title: Potassium depletion increases proton pump (H(+)-ATPase) activity in intercalated cells of cortical collecting duct.
abstract: Intercalated cells (ICs) from kidney collecting ducts contain proton-transporting ATPases (H(+)-ATPases) whose plasma membrane expression is regulated under a variety of conditions. It has been shown that net proton secretion occurs in the distal nephron from chronically K(+)-depleted rats and that upregulation of tubular H(+)- ATPase is involved in this process. However, regulation of this protein at the level of individual cells has not so far been examined. In the present study, H(+)-ATPase activity was determined in individually identified ICs from control and chronically K(+)-depleted rats (9-14 days on a low-K(+) diet) by monitoring K(+)- and Na(+)-independent H(+) extrusion rates after an acute acid load. Split-open rat cortical collecting tubules were loaded with the intracellular pH (pH(i)) indicator 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, and pH(i) was determined by using ratiometric fluorescence imaging. The rate of pH(i) recovery in ICs in response to an acute acid load, a measure of plasma membrane H(+)-ATPase activity, was increased after K(+) depletion to almost three times that of controls. Furthermore, the lag time before the start of pH(i) recovery after the cells were maximally acidified fell from 93.5 +/- 13.7 s in controls to 24.5 +/- 2.1 s in K(+)-depleted rats. In all ICs tested, Na(+)- and K(+)-independent pH(i) recovery was abolished in the presence of bafilomycin (100 nM), an inhibitor of the H(+)-ATPase. Analysis of the cell-to-cell variability in the rate of pH(i) recovery reveals a change in the distribution of membrane-bound proton pumps in the IC population of cortical collecting duct from K(+)-depleted rats. Immunocytochemical analysis of collecting ducts from control and K(+)-depleted rats showed that K(+)-depletion increased the number of ICs with tight apical H(+)ATPase staining and decreased the number of cells with diffuse or basolateral H(+)-ATPase staining. Taken together, these data indicate that chronic K(+) depletion induces a marked increase in plasma membrane H(+)ATPase activity in individual ICs.
authors.affiliation: Department of Physiology and Biophysics, Joan and Sanford I. Weill Medical College of Cornell University, New York, New York 10021, USA. rbsilve@mail.med.cornell.edu
authors.forename: R B
authors.initials: RB
authors.lastname: Silver
authors.forename: S
authors.initials: S
authors.lastname: Breton
authors.forename: D
authors.initials: D
authors.lastname: Brown
mesh_terms: D000136:Acid-Base Equilibrium / Q000187:drug effects; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D004573:Electrolytes / Q000097:blood; D005260:Female; D005452:Fluoresceins / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry; D007685:Kidney Tubules, Collecting / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D018942:Macrolides; D008297:Male; D017419:Potassium, Dietary / Q000378:metabolism* / Q000494:pharmacology; D054328:Proton Pump Inhibitors; D017494:Proton Pumps / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012982:Sodium, Dietary / Q000378:metabolism / Q000494:pharmacology; D014882:Water-Electrolyte Balance / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents; D004573:Electrolytes; D005452:Fluoresceins; D005456:Fluorescent Dyes; D018942:Macrolides; D017419:Potassium, Dietary; D054328:Proton Pump Inhibitors; D017494:Proton Pumps; D012982:Sodium, Dietary; D000643:Ammonium Chloride; C057620:bafilomycin A; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein