Na+ influx-induced decrease of (Na+ + K+)-ATPase activity in rat brain slices: role of Ca2+.
Treatment of rat brain slices with veratrine and monensin decreased (Na+ + K+)-ATPase activity in the membranes in a dose-dependent manner. The effect of monensin, like that of veratrine, was accompanied by a decrease of maximal binding sites for ouabain. The inhibitory effect of monensin on the enzyme activity was dependent on external Ca2+ at low concentrations, but not at a high concentration. The decreased enzyme activity induced by monensin was restored by subsequent incubation of the slices in a Ca(2+)-free medium containing 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester (BAPTA-AM), a chelator of intracellular Ca2+. The effect of monensin at a low concentration on enzyme activity was antagonized by amiloride (1 mM), bepridil (5 microM), quinacrine (30 microM) or verapamil (30 microM), but not by nifedipine (1 microM) or omega-conotoxin (1 microM). Furthermore, the inhibitory effect of monensin at a high concentration under Ca(2+)-free conditions was blocked by BAPTA-AM (30 microM) and by bepridil (100 microM) or diazepam (500 microM), inhibitors of mitochondrial Na(+)-Ca2+ exchange. Inhibitors of calmodulin, protein kinase C, phospholipase A2 and calpain did not affect the monensin-induced decrease of enzyme activity. Dithiothreitol (10 mM) blocked the effect of monensin on enzyme activity but did not affect the ionophore-induced influx of Ca2+ in the slices.
Matsuda
T
T
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Osaka University, Japan.
Shimizu
I
I
Baba
A
A
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D015764:Bepridil / Q000494:pharmacology; D001921:Brain / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002462:Cell Membrane / Q000201:enzymology; D002614:Chelating Agents / Q000494:pharmacology; D003975:Diazepam / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008985:Monensin / Q000494:pharmacology*; D009543:Nifedipine / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D011796:Quinacrine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology; D014702:Veratrine / Q000494:pharmacology*; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D002614:Chelating Agents; D010456:Peptides, Cyclic; D020960:omega-Conotoxins; C053423:Conus magus toxin; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D015764:Bepridil; D000584:Amiloride; D008985:Monensin; D012964:Sodium; D014700:Verapamil; D000254:Sodium-Potassium-Exchanging ATPase; D014702:Veratrine; D011796:Quinacrine; D009543:Nifedipine; D003975:Diazepam; D002118:Calcium