Effects of potassium ions and sodium ions on membrane potential of epithelial cells in rat duodenum

Abstract

1. 1. Mucosal and serosal membrane potentials ( V m and V s) of epithelial cells in rat duodenum were recorded together with the transmural potential differences ( PD t). 2. 2. The value of V m in rat duodenum at 37°C was about −53 mV, being cosiderably greater than the values reported hitherto for the small intestine of various species. 3. 3. When Cl - in the mucosal medium was partially replaced with So 4 2- at fixed mucosal Na + and K + concentrations ([Na +] m and [K +] m), the membrane potential was affected in the steady state several minutes after replcement, whereas marked changes in the potential were observed with varying [K +] m or [Na +] m. 4. 4. As the mucosal K + concentration increased at constant [Na +] m, V m was gradually decreased (deploration), together with the increase in PD t. such a change in V m caused by varying [K +] m obeys Nernst's equation in the range of [K +] m higher than about 60 mm. 5. 5. At constant [K +] m, an increase in [Na +] m also caused the decrese of V m for the lower [k +] m region, whereas V m was not affected by such changes in [Na +] m in the range of [K +] m higher than approx. 60 mm. 6. 6. The values of P Na/ P k were obtained from the modified Goldman equation under an appropiate assumption. The ratio of the permeability coefficients markedly increases from zero to approx. 0.07 with a decrease in [K +] m.