Acid and base secreting cells in leopard shark ( Triakis semifasciata ) gills: mitochondrial richness, ATPase specificity, and vacuolar H+ ATPase (VHA) translocation

Sharks maintain stable blood pH by way of acid and base secreting cells in the gill. Using immunofluorescence, we confirmed the existence of two distinct gill cell types characterized by large abundance of either: vacuolar H+ ATPase (VHA) or Na+/K+ ATPase. Further analysis using antibodies against complex IV, confirmed that both cell types are also mitochondria rich. In VHA‐rich gill cells from dogfish sharks ( Squalus acanthias ) VHA moves from cytoplasmic vesicles to the basolateral membrane in order to rectify blood alkalosis experienced post feeding by pumping protons into alkaline blood. We observed similar VHA translocation occurs in fed leopard sharks. Western blot analyses showed a comparatively greater concentration of VHA in the membrane fraction of fed sharks over starved sharks. Western blots of gill crude homogenate fractions showed steady amounts of VHA, suggesting that the increased VHA content in the membrane of fed sharks result from translocation as opposed to generation of new gill cells with high membrane VHA content. VHA immunofluorescence microscopy of gill sections confirmed that fed sharks have more basolaterally located VHA. Because this phenomenon occurs in both leopard and dogfish sharks, the results suggest that VHA translocation may be a universal mechanism for combating blood alkalosis in marine elasmobranchs. Research was funded by the American Physiological Society UGSR Fellowship to Christian Munévar, the San Diego Fellowship to Jinae N. Roa, and Scripps Startup Funds to Martin Tresguerres.