Electrophysiological characteristics of the Necturus proximal duodenal mucosa: effects of ion substitutions.

Abstract

Voltage-sensitive glass micro-electrodes were used to determine the electrical characteristics of Necturus proximal duodenal epithelium. Some comparative experiments with amiloride were performed with gastric antrum. The apical and the basolateral cell membrane potential differences in duodenum averaged -32 mV and -34 mV (cell negative) respectively. The transepithelial potential difference was -2 mV (lumen negative). The EMF across the apical cell membrane was -29 mV and that across the basolateral cell membrane -39 mV. The transepithelial resistance (Rt) of 63 omega cm2 and the paracellular pathway resistance (Rs) of 80 omega cm2 are of magnitudes similar to that previously reported for more distal amphibian small intestine. The apical and basolateral cell membrane resistances, however, were lower than those reported for distal small intestine. Ion permeabilities for Na+, K+ and Cl- across the apical cell membrane were calculated from ion substitution experiments. The permeability sequence across the apical cell membrane was PK:PCl:PNa 3.02:1.31:1.00. Luminal amiloride (10(-4)M) was without significant effect, further indicating a low duodenal membrane conductance for Na+. The low conductances for K+, Na+ and Cl- suggest that the major ion transport modes across the apical duodenal cell membrane are electroneutral in nature. In contrast, amiloride caused a marked increase in the transmembrane potentials in the antrum.