers was more than twice as great (range -19.6 to -30.0 mV) as for male livers (range -26.7 to -31.9 mV). These results suggest that hepatic membrane potential may be modulated by sex hormone levels, which are more variable in female animals. Because the hepatic uptake of bile acids such as taurocholate and organic anions such as bilirubin may involve net movement of electrical charge across the plasma membrane, the current results may explain previously reported sex differences in the uptake of these and other electrogenically transported molecules.