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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

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

¹Department of Biological Sciences, University of Alberta, Edmonton, Alberta; ²Bamfield Marine Sciences Centre, Bamfield, British Columbia; and ³Department of Biology, McMaster University, Hamilton, Ontario, Canada

Submitted 17 November 2006 ; accepted in final form 2 January 2007

We investigated the involvement of carbonic anhydrase (CA) in mediating V-H⁺-ATPase translocation into the basolateral membrane in gills of alkalotic Squalus acanthias. Immunolabeling 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 µeq·kg^–1·h^–1) had significantly higher plasma HCO₃^– concentration than fish that were infused with NaHCO₃ alone (28.72 ± 0.41 vs. 6.57 ± 2.47 mmol/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.

Squalus acanthias; bicarbonate secretion; proton reabsorption; acid-base regulation; acetazolamide; ion transport; feeding

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