Inhibition of NHE protects reoxygenated cardiomyocytes independently of anoxic [Ca.sup.2+] overload and acidosis

Schafer, C., Y. V. Ladilov, M. Schafer, and H. M. Piper. Inhibition of NHE protects reoxygenated cardiomyocytes independently of anoxic [Ca.sup.2+] overload and acidosis. Am J Physiol Heart Circ Physiol 279: H2143-H2150, 2000.--We investigated the question of whether inhibition of the [Na.sup.+]/[H.sup.+] exchanger (NHE) during ischemia is protective due to reduction of cytosolic [Ca.sup.2+] accumulation or enhanced acidosis in cardiomyocytes. Additionally, the role of the [Na.sup.+]-[MATHEMATHICAL EXPRESSION] symporter (NBS) was investigated. Adult rat cardiomyocytes were exposed to simulated ischemia and reoxygenation. Cytosolic pH [2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF)], [Ca.sup.2+] (fura 2), [Na.sup.+] [sodium-binding benzolfuran isophthatlate (SBFI)], and cell length were measured. NHE was inhibited with 3 [Mu]mol/l HOE 642 or 1 [Mu]mol/l 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), and NBS was inhibited with HEPES buffer. During anoxia in bicarbonate buffer, cells developed acidosis and intracellular Na and Ca ([Na.sub.i] and [Ca.sub.i], respectively) overload. During reoxygenation cells underwent hypercontracture (44.0 [+ or -] 4.1% of the preanoxic length). During anoxia in bicarbonate buffer, inhibition of NHE had no effect on changes in intracellular pH ([pH.sub.i]), [Na.sub.i], and [Ca.sub.i], but it significantly reduced the reoxygenation-induced hypercontracture (HOE: 61.0 [+ or -] 1.4%, EIPA: 68.2 [+ or -] 1.8%). The sole inhibition of NBS during anoxia was not protective. We conclude that inhibition of NHE during anoxia protects cardiomyocytes against reoxygenation injury independently of cytosolic acidification and [Ca.sub.i] overload. hypercontracture; pH control; calcium; sodium-hydrogen exchanger