title: Proximal tubular dopamine production regulates basolateral Na-K-ATPase.
abstract: Regulation of proximal tubular Na-K-adenosine-triphosphatase (ATPase), brush-border membrane Na(+)-H+ antiporter and Na(+)-Pi symporter activity by endogenously produced dopamine was examined in Wistar rats. Na-K-ATPase was measured in basolateral membrane (BLM) fractions permeabilized with alamethicin or sodium dodecyl sulfate (SDS). Carbidopa (5 mg/kg) injected 18 h before removal of kidneys increased maximal activity (Vmax) noncompetitively in cortical BLM but not in other membrane fractions or outer medullary BLM (-2 +/- 4%). Chronic renal denervation did not alter the response. Carbidopa stimulated Na-K-ATPase in cortical BLM from rats eating a normal salt diet with and without 1% saline to drink (+18 +/- 4% and +22 +/- 4%, respectively; P greater than 0.001). Carbidopa did not increase Vmax of BLM Na-K-ATPase from rats eating a low-salt diet (+1.5 +/- 4%); however, when the low-salt diet was supplemented with 1 mM dihydroxyphenylalanine (dopa) to drink for 1 day carbidopa, increased Vmax by 18 +/- 3% (P = 0.018). Carbidopa did not alter the Michaelis constant (Km) for Na or K or inhibitory constant (Ki) for ouabain. Injection of the DA1 antagonist Sch 23390 (2 mg/kg) also increased Na-K-ATPase (18 +/- 4%; P = 0.014). Western blots using a monoclonal alpha-subunit antibody revealed a 22 +/- 8% increase following carbidopa treatment (P = 0.033; n = 19 pairs). Carbidopa had no effect on Na(+)-H+ antiporter activity (22Na uptake) or on Na(+)-32Pi cotransport in brush-border membrane vesicles. These results indicate that dopamine produced in proximal tubules tonically reduces Na-K-ATPase Vmax by decreasing the number of alpha-subunits associated with the BLM.
authors.affiliation: Department of Clinical Biochemistry, University of Toronto, Ontario, Canada.
authors.forename: A D
authors.initials: AD
authors.lastname: Baines
authors.forename: P
authors.initials: P
authors.lastname: Ho
authors.forename: R
authors.initials: R
authors.lastname: Drangova
mesh_terms: D000408:Alamethicin / Q000494:pharmacology; D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D002230:Carbidopa / Q000494:pharmacology; D004039:Diet, Sodium-Restricted; D004298:Dopamine / Q000096:biosynthesis*; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D001552:Benzazepines; D000408:Alamethicin; D012967:Sodium Dodecyl Sulfate; D000254:Sodium-Potassium-Exchanging ATPase; D002230:Carbidopa; D004298:Dopamine