Na+/H+ antiporter, V-H+-ATPase and Na+/K+-ATPase immunolocalization in a marine teleost (Myoxocephalus octodecemspinosus)

Abstract

Long-term pH compensation in a marine teleost requires the transepithelial excretion of H+ across the gill epithelium. H+ efflux in the longhorn sculpin (Myoxocephalus octodecemspinosus) is dependent on external sodium ion concentration and is inhibited by known inhibitors of Na+/H+ exchangers. Our model for proton transport suggests acid-excreting cells in the gill with an apical Na+/H+ antiporter and basolateral Na+/K+-ATPase. This model is similar to mammalian kidney and elasmobranch gill epithelium in which a basolateral electrogenic-vacuolar proton pump (V-H+-ATPase) localizes to base-excreting cells. The objective of this study was to detect the presence and location of membrane transporters in marine fish gills using immunohistochemical staining. Our data indicate the presence of an apical and subapical Na+/H+-exchanger 2 (NHE2) in the sculpin gill. NHE2 is present in large, ovoid chloride cells and often colocalizes in the same cells as Na+/K+-ATPase. We also detected V-H+-ATPase immunoreactivity, predominantly in cells at the base of the lamellae, with staining patterns indicative of a basolateral location. The 85 kDa protein detected on immunoblots with anti-NHE2 antibodies was found in both control and acid-infused animals and did not change following a large acute acidosis over 8h.