| Abstract: | Effects of the K+ concentration in the bathing fluid (K+]l) 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 (PDt), but did induce marked changes in the mucosal membrane potential (Vm). As K+]m increased, Vm 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+]o resulted in increases in K+]i and Cl-]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, Pna+/PK+ were estimated using the Vm values and intracellular ion concentrations measured in these experiments. The results suggested that there appeared a rather abrupt increase in the PNa+/PK+ ratio from 0 to approx. 0.1, as K+]m decreased. |
