The localization of Branchial Carbonic Anhydrase in the shark, SQUALUS ACANTHIAS

Differences in gill function, pattern of C02 elimination and ion /acid-base regulation, between elasmobranchs and teleosts are expected to be reflective of differences in the pattern of carbonic anhydase (CA) distribution within the gills of these groups. The distribution of branchial CA was investigated in the spiny dogfish, Squalus acanthias, using immunolocalization techniques, as well as in situ and in vivo measurements of pH disequilibrium states in post-branchial saline and blood, respectively. Biochemical and immunolocalization techniques were used to determine if V-type H+-ATPase was present in the gills of dogfish. In addition, the cellular distribution of H+-ATPase in the gill was determined in fresh and sea water adapted trout, Oncorhynchus mykiss, using immunocytochemical techniques in order to compare its distribution with that of CA in the trout. Branchial CA in the dogfish is distributed throughout the outer epithelial cells and pillar cells. This pattern of CA distribution suggests a role in facilitating diffusion of C02 and in ion / acid-base regulation. The lack of a post-branchial pH disequilibrium in the in situ saline perfused gill preparation suggests that CA is available extracellularly along the blood lumen side of the pillar cell membrane to accelerate the HC03 " dehydration reaction, thus augmenting C02 elimination. The post-branchial pH decrease (acidosis) measured under control conditions in vivo provides equivocal evidence for the in situ finding. In dogfish H -ATPase was localized to a subpopulation of mitochondria-rich (MR) cells in the interlamellar region. There was also significant N-ethymaleimide (NEM) sensitive ATPase activity (0.116 ± 0.026 umol Pj • mg"1 protein • h"1) in crude gill homogenates. The immunolocalized MR cells may function in ion / acid-base regulation. In the trout, H+-ATPase was localized to the apical membrane and subapical vesicles in epithelial pavement and mitochondria-rich cells was confirmed. The apical distribution gradient of the pump is remarkably similar to the distribution found for CA in trout.Land and Food Systems, Faculty ofGraduat