title: Possible role of basolateral cell membrane in proximal renal tubule osmoregulation.
abstract: The cellular response to hypotonic stimulation was studied with videometric methods in 266 proximal renal tubules dissected from Carassius auratus (goldfish). In hypotonic solutions (low NaCl), cells underwent rapid swelling followed by gradual shrinking toward isotonic volume (volume-regulatory decrease phase, VRD). Hypothermia (8 degrees C), increased extracellular potassium (15, 25, and 40 mM), quinine (0.1 mM), barium (0.5 mM), 4,4'-diisothio-cyanostilbene-2,2'-disulfonic acid (DIDS; 0.02 mM), acetazolamide (0.1 mM), decrements in extracellular bicarbonate, and increases in extracellular chloride impaired VRD. Ouabain (1.0 mM), furosemide (0.1 mM), and the chloride channel blocker 5-nitro-2-(3-phenylpropylalanine) benzoate (NPPB; 0.001 mM) had no effect. While VRD occurred in the absence of extracellular calcium influx, addition of the calcium ionophore A23187 (0.01 mM) in the presence of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA; 2.0 mM) impaired this process both in acidic and alkaline media. Trifluoroperazine (0.01 mM) reversibly inhibited VRD. The effect of this calmodulin inhibitor could not be overridden with the cationic ionophore gramicidin (0.5 microM). The data suggest that Carassius proximal renal tubular cells volume regulate in hypotonic solutions by the loss of KCl and osmotically obligated water. We postulate that the main efflux of potassium is through a calcium-gated potassium channel with its counter ion extruded through a calmodulin-regulated Cl(-)-HCO3- exchanger.
authors.affiliation: Laboratory Service, Veterans Administration Medical Center, Salt Lake City, Utah 84148.
authors.forename: D
authors.initials: D
authors.lastname: Terreros
authors.forename: H
authors.initials: H
authors.lastname: Kanli
authors.forename: J
authors.initials: J
authors.lastname: Coombs
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002462:Cell Membrane / Q000502:physiology; D002712:Chlorides / Q000378:metabolism; D005399:Fishes; D005665:Furosemide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D010042:Ouabain / Q000494:pharmacology; D014268:Trifluoperazine / Q000494:pharmacology; D014882:Water-Electrolyte Balance / Q000187:drug effects
chemical_list: D002147:Calmodulin; D002712:Chlorides; D014268:Trifluoperazine; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D010042:Ouabain; D005665:Furosemide; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium