title: Platelet-activating factor stimulates sodium-hydrogen exchange in ventricular myocytes.
abstract: Sodium-hydrogen exchanger (NHE), the principal sarcolemmal acid extruder in ventricular myocytes, is stimulated by a variety of autocrine/paracrine factors and contributes to myocardial injury and arrhythmias during ischemia-reperfusion. Platelet-activating factor (PAF; 1-o-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a potent proinflammatory phospholipid that is released in the heart in response to oxidative stress and promotes myocardial ischemia-reperfusion injury. PAF stimulates NHE in neutrophils and platelets, but its effect on cardiac NHE (NHE1) is unresolved. We utilized quiescent guinea pig ventricular myocytes bathed in bicarbonate-free solutions and epifluorescence to measure intracellular pH (pH(i)). Methylcarbamyl-PAF (C-PAF; 200 nM), a metabolically stable analog of PAF, significantly increased steady-state pH(i). The alkalosis was completely blocked by the NHE inhibitor, cariporide, and by sodium-free bathing solutions, indicating it was mediated by NHE activation. C-PAF also significantly increased the rate of acid extrusion induced by intracellular acidosis. The ability of C-PAF to increase steady-state pH(i) was completely blocked by the PAF receptor inhibitor WEB 2086 (10 μM), indicating the PAF receptor is required. A MEK inhibitor (PD98059; 25 μM) also completely blocked the rise in pH(i) induced by C-PAF, suggesting participation of the MAP kinase signaling cascade downstream of the PAF receptor. Inhibition of PKC with GF109203X (1 μM) and chelerythrine (2 μM) did not significantly affect the alkalosis induced by C-PAF. In summary, these results provide evidence that PAF stimulates cardiac NHE1, the effect occurs via the PAF receptor, and signal relay requires participation of the MAP kinase cascade.
authors.affiliation: Nora Eccles Harrison Cardiovascular Research and Training Institute, Salt Lake City, Utah, USA.
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Ajiro
authors.forename: Noriko
authors.initials: N
authors.lastname: Saegusa
authors.forename: Wayne R
authors.initials: WR
authors.lastname: Giles
authors.forename: Diana M
authors.initials: DM
authors.lastname: Stafforini
authors.forename: Kenneth W
authors.initials: KW
authors.lastname: Spitzer
mesh_terms: D000138:Acidosis / Q000378:metabolism; D000471:Alkalosis / Q000378:metabolism; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D053119:Benzophenanthridines / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005419:Flavonoids / Q000494:pharmacology; D006146:Guanidines / Q000494:pharmacology; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007211:Indoles / Q000494:pharmacology; D017136:Ion Transport; D008301:Maleimides / Q000494:pharmacology; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D010742:Phospholipid Ethers / Q000494:pharmacology; D010972:Platelet Activating Factor / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins / Q000187:drug effects / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D043562:Receptors, G-Protein-Coupled / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013450:Sulfones / Q000494:pharmacology; D013997:Time Factors; D014230:Triazoles / Q000494:pharmacology
chemical_list: D001381:Azepines; D053119:Benzophenanthridines; D005419:Flavonoids; D006146:Guanidines; D007211:Indoles; D008301:Maleimides; D010742:Phospholipid Ethers; D010972:Platelet Activating Factor; D010980:Platelet Membrane Glycoproteins; D047428:Protein Kinase Inhibitors; D043562:Receptors, G-Protein-Coupled; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; D014230:Triazoles; C039351:platelet activating factor receptor; C052518:WEB 2086; C053479:1-O-hexadecyl-2-N-methylcarbamylphosphatidylcholine; C093373:cariporide; D012964:Sodium; C016299:chelerythrine; D011493:Protein Kinase C; D020929:Mitogen-Activated Protein Kinase Kinases; C070515:bisindolylmaleimide I; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one