HCO3−-Dependent ATPase activity in the gills of rainbow trout Salmo gairdneri

Localization of Na/K-ATPase sites in the secretory and reabsorptive epithelia of perfused eccrine sweat glands: A question to the role of the enzyme in secretion

“…On the other hand, there is some evidence for a HCO3 stimulated ATPase. Conceivably this enzyme might be involved in transporting Na § in either a H § exchange or in coupled HCO3 transport [20,39]. In any case, it is not possible at this point to favor any of the alternatives, but in light of current findings, the question of their existence may be raised more seriously.…”

Effects of Age and Coion (K+and Na+) on the Toxicity of Thiocyanate to Rainbow Trout (Oncorhynchus mykiss) during Pulse or Continuous Exposure

“…SCN − is known to inhibit the uptake of negatively charged ions such as HCO 3 − , but not positively charged ones (Heming et al, 1985). Although effects on K + flux have not been reported for KSCN, studies on NaSCN indicate that the SCN − ion does not alter the flux of Na + across gill membranes in goldfish (Carassius auratus) (De Renzis, 1975;Epstein et al, 1973) or rainbow trout (Kerstetter and Kirshner, 1974). If SCN − does not impact K + or Na + fluxes directly, it is possible that the altered ratios of K + to Na + at the gill surface during KSCN versus NaSCN exposure alter the relative availability of the two ions, changing the electrical potential of the cells and hence toxicity; further research is required for a definitive answer.…”

Active chloride transport in the in vitro opercular skin of a teleost (Fundulus heteroclitus), a gill‐like epithelium rich in chloride cells

“…Assuming that the intracellular chloride cell HC03-concentration is in equilibrium with the extracellular HCO3-concentration, increasing the latter would lead to an increase in the intracellular HCO3-and an increased activity of the HCO3--activated ATPase. If this enzyme supplied the energy for the active Cl-transport, a stimulation of its activity by HCO3-would explain the influence of this anion on Cl-secretion across the opercular epithelium. The drawbacks to this hypothesis are that this enzyme has yet to be identified in this epithelium, no definite link between this HC03--activated ATPase and active Cl-transport has been established, this enzyme is not activated by Cl-, and it appears to be located primarily in the mitochondrial fraction of gill homogenates (Kerstetter & Kirschner, 1974;Solomon et al 1975) rather than in the membrane fraction. The chloride cells are rich in mitochondria and the opercular epithelium of F. heteroclitws is predominantly chloride cells, which suggests that this epithelium may be rich in this HC037-activated ATPase.…”

“…Perhaps other carbonic anhydrase inhibitors may produce different results. The HCO3--activated, SCN--inhibited, ouabain-insensitive ATPase, first described by Kasbekar & Durbin (1965) in the frog gastric mucosa, has subsequently been found in a variety of anion-transporting tissues including teleost gills (Kerstetter & Kirschner, 1974;Solomon, Silva, Bend K. J. DEGNAN AND OTHERS & Maetz & Bornancin, 1975). This ATPase has an apparent Km for HCO3-of 16 mm (Kerstetter & Kirschner, 1974) which was the concentration of HCO3-in the Ringer used to bathe the isolated opercular epithelium.…”

“…The HCO3--activated, SCN--inhibited, ouabain-insensitive ATPase, first described by Kasbekar & Durbin (1965) in the frog gastric mucosa, has subsequently been found in a variety of anion-transporting tissues including teleost gills (Kerstetter & Kirschner, 1974;Solomon, Silva, Bend K. J. DEGNAN AND OTHERS & Maetz & Bornancin, 1975). This ATPase has an apparent Km for HCO3-of 16 mm (Kerstetter & Kirschner, 1974) which was the concentration of HCO3-in the Ringer used to bathe the isolated opercular epithelium. Assuming that the intracellular chloride cell HC03-concentration is in equilibrium with the extracellular HCO3-concentration, increasing the latter would lead to an increase in the intracellular HCO3-and an increased activity of the HCO3--activated ATPase. If this enzyme supplied the energy for the active Cl-transport, a stimulation of its activity by HCO3-would explain the influence of this anion on Cl-secretion across the opercular epithelium.…”