title: [Biochemical demonstration of HCO3--und Cl--dependent ATPase activities in the rectum of larval dragonflies and inhibition of rectal chloride uptake by thiocyanate (author's transl)].
abstract: Hydrogencarbonate and chloride activated, ouabain-insensitive ATPase activities are demonstrated in the salt-absorbing rectum of larval dragonflies. Maximal activation is achieved at approx. 30 mM HCO3- and 20 mM Cl-, respectively. The stimulation of each anion obeys Michaelis-Menten kinetics Km values are 4.65 mM for HCO3-- and 10.25 mM for Cl--activation. The activating anion of one type of ATPase simultaneously exerts an inhibitory effect on the other. Cl--activation is also reduced by Mg.ATP in concentrations above 0.5 mM and by Tris-Hepes buffer exceeding 2.5 mM. Both anion-dependent ATPase activities are found enriched in subcellular membraneous fractions of the rectum. Thiocyanate inhibits both activities and causes a significant decrease in rectal uptake of radioactive chloride from hypo-osmotic external solution. In the case of HCO3- dependent ATPase a competitive inhibition as SCN- was found with an inhibitor constant of Ki=0.5 mM.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D002712:Chlorides / Q000378:metabolism* / Q000494:pharmacology; D007313:Insecta / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D012007:Rectum / Q000378:metabolism; D013861:Thiocyanates / Q000494:pharmacology*
chemical_list: D001639:Bicarbonates; D002712:Chlorides; D013861:Thiocyanates; D000251:Adenosine Triphosphatases
vernacular_title: Biochemischer Nachweis von CHO3-- und Cl--abhängigen ATPase-Aktivitäten im Rectum von anisopteren Libellenlarven und Hemmung der rectalen Chloridaufnahme durch Thiocyanat.