Some experiments on ouabain-sensitiveness of 22Na efflux and availability of exogenous adenosine triphosphate in the muscle fibre membrane.

It has been proposed that sodium ions of the muscle cells are present ii'' their outer regions and the major portion of an outward movement of sodium ions across the membrane of the striated muscles is accounted for an active transport which is dependent on sodium pump activity sensitive to cardiac glycosides (Mullins and Frumento, 1963 ; Csaky, 1965 ; Horowicz and Gerber ). A previous paper by the present author (Noda, 1968 indicated that susceptibility of the pumping-out activity of 22Na ions to ouabain was related to the metabolic level, intracellular or membranous, and this phenomenon was not explained in terms of decalcification from the cell membrane. At present, of course, the problem is still unclear of how cellular metabolism connects with an active transport process of Na or K ions. The experiments described here have been carried out in an attempt to find an answer to the question that does the membrane metabolism yielding energy through dephosphorylation of adenosine triphosphate (ATP) act directly on sodium pump activity to maintain the excitability of the cell or does the active transport require certain macromolecular skeleton of lipoprotein in the membranes of which structural establishment is probably achieved by divalent Ca ions ; in other words, the experiments have been performed to observe ionic kinetics across the membrane of the muscles which were . treated with ouabain or to know the conformational changes of the membrane which allow to occur the effects of ouabain. In particular, it has been attempted to decide (1) whether Na efflux from the depolarized sartorius muscles includes a ouabain-sensitive component, (2) whether the metabolism-dependent Na outflux has any relation to withdrawal of Ca ions from the cell surface, (3) whether Na pump system consisting mainly of ATPase which is inhibited by ouabain can use exogenous ATP as its energy source, or (4) whether lipolysis or proteolysis of the muscle membrane has any relation to ouabain-sensitive Na efflux.