Modeled microgravity modifies the Na+, K+-ATPase activity in rat heart homogenates

This study was aimed at establishing whether modeled microgravity conditions, created in a three-dimensional c1inostat (Random Positioning Machine, RPM), influ- ence the membrane-associated Na+, K+- and Mg2+- ATPase activities in heart homogenates from rats (ex- posed to RPM for 48 hours). The experimental data in- dicate that modeled low g significantly decreased the total ATPase (p<O.OI) and Na+, K+ -ATPase activities (p<0.05) with no change of the Mg2+-ATPase activity, compared to the respective rat contro I groups (ground). This Na+, K+- pump inhibition could cause a digital- like effect in response to several modifications of many physiological processes even if this inhibition might also be causally related to the physiological environ- ment induced by RPM. The exact mechanism by which total A TPase and Na +, K+ -A TPase activities decrease in response to RPM conditions remains to be estab- lished. We cannot mie out that a reduced intracellular A TP production, previously demonstrated in other cel- lular systems submitted to modeled microgravity con- ditions, could be responsible for the effects reported here.