title: Is Ca2+ effect on passive K+ transport mediated by spectrin--dependent ATPase?
abstract: The aim of this report was to find which part of the membrane is responsible for the Ca2+ dependence of membrane permeability to K+. We found that the enzyme activity of large contractile complex of membrane proteins, the so called spectrin-dependent ATPase (sp-ATPase) increases at certain Ca2+ concentrations when K+ permeability decreases and vice versa. Ca2+ apparent dissociation constant for sp-ATPase is 6 X 10(-7) M which is the value corresponding to findings of Porzig and Stoffel (1978) for Ca2+ binding to membrane with low K+ permeability. Moreover, 20 chemically quite different substances which inhibit sp-ATPase activity simultaneously increase in the same concentrations K+ permeability and vice versa. No exception was found. The results show that low membrane permeability to K+ occurs at such conformation of sp-ATPase at which its enzyme activity may fully be manifested whereas at other conformations permeability to K+ increases. The conformation of sp-ATPase seems to affect gating mechanism of a respective channel for passive K+ transport through membrane.
mesh_terms: D000251:Adenosine Triphosphatases / Q000097:blood*; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects; D004910:Erythrocyte Membrane / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D011188:Potassium / Q000097:blood*; D011487:Protein Conformation; D013049:Spectrin / Q000494:pharmacology
chemical_list: D007473:Ion Channels; D013049:Spectrin; D000251:Adenosine Triphosphatases; D011188:Potassium; D002118:Calcium