ATPHASE CONTENT OF STRIATED MUSCLE STRESSED IN O2/CO2 AND HYPERBARIC N2/O2/CO2 ATMOSPHERES

The ATPase content of diaphragm tissue from the rat has been measured as a function of exposure of the innervated diaphragm preparation, working in isometric mode, to 95% O2 5% CO2 and N2/O2/CO2 hyperbaric gaseous atmospheres. With the former gas mixture employed at atmospheric pressure, no ATPase is lost from muscle following 30 min of vigorous work at a mean neural stimulus frequency of 23.8 Hz. With N2-containing atmospheres at CO2 levels of 1, 3, and 5% and at total pressures ranging from ambient to 215 psia, the muscle ATPase content of tissue, worked at a modest rate of 0.15 twitch response per second, remains sensibly constant over virtually the entire spread of pressure and CO2 levels employed. Only in experiments which combine very low total pressure and partial pressure of CO2, or very high values of these two stressing parameters, does the ATPase content per unit weight of diaphragm muscle dip slightly below the control level for unworked tissue. Therefore, moderate hyperbaric stress and CO2 exposure do not deprive this working tissue of its vital ATPase content, in contrast with its known propensity toward easy in vitro loss of glycolytic enzymes, adenylic acid deaminase, etc. © 1969.