Fb. Davis et al., INOSITOL PHOSPHATES MODULATE HUMAN RED-BLOOD-CELL CA2-ADENOSINE TRIPHOSPHATASE-ACTIVITY IN-VITRO BY A GUANINE-NUCLEOTIDE REGULATORY PROTEIN(), Metabolism, clinical and experimental, 44(7), 1995, pp. 865-868
D-myo-Inositol 1,4,5-trisphosphate [Ins(1,4,5)P-3] inhibits human red
blood cell (RBC) Ca2+-stimulable, Mg2+-dependent adenosine triphosphat
ase (Ca2+-ATPase) activity in vitro. Because we have previously shown
that adrenergic receptors exist on the human mature RBC membrane and c
an modulate Ca2+-ATPase activity. we examined the possibility that a g
uanine nucleotide regulatory protein (G protein) mediated the Ins(1,4,
5)P-3 effect. Guanosine 5'-O-(3-thiotrisphosphate) (GTP gamma S) 10(-4
) mol/L also inhibited RBC Ca2+-ATPase activity. Pertussis toxin 200 n
g/mL blocked the effects of both Ins(1,4,5)P-3 and GTP gamma S on Ca2-ATPase activity. In separate studies, pertussis toxin-catalyzed adeno
sine diphosphate (ADP) ribosylation was shown to occur in RBC membrane
s under conditions in which measurements of Ca2+-ATPase activity were
performed. When Ins(1,4,5)P-3 10(-7) mol/L and GTP gamma S 10(-6) mol/
L were added to membranes concurrently, their inhibitory actions on th
e enzyme were additive. At greater concentrations of Ins(1,4,5)P-3 (10
(-6) to 10(-5) mol/L) and GTP gamma S (10(-4) mol/L), the inositol pho
sphate reversed the inhibitory effect of GTP gamma S. These observatio
ns indicate that the novel effect of Ins(1,4,5)P-3 on the activity of
a plasma membrane Ca2+-ATPase depends at least in part on the action o
f a pertussis toxin-susceptible G protein. Copyright (C) 1995 by W.B.
Saunders Company