Thiocyanate inhibition of ATPase and its relationship to anion transport

Abstract

Adenosine triphosphatase activity not dependent on sodium or potassium but inhibited by thiocyanate is present in broken-cell homogenates of eel gill and rat kidney. This enzymatic property is predominantly associated with mitochondria, although thiocyanate-inhibited ATPase can also be detected in microsomes with little or no mitochondrial contamination as measured by the activity of the mitochondrial marker enzyme succinic dehydrogenase. When eels are transferred from fresh to salf water, thus increasing active outward transport of chloride across the gill, the thiocyanate-inhibited ATPase of gill microsomes does not change, though the activities of succinic dehydrogenase and Na-K-ATPase in gill homogenates are augmented. The thiocyanate-inhibited ATPase of homogenates of outer renal medulla does not differ from that of renal cortex, in contrast to Na-k-atpase which is higher in renal medulla than in cortex. The data do not support a role for thiocyanate-inhibited ATPase in active chloride transport by epithelial tissues.

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

“…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.…”

“…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.…”

Temperature, photoperiod, and water–electrolyte balance in rainbow trout, Salmo gairdneri

“…Although a number of enzyme systems have been implicated in branchial electrolyte uptake by freshwater teleosts (Maetz 1974) there is presently little support for the earlier hypothesis that a (HC0,-)-stimulated analogue of the (Na' :K+)ATPase system plays any significant role in chloride recruitment (Kerstetter andKirschner 1972, 1974;Solomon et al 1975;McCarty and Houston 1977). There can be little doubt, on the other hand, as to the involvement of (Naf :K+)ATPase in sodium uptake (Maetz 1974).…”