title: 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.
authors.affiliation: Institut für Veterinär-Physiologie, Universität Zürich, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Diener
authors.forename: E
authors.initials: E
authors.lastname: Scharrer
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D002087:Butyrates / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D048429:Cell Size; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D003106:Colon / Q000166:cytology / Q000378:metabolism*; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism; D007038:Hypotonic Solutions; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism*; D009637:Masoprocol / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D051381:Rats
chemical_list: D000596:Amino Acids; D002087:Butyrates; D002121:Calcium Channel Blockers; D018118:Chloride Channels; D002712:Chlorides; D007038:Hypotonic Solutions; D018698:Glutamic Acid; D009637:Masoprocol; D000255:Adenosine Triphosphate; D011188:Potassium; D002118:Calcium