title: Protection of reoxygenated cardiomyocytes against hypercontracture by inhibition of Na+/H+ exchange.
abstract: Effects of Na+/H+ exchange inhibition and cytosolic acidosis on reoxygenated adult rat ventricular cardiomyocytes were investigated. Cells were incubated in anoxic media at pH 6.4 until pCa of < or = 5, intracellular pH (pHi) of 6.5, and cytosolic [Na+] of 50 mM were reached. On reoxygenation, medium pH was changed to 7.4 to activate Na+/H+ exchange. In one group, 20 microM HOE-694, an inhibitor of Na+/H+ exchange, was added. With or without HOE-694, cytosolic Ca2+ and Na+ returned to control levels within 10 min of reoxygenation. In the absence of HOE-694, the pHi renormalized (to 7.2) within 8 min, but irreversible hypercontracture and transient Ca2+ oscillations were observed. In the presence of HOE-694, pHi stayed acidotic (at 6.5), hypercontracture was prevented, and Ca2+ oscillations were attenuated. When the Na+ pump was inhibited with 0.1 mM ouabain, even partial recovery of Ca2+ control became impossible unless HOE-694 was added. Our conclusions are 1) activation of Na+/H+ exchange does not impair recovery of cytosolic Na+ and Ca2+ control unless activity of the sarcolemmal Na+ pump is critically reduced, and 2) due to prolongation of cytosolic acidosis, inhibition of Na+/H+ exchange protects against reoxygenation-induced hypercontracture and cytosolic Ca2+ oscillations.
authors.affiliation: Physiologisches Institut, Justus-Liebig-Universität, Giessen, Germany.
authors.forename: Y V
authors.initials: YV
authors.lastname: Ladilov
authors.forename: B
authors.initials: B
authors.lastname: Siegmund
authors.forename: H M
authors.initials: HM
authors.lastname: Piper
mesh_terms: D000818:Animals; D003600:Cytosol / Q000378:metabolism; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006146:Guanidines / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008297:Male; D009200:Myocardial Contraction; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010100:Oxygen / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism; D013450:Sulfones / Q000494:pharmacology
chemical_list: D005452:Fluoresceins; D005456:Fluorescent Dyes; D006146:Guanidines; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; C074107:3-methylsulfonyl-4-piperidinobenzoyl guanidine; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D010100:Oxygen