Gi and ATP release from erythrocytes

Erythrocytes have been reported to release ATP in response to mechanical deformation and decreased oxygen tension. Previously, we proposed that receptor-mediated activation of the heterotrimeric G protein, Gs, resulted in ATP release from erythrocytes. Here we investigate the hypothesis that activation of heterotrimeric G proteins of the Gi subtype are also involved in a signal transduction pathway for ATP release from rabbit erythrocytes. Heterotrimeric G proteins Gαi1, Gαi2 and Gαi3, but not Gαo were identified in rabbit and human erythrocyte membranes. Pre-treatment of rabbit erythrocytes with pertussis toxin (100ng/ml, 2h), which uncouples Gi/o from their effector proteins, inhibited deformation-induced ATP release. Incubation of rabbit and human erythrocytes with mastoparan (10 µM) or mastoparan 7 (1 µM), compounds that directly activate Gi proteins, resulted in ATP release. However, rabbit erythrocytes did not release ATP when incubated with mastoparan 17 (10 µM), an inactive mastoparan analog. In separate experiments, mastoparan (10 µM), but not mastoparan 17 (10 µM), increased intracellular concentrations of cAMP when incubated with rabbit erythrocytes. Importantly, mastoparan-induced ATP release from rabbit erythrocytes was inhibited after treatment with pertussis toxin (100ng/ml, 2h). These data are consistent with the hypothesis that the heterotrimeric G protein Gi, is a component of a signal-transduction pathway for ATP release from erythrocytes.