Platelet shape change and protein phosphorylation induced by ADP and thrombin are not sensitive to short periods of microgravity.

Recent experiments have shown that the stimulation of animal cells in vitro by direct protein kinase C (PKC) activators is significantly reduced under microgravity (micro g). Platelets undergo protein phosphorylation and morphological changes a few seconds after stimulation by agonists such as phorbol esters which activate PKC. Therefore, taking advantage of parabolic plane flight to obtain short periods of microgravity, we studied phosphorylation of myosin light chain (20K), specific PKC-dependent phosphorylation of a 40,000 M(r) protein, pleckstrin (40K) and platelet shape change. SDS-PAGE analysis and electron microscopy were performed on platelets subjected to 20 seconds microgravity as compared to normal gravity (1 g) conditions. These investigations showed that neither Ca(2+)-calmodulin-mediated activation nor the PKC-dependent pathways are inhibited during short periods of microgravity.