Heterotrimeric G protein Gi is involved in a signal transduction pathway for ATP release from erythrocytes

Erythrocytes are 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 G(s) resulted in ATP release from erythrocytes. Here we investigate the hypothesis that activation of heterotrimeric G proteins of the G(i) subtype are also involved in a signal transduction pathway for ATP release from rabbit erythrocytes. Heterotrimeric G proteins G(alpha i1), G(alpha i2), and G(alpha i3) but not G(alpha o) were identified in rabbit and human erythrocyte membranes. Pretreatment of rabbit erythrocytes with pertussis toxin (100 ng/ml, 2 h), which uncouples G(i/o) from their effector proteins, inhibited deformation-induced ATP release. Incubation of rabbit and human erythrocytes with mastoparan (Mas, 10 muM) or Mas-7 (1 muM), which are compounds that directly activate G(i) proteins, resulted in ATP release. However, rabbit erythrocytes did not release ATP when incubated with Mas-17 (10 muM), which is an inactive Mas analog. In separate experiments, Mas (10 muM) but not Mas-17 (10 muM) increased intracellular concentrations of cAMP when incubated with rabbit erythrocytes. Importantly, Mas-induced ATP release from rabbit erythrocytes was inhibited after treatment with pertussis toxin (100 ng/ml, 2 h). These data are consistent with the hypothesis that the heterotrimeric G protein G(i) is a component of a signal transduction pathway for ATP release from erythrocytes.