MODELED MICROGRAVITY MODIFIES THE NA{sup}+, K{sup}+ - ATPASE ACTIVITY IN RAT HEART HOMOGENATES

摘要

This study was aimed at establishing whether modeled microgravity conditions, created in a three-dimensional clinostat (Random Positioning Machine, RPM), influence the membrane-associated Na{sup}+, K{sup}+- and Mg{sup}(2+)-ATPase activities in heart homogenates from rats (exposed to RPM for 48 hours). The experimental data indicate that modeled low g significantly decreased the total ATPase (p<0.01) and Na{sup}+, K{sup}+-ATPase activities (p<0.05) with no change of the Mg{sup}(2+)-ATPase activity, compared to the respective rat control groups (ground). This Na{sup}+, K{sup}+-pump inhibition could cause a digitallike effect in response to several modifications of many physiological processes even if this inhibition might also be causally related to the physiological environment induced by RPM. The exact mechanism by which total ATPase and Na{sup}+, K{sup}+-ATPase activities decrease in response to RPM conditions remains to be established. We cannot rule out that a reduced intracellular ATP production, previously demonstrated in other cellular systems submitted to modeled microgravity conditions, could be responsible for the effects reported here.