V-H+-ATPase translocation during blood alkalosis in dogfish gills:: interaction with carbonic anhydrase and involvement in the postfeeding alkaline tide

We investigated the involvement of carbonic anhydrase (CA) in mediating V-H+-ATPase translocation into the basolateral membrane in gills of alkalotic Squolus aconthias. Immutiolabeling revealed that CA is localized in the same cells as V-H+-ATPase. Blood plasma from dogfish injected with acetazolamide [30 mg/kg at time (t) = 0 and 6 h] and infused with NaHCO3 for 12 h (1,000 mu eq(.)kg(-1).h(-1)) had significantly higher plasma HCO3- concentration than fish that were infused with NaHC03 alone (28.72 +/- 0.41 vs. 6.57 +/- 2.47 rnmol/l, n = 3), whereas blood pH was similar in both treatments (8.03 +/- 0.11 vs. 8.04 +/- 0.11 pH units at t = 12 h). CA inhibition impaired V-H+-ATPase translocation into the basolateral membrane, as estimated from immunolabeled gill sections and Western blotting on gill cell membranes (0.24 +/- 0.08 vs. 1.00 +/- 0.28 arbitrary units, n = 3; P < 0.05). We investigated V-H+-ATPase translocation during a postfeeding alkalosis (alkaline tide). Gill samples were taken 24-26 h after dogfish were fed to satiety in a natural-like feeding regime. Immunolabeled gill sections revealed that V-H+-ATPase translocated to the basolateral membrane in the postfed fish. Confirming this result, V-H+-ATPase abundance was twofold higher in gill cell membranes of the postfed fish than in fasted fish (n = 4-5; P < 0.05). These results indicate that 1) intracellular H+ or HCO3- produced by CA (and not blood pH or HCO3-) is likely the stimulus that triggers the V-H+-ATPase translocation into the basolateral membrane in alkalotic fish and 2) V-H+-ATPase translocation is important for enhanced HCO3- secretion during a naturally occurring postfeeding alkalosis.