Inositol phosphates modulate human red blood cell Ca(2+)-adenosine triphosphatase activity in vitro by a guanine nucleotide regulatory protein.

D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] inhibits human red blood cell (RBC) Ca(2+)-stimulable, Mg(2+)-dependent adenosine triphosphatase (Ca(2+)-ATPase) activity in vitro. Because we have previously shown that adrenergic receptors exist on the human mature RBC membrane and can modulate Ca(2+)-ATPase activity, we examined the possibility that a guanine nucleotide regulatory protein (G protein) mediated the Ins(1,4,5)P3 effect. Guanosine 5'-O-(3-thiotrisphosphate) (GTP gamma S) 10(-4) mol/L also inhibited RBC Ca(2+)-ATPase activity. Pertussis toxin 200 ng/mL blocked the effects of both Ins(1,4,5)P3 and GTP gamma S on Ca(2+)-ATPase activity. In separate studies, pertussis toxin-catalyzed adenosine diphosphate (ADP) ribosylation was shown to occur in RBC membranes under conditions in which measurements of Ca(2+)-ATPase activity were performed. When Ins(1,4,5)P3 10(-7) mol/L and GTP gamma S 10(-6) mol/L were added to membranes concurrently, their inhibitory actions on the enzyme were additive. At greater concentrations of Ins(1,4,5)P3 (10(-6) to 10(-5) mol/L) and GTP gamma S (10(-4) mol/L), the inositol phosphate reversed the inhibitory effect of GTP gamma S. These observations indicate that the novel effect of Ins(1,4,5)P3 on the activity of a plasma membrane Ca(2+)-ATPase depends at least in part on the action of a pertussis toxin-susceptible G protein.