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1 Department of Pharmacology, Department of Physiology and Cell Biology, Center for Biomedical Research Excellence, University of Nevada School of Medicine, RENO, NV, USA
* To whom correspondence should be addressed. E-mail: yambo{at}med.unr.edu.
The serum and glucocorticoid-inducible kinase (SGK) is a serine/threonine protein kinase transcriptionally regulated by corticoids, serum and cell volume. SGK regulates cell volume of various cells by effects on Na+ and K+ transport through membrane channels. We hypothesized a role for SGK in the activation of volume sensitive osmolyte and anion channels (VSOACs) in cultured canine pulmonary artery smooth muscle cells (PASMCs). Intracellular dialysis through the patch electrode of recombinant active SGK, but not kinase-dead
60-SGK-K127M, heatinactivated SGK or active Akt1, partially activated VSOACs under isotonic conditions. Dialysis
of active SGK prior to cell exposure to hypotonic medium significantly accelerated the activation kinetics and increased the maximal density of VSOAC current. Exposure of PASMCs to hypotonic medium (230 mOsm) activated phosphatidylinositol 3-kinases (PI3Ks) and their
downstream targets Akt/PKB and SGK, but not PKC
. Inhibition of PI3Ks with wortmannin reduced the activation rate and maximal amplitude of VSOACs. Immunoprecipitated ClC-3 channels were phosphorylated by PKC
but not by SGK in vitro, suggesting SGK may activate
VSOACs indirectly. These data indicate that the PI3K-SGK cascade is activated upon hypotonic swelling of PASMCs, and in turn affects downstream signaling molecules linked to activation of VSOACs.
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