Permeability properties and intracellular ion concentrations of epithelial cells in rat duodenum

Abstract

Effects of the K + concentration in the bathing fluid ([K +] o) on the intracellular K +, Na + and Cl − concentrations ([K +] i, [Na +] i and [Cl −] i) as well as on the electrical potential were studied in rat duodenum. Changes in the mucosal K + concentration ([K +] m), bringing the sum of Na + and K + concentrations to 147.2 mM constant, had little effect on the transmural potential difference (PD t), but did induce marked changes in the mucosal membrane potential ( V m ). As [K +] m increase, ( V m ) was depolarized gradually and obeyed the Nernst equation for a potassium electrode in the range of [K +] m greater than approx. 60 mM. Experiments of ion analyses were carried out on strips of duodenum to determine the effect of changing the external K + concentrations on [K +] i, [Na +] i and [Cl − i]. An increase in [K +] 0 resulted in increases in [K +] i and [Cl -1] i and a decrease in [Na +] i, [K +] i approaching its maximum at [K +] o greater than 70 mM. Such changes in [K +] i and [Na +] i seem to correlate quantitatively with the changes in [K +] o and [Na +] o. The values of the ratio of permeability coefficients, P Na -/P K+ were estimated using the ( V m ) values and intracellular ion concentrations measured in these experiments. The results suggested that there appeared a rather abrupt increase in the P Na+ /P K- ratio from 0 to approx. 0.1, as [K +] m decreased.