Negative regulation of the platelet Na+/H+ exchanger by trimeric G-proteins.
Human platelets contain a Na+/H+ exchanger (NHE) that regulates the cytosolic pH. The role of trimeric G-proteins in NHE control was investigated in plasma membrane vesicles by measuring exchange of intravesicular protons for extravesicular Na+. Exchange was saturable, independent of membrane potential and inhibited by ethylisopropyl amiloride (Ki 0.05 micromol.L-1), demonstrating the involvement of NHE-1. The G-protein activators AlF4- and GMP-P(NH)P reduced exchange by increasing the Km for Na+ from 11.3 +/- 2.1 mM to 21.6 +/- 1.4 mM (AlF4-) and 19.8 +/- 1.1 mM (GMP-P(NH)P), leaving Vmax and the Hill coefficient unchanged. This effect was abolished by inhibitors of Gi-proteins (N-ethylmaleimide, holoenzyme- and A-protomer of pertussis toxin) and by an anti-Galpha Ig and GDP(beta)S. Activation of Gi-proteins by mastoparan and its synthetic analogue Mas7 also strongly reduced NHE activity. These data show that in platelets NHE-1 is under negative control of the Gi-family of trimeric G-proteins.
van Willigen
G
G
Department of Haematology, Laboratory for Thrombosis and Haemostasis, University Medical Center Utrecht, The Netherlands. g.vanwilligen@lab.azu.nl
Nieuwland
R
R
Nürnberg
B
B
Gorter
G
G
Akkerman
J W
JW
D000165:Acridine Orange; D002462:Cell Membrane / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
D017923:Sodium-Hydrogen Exchangers; D019204:GTP-Binding Proteins; D000165:Acridine Orange