Effects of detergents on Na+ + K+-dependent ATPase activity in plasma-membrane fractions prepared from frog muscles. Studies of insulin action on Na+ and K+ transport.
The increase in Na+/K+ transport activity in skeletal muscles exposed to insulin was analysed. Plasma-membrane fractions were prepared from frog (Rana catesbeiana) skeletal muscles, and examination of the Na,K-ATPase (Na+ + K+-dependent ATPase) activity showed that it was insensitive to ouabain. In contrast, plasma-membrane fractions prepared from ouabain-pretreated muscles, by the same procedures, showed extremely low Na,K-ATPase activity. On adding saponin to the membrane suspension, the Na,K-ATPase activity increased, according to the detergent concentration. The maximum activity was about twice the control value, at 0.33 mg of saponin/mg of protein. Thus saponin makes vesicle membranes leaky, allowing ouabain in assay solutions to reach receptors on the inner surface of vesicles. Addition of insulin to saponin-treated membrane suspensions had no effect on the Na,K-ATPase activity, whereas the maximum activity of Na,K-ATPase in whole muscles was stimulated by exposure to insulin. The results show that the stimulation of Na+/K+ transport by insulin is not directly due to insulin binding to receptors on the cell surface, but rather support the view that the increase in the Na,K-ATPase induced by insulin requires an alteration of intracellular events.
Omatsu-Kanbe
M
M
Department of Physiology, Shiga University of Medical Science, Ohtsu, Japan.
Kitasato
H
H
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D003902:Detergents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D009132:Muscles / Q000187:drug effects / Q000201:enzymology*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D011892:Rana catesbeiana; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013501:Surface-Active Agents / Q000494:pharmacology*
D003902:Detergents; D007328:Insulin; D013501:Surface-Active Agents; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium