G protein regulation of the Na+/H+ antiporter in Xenopus laevis oocytes. Involvement of protein kinases A and C.
We have characterized the regulation of the endogenous Na+/H+ exchanger in Xenopus laevis oocytes by G proteins and protein kinases by measuring the ethylisopropylamiloride-sensitive Li+ uptake. Injection of oocytes with the stable GTP analog GTP gamma S stimulated Li+ uptake up to almost 4-fold, an effect blocked by coinjection with the GDP analog, guanyl-5'-yl thiophosphate. Injection into oocytes of beta gamma subunits of the heterotrimeric G protein transducin enhanced Li+ uptake by about 3-fold. This stimulation was blocked by transducin alpha subunits, which by themselves did not influence Li+ uptake. Using various activators and inhibitors of protein kinases, it is demonstrated that the X. laevis oocyte Na+/H+ antiporter can be stimulated by activation of both protein kinase A and C. Stimulation of Na+/H+ exchanger activity by GTP gamma S but not that induced by transducin beta gamma subunits was blocked by the protein kinase A inhibitor H-89. On the other hand, transducin beta gamma subunit-stimulated activity was prevented by the protein kinase C inhibitor, calphostin C. The non-selective protein kinase inhibitor H-7 blocked both GTP gamma S- and transducin beta gamma subunit-stimulated Na+/H+ exchanger activity. The results suggest that the Na+/H+ exchanger of X. laevis oocytes can be activated by G proteins and that this activation is not direct but mediated by protein kinase A- and/or protein kinase C-dependent pathways.
Busch
S
S
Institut für Pharmakologie, Universität GH Essen, Germany.
Wieland
T
T
Esche
H
H
Jakobs
K H
KH
Siffert
W
W
D000818:Animals; D001483:Base Sequence; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017931:DNA Primers; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006150:Guanine Nucleotides / Q000378:metabolism; D008094:Lithium / Q000378:metabolism; D008969:Molecular Sequence Data; D009865:Oocytes / Q000201:enzymology / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D014982:Xenopus laevis
D017931:DNA Primers; D006150:Guanine Nucleotides; D017923:Sodium-Hydrogen Exchangers; D008094:Lithium; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D019204:GTP-Binding Proteins