Anion-stimulated ATPase in locust rectal epithelium

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Abstract
The rectum, the main reabsorptive site in the locust excretory system, actively transport Cl-. This Cl- absorption is electrogenic, not dependent on Na+ or HCO3-/CO2, and insensitive to inhibitors of NaCl cotransport or HCO3-/Cl- exchange. To determine if active Cl- transport across rectal epithelia might be due to an anion-stimulated ATPase, a microsomal fraction was obtained by differential centrifugation. Microsomal ATPase activity was stimulated in the following sequence: sulphite > bicarbonate > chloride. Maximal ATPase activity was obtained at 25 mM HCO3- or 25 mM Cl-. Thiocyanate (10 mM) inhibited 90% of the anion-stimulated ATPase activity. The microsomal fraction was enriched in the plasma membrane markers, leucine aminopeptidase, alkaline phosphatase, 5''-nucleotidase, and .gamma.-glutamyltranspeptidase, and had little contamination of the mitochondrial enzymes, succinate cytochrome c reductase and cytochrome oxidase. Na,K-ATPase was enriched in the mitochondrial fraction. Microscopic examination confirmed that basolateral membranes were associated with mitochondria following differential centrifugation, while the microsomal fraction contained little mitochondrial contamination. These resutls indicate the presence of an anion-stimulated ATPase activity that could be responsible for active Cl- transport across locust recta.