title: Digitalis-induced cell signaling by the sodium pump: on the relation of Src to Na(+)/K(+)-ATPase.
abstract: In addition to performing its essential transport function, the sodium pump also activates multiple cell signaling pathways in response to digitalis drugs such as ouabain. Based mainly on cell-free studies with mixtures of purified Src kinase and Na(+)/K(+)-ATPase, a well-advocated hypothesis on how ouabain initiates the activation of signaling pathways is that there is a preexisting physiological complex of inactive Src bound to the α-subunit of Na(+)/K(+)-ATPase, and that ouabain binding to this subunit disrupts the bound Src and activates it. Because of the published disagreements of the results of such cell-free experiments of two other laboratories, our aim was to attempt the resolution of these discrepancies. We reexamined the effects of ouabain, vanadate, and oligomycin on mixtures of Src, Na(+)/K(+)-ATPase, Mg(2+), and ATP as specified in prior studies; and assayed for Src-418 autophosphorylation as the measure of Src activation. In contrast to the findings of the proponents of the above hypothesis, our results showed similar effects of the three inhibitors of Na(+)/K(+)-ATPase; indicating that Src activation in such experiments is primarily due to the ATP-sparing effect of the ATPase inhibitor on the mixture of two enzymes competing for ATP. We conclude that there is no solid evidence for direct molecular interaction of Src with Na(+)/K(+)-ATPase under physiological conditions.
authors.affiliation: Department of Biochemistry and Cancer Biology, College of Medicine and Life Sciences, University of Toledo, Health Science Campus, Toledo, OH 43614, USA.
authors.forename: Marjorie E
authors.initials: ME
authors.lastname: Gable
authors.affiliation: Department of Physiology and Pharmacology and the Center for Diabetes and Endocrine Research, University of Toledo, Health Science Campus, Toledo, OH 43614, USA.
authors.forename: Simon L
authors.initials: SL
authors.lastname: Abdallah
authors.affiliation: Department of Physiology and Pharmacology and the Center for Diabetes and Endocrine Research, University of Toledo, Health Science Campus, Toledo, OH 43614, USA.
authors.forename: Sonia M
authors.initials: SM
authors.lastname: Najjar
authors.affiliation: Department of Biochemistry and Cancer Biology, College of Medicine and Life Sciences, University of Toledo, Health Science Campus, Toledo, OH 43614, USA.
authors.forename: Lijun
authors.initials: L
authors.lastname: Liu
authors.affiliation: Department of Biochemistry and Cancer Biology, College of Medicine and Life Sciences, University of Toledo, Health Science Campus, Toledo, OH 43614, USA. Electronic address: amir.askari@utoledo.edu.
authors.forename: Amir
authors.initials: A
authors.lastname: Askari
mesh_terms: D000818:Animals; D004070:Digitalis / Q000737:chemistry; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D009840:Oligomycins / Q000494:pharmacology*; D010042:Ouabain / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D021122:Protein Subunits / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013552:Swine; D014638:Vanadates / Q000494:pharmacology*; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D009840:Oligomycins; D021122:Protein Subunits; D014638:Vanadates; D010042:Ouabain; D019061:src-Family Kinases; D000254:Sodium-Potassium-Exchanging ATPase
keywords: Na(+)/K(+)-ATPase; Oligomycin; Ouabain; Signaling; Src; Vanadate