K+ and Cl- currents in enterocytes isolated from guinea-pig small intestinal villi

1. The whole-cell configuration of the patch-clamp technique has been used to investigate the conductance properties of villus enterocytes isolated from guinea-pig small intestinal epithelium. 2. With near physiological ionic gradients inward and outward rectification was observed in the hyperpolarizing and depolarizing voltage domains respectively. 3. Replacement of intra- and extracellular K+ with N-methyl-D-glucamine (NMG) eliminated inward rectification but did not alter outward currents. In symmetrical low Cl- solutions outward currents were reduced but inward rectification was not affected. Under these conditions increases in extracellular K+ shifted both the current-voltage relation and the extrapolated reversal potential as expected for a K(+)-selective current. 4. The inwardly rectifying nature of the K+ current observed here remained unaltered after chelation of internal Mg2+ with ATP or EDTA. 5. Extracellular application of 5 mM-Ba2+ or 50 micrograms ml-1 of the venom of the scorpion Leiurus quinquestriatus abolished the inward K+ current, while 5 mM-extracellular tetraethylammonium (TEA) had little effect. 6. The current remaining in the presence of symmetrical Cl- solutions and in the complete absence of K+ rectified outwardly and reversed at 0 mV. The anionic nature of this current was confirmed by replacing Cl- with different anions. SCN- and Br- carried more current than Cl-, while F- and gluconate were less permeant. 7. Anionic currents of villus guinea-pig enterocytes were not stimulated by cyclic AMP and were strongly and reversibly inhibited by the Cl- channel blocker 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB, 10(-5) M). 8. The inwardly rectifying K+ current described here shares some, but not all, characteristics with others previously described. It is postulated that this conductance might function to couple K+ permeability and the Na(+)-K+ pump rate in enterocytes. Absorption of chloride may be mediated by the Cl- channels.