SWELLING-ACTIVATED CONDUCTANCES FOR CHLORIDE, POTASSIUM AND AMINO-ACIDS IN THE RAT COLON - A WHOLE-CELL STUDY

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.