title: Phorbol diacetate potentiates na(+)-k(+) ATPase inhibition by a putative endogenous ligand, marinobufagenin.
abstract: Several vasoconstrictor agents can regulate the phosphorylation status of the Na(+)-K(+) ATPase (NKA). We have recently demonstrated that mammalian tissues contain an endogenous bufadienolide, digitalis-like alpha(1)-NKA-selective ligand, marinobufagenin (MBG). Protein kinase C induces phosphorylation of the alpha(1)-NKA isoform, the major isoform in vascular smooth muscle, kidney, and heart cells. We hypothesized that protein kinase C-induced phosphorylation of NKA can potentiate the effect of endogenous digitalis-like ligands, and that such potentiation can occur in an NKA isoform-specific fashion. A protein kinase C activator, phorbol 12,13-diacetate (PDA, 50 nmol/L), induced phosphorylation of the alpha1-NKA from human mesenteric artery (HMA) sarcolemma and rat kidney but not that of the alpha(3)-NKA from rat fetal brain. In HMA sarcolemma, which predominantly contains alpha(1)-NKA, PDA (50 nmol/L) potentiated the NKA-inhibitory effect of MBG at the level of high-affinity binding sites (0.05 +/- 0.03 nmol/L versus 4.0 +/- 1.7 nmol/L, P<0.05). In contrast, PDA did not affect the NKA inhibition by ouabain, an alpha(3)-NKA ligand. In isolated endothelium-denuded HMA artery rings, 50 nmol/L PDA potentiated the MBG-induced vasoconstriction (EC(50), 17 +/- 6 nmol/L versus 150 +/- 40 nmol/L; P<0.01). Our results suggest that alpha(1)-isoform-specific NKA inhibition by the endogenous digitalis-like ligand, MBG, is substantially enhanced via NKA phosphorylation by protein kinase C. Thus, an interaction of protein kinase C-dependent phosphorylation and MBG on NKA activity may underlie the synergistic vasoactive effects of MBG and other endogenous vasoconstrictors in hypertension.
authors.affiliation: Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA.
authors.forename: Olga V
authors.initials: OV
authors.lastname: Fedorova
authors.forename: Natalia A
authors.initials: NA
authors.lastname: Dorofeeva
authors.forename: Denis A
authors.initials: DA
authors.lastname: Lopatin
authors.forename: Edward G
authors.initials: EG
authors.lastname: Lakatta
authors.forename: Alexei Y
authors.initials: AY
authors.lastname: Bagrov
mesh_terms: D000818:Animals; D001921:Brain / Q000187:drug effects / Q000196:embryology / Q000201:enzymology; D002018:Bufanolides / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007668:Kidney / Q000187:drug effects / Q000201:enzymology; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects / Q000201:enzymology / Q000502:physiology; D008875:Middle Aged; D010042:Ouabain / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology*; D051381:Rats; D012508:Sarcolemma / Q000187:drug effects / Q000201:enzymology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: D002018:Bufanolides; D004791:Enzyme Inhibitors; D010703:Phorbol Esters; C008874:phorbol-12,13-diacetate; C093896:marinobufagenin; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase