The role of G protein beta subunits in the release of ATP from human erythrocytes.

Previously, we demonstrated that adenosine triphosphate (ATP) is released from human erythrocytes in response to mechanical deformation and that this release requires activation of a signal-transduction pathway involving adenylyl cyclase and the heterotrimeric G protein, Gs. Here we investigate the role of heterotrimeric G proteins of the Gi subtype in the release of ATP from human erythrocytes. In addition, we determined the profile of heterotrimeric G protein beta subunits present in these erythrocyte membranes. The activity of Gi was stimulated by incubation of erythrocytes (20% hematocrit) with mastoparin (10 microM). ATP release was measured using the luciferin/luciferase assay. Heterotrimeric G protein beta subunits present in erythrocyte membranes were resolved using gel electrophoresis and subunit specific antibodies. Incubation of human erythrocytes with mastoparan (an activator of Gi/o) resulted in a 4.1 +/- 0.6-fold increase in ATP present in the medium (P<0.01). Human erythrocyte membranes stain positively for beta subunit types 1, 2, 3 and 4, all of which been reported to activate of some isoforms of adenylyl cyclase. Activation of the heterotrimeric G protein, Gi, results in ATP release from erythrocytes. This effect is may be related to the activity of beta subunits associated with this G protein in the human erythrocyte.