Swelling‐activated conductances for chloride, potassium and amino acids in the rat colon: a whole‐cell study

Abstract

Cell swelling induced by superfusion with a hypotonic medium (152 mosmol l‐1) induced a reversible membrane depolarization of 13.8 +/− 5.3 mV in isolated colonic crypts during whole‐cell recording using nystatin‐permeabilized patches. This depolarization was concomitant with an increase in Cl‐ current as shown by anion substitution. in the absence of Cl‐ ions, the effect of the hypotonic medium was reversed into a hyperpolarization, which was associated with an increase in membrane outward (K+) current. The hyperpolarization was dependent on the presence of Ca2+ ions. It was blocked by TMB‐8 ((N,N‐diethylamino)‐octyl‐3,4,5‐trimethoxy‐benzoate hydrochloride; 10(‐5) mol l‐1), an inhibitor of intracellular Ca2+ release, but not by a Ca2+ channel blocker, verapamil (5 x 10(‐5) mol l‐1). Using butyrate as a stimulus for cell swelling, it was investigated whether swelling induces a conductance for an amino acid, glutamate. in the absence of Cl‐ ions, superfusion with butyrate induced a reversible depolarization when glutamate was present in the intracellular medium, and a reversible hyperpolarization when glutamate was present in the extracellular medium. This response was blocked by the lipoxygenase inhibitor, NDGA (nordihydroguaiaretic acid, 10(‐5) mol l‐1), and was markedly attenuated when glutamate was replaced by the poorly permeable anion, gluconate. Measurements of the membrane current during voltage clamping revealed a modest increase in membrane current carried by glutamate during cell swelling. These results demonstrate that the dominant effect of cell swelling in rat colonic crypts is an increase in Cl‐ conductance, a smaller increase in K+ conductance and a modest increase in conductance of amino acids, such as glutamate. © 1995 The Physiological Society