Stimulation of Xenopus oocyte Na(+),K(+)ATPase by the serum and glucocorticoid-dependent kinase sgk1.
The serum and glucocorticoid-dependent kinase-1 (sgk1) is expressed in a wide variety of tissues including renal epithelial cells. As it is up-regulated by aldosterone, it is considered to participate in the regulation of renal Na(+) reabsorption. Indeed, co-expression of sgk1 with the renal epithelial Na(+) channel (ENaC) augments Na(+) channel activity. The aim of the present study was to examine possible effects of sgk1 on Na(+)/K(+)-ATPase activity. To this end dual-electrode voltage-clamp experiments were performed in Xenopus oocytes expressing the active kinase (S422D)sgk1 or the inactive mutant (K127N)sgk1. Na(+)/K(+)-ATPase activity was estimated from the hyperpolarization (delta V(m)) and the outwardly-directed current ( I(P)) created by addition of extracellular K(+) in the presence of K(+) channel blocker Ba(2+). Both delta V(m) and I(P) were significantly larger in oocytes expressing (S422D)sgk1 than in those expressing (K127N)sgk1 or having been injected with water. I(P) was fully inhibited by ouabain. Ion-selective microelectrodes showed that the stimulation of pump current was not the result of altered cytosolic Na(+) activity or pH. The present results thus point to an additional action of sgk1 that may participate in the regulation of renal tubular Na(+) transport. Moreover, sgk1 may be involved in the regulation of Na(+)/K(+)-ATPase in extrarenal tissues.
Physiologisches Institut, Universität Tübingen, Gmelinstrasse 5, 72076 Tübingen, Germany.
Iwan
I
Setiawan
Guido
G
Henke
Yuxi
Y
Feng
Christoph
C
Böhmer
Larisa A
LA
Vasilets
Wolfgang
W
Schwarz
Florian
F
Lang
D000450:Aldosterone / Q000378:metabolism; D000818:Animals; D004594:Electrophysiology; D017874:Immediate-Early Proteins; D008564:Membrane Potentials / Q000502:physiology; D016296:Mutagenesis / Q000502:physiology; D009687:Nuclear Proteins; D009865:Oocytes / Q000201:enzymology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014981:Xenopus; D000099184:Serum-Glucocorticoid Regulated Kinases
D000450:Aldosterone; D017874:Immediate-Early Proteins; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases; D000254:Sodium-Potassium-Exchanging ATPase; D000099184:Serum-Glucocorticoid Regulated Kinases