title: Effects of changes in mucosal solution Cl- or K+ concentration on cell water volume of Necturus gallbladder epithelium.
abstract: An electrophysiologic technique was used to measure changes in cell water volume in response to isosmotic luminal solution ion replacement. Intracellular Cl- activity (aCl-i) was measured and net flux determined from the changes in volume and activity. Reduction of luminal solution [Cl-] from 98 to 10 mM (Cl- replaced with cyclamate) resulted in a large fall in aCl-i with no significant change in cell water volume. Elevation of luminal solution [K+] from 2.5 to 83.5 mM (K+ replaced Na+) caused a small increase in aCl-i with no change in cell water volume. Exposure of the Necturus gallbladder epithelium to agents that increase intracellular cAMP levels (forskolin and/or theophylline) induces an apical membrane electrodiffusive Cl- permeability accompanied by a fall in aCl-i and cell shrinkage. In stimulated tissues, reduction of luminal solution [Cl-] resulted in a large fall in aCl-i and rapid cell shrinkage, whereas elevation of luminal solution [K+] caused a large, rapid cell swelling with no significant change in aCl-i. The changes in cell water volume of stimulated tissues elicited by lowering luminal solution [Cl-] or by elevating luminal solution [K+] were reduced by 60 and 70%, respectively, by addition of tetraethylammonium (TEA+) to the luminal bathing solution. From these results, we conclude that: (a) In control tissues, the fall in aCl-i upon reducing luminal solution [Cl-], without concomitant cell shrinkage, indicates that the Cl- entry mechanism is electroneutral (Cl-/HCO3-) exchange. (b) Also in control tissues, the small increase in aCl-i upon elevating luminal solution [K+] is consistent with the recent demonstration of a basolateral Cl- conductance. (c) The cell shrinkage elicited by elevation of intracellular cAMP levels results from conductive loss of Cl- (and probably K+). (d) Elevation of cAMP inhibits apical membrane Cl-/HCO-3-exchange activity by 70%. (e) The cell shrinkage in response to the reduction of mucosal solution [Cl-] in stimulated tissues results from net K+ and Cl- efflux via parallel electrodiffusive pathways. (f) A major fraction of the K+ flux is via a TEA(+)-sensitive apical membrane K+ channel.
authors.affiliation: Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77550.
authors.forename: C U
authors.initials: CU
authors.lastname: Cotton
authors.forename: L
authors.initials: L
authors.lastname: Reuss
mesh_terms: D000818:Animals; D001834:Body Water / Q000187:drug effects / Q000378:metabolism; D018118:Chloride Channels; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004563:Electrochemistry; D004848:Epithelium / Q000378:metabolism; D005704:Gallbladder / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism; D009337:Necturus; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013806:Theophylline / Q000494:pharmacology
chemical_list: D018118:Chloride Channels; D008565:Membrane Proteins; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D005576:Colforsin; D019789:Tetraethylammonium; D013806:Theophylline; D000242:Cyclic AMP