Protective Effect of HOE642, a Selective Blocker of Na+‐H+ Exchange, Against the Development of Rigor Contracture in Rat Ventricular Myocytes

The objective of this study was to investigate the effect of Na+‐H+ exchange (NHE) and HCO3−‐Na+ symport inhibition on the development of rigor contracture. Freshly isolated adult rat cardiomyocytes were subjected to 60 min metabolic inhibition (MI) and 5 min re‐energization (Rx). The effects of perfusion of HCO3− or HCO3−‐free buffer with or without the NHE inhibitor HOE642 (7 μM) were investigated during MI and Rx. In HCO3−‐free conditions, HOE642 reduced the percentage of cells developing rigor during MI from 79 ± 1% to 40 ± 4% (P < 0.001) without modifying the time at which rigor appeared. This resulted in a 30% reduction of hypercontracture during Rx (P < 0.01). The presence of HCO3− abolished the protective effect of HOE642 against rigor. Cells that had developed rigor underwent hypercontracture during Rx independently of treatment allocation. Ratiofluorescence measurement demonstrated that the rise in cytosolic Ca2+ (fura‐2) occurred only after the onset of rigor, and was not influenced by HOE642. NHE inhibition did not modify Na+ rise (SBFI) during MI, but exaggerated the initial fall of intracellular pH (BCEFC). In conclusion, HOE642 has a protective effect against rigor during energy deprivation, but only when HCO3−‐dependent transporters are inhibited. This effect is independent of changes in cytosolic Na+ or Ca2+ concentrations.

[1]  W. Schaper,et al.  Effects of a New Na+/H+ Antiporter Inhibitor on Postischemic Reperfusion in Pig Heart , 1994, Journal of cardiovascular pharmacology.

[2]  M. Tani,et al.  Role of Intracellular Na+ in Ca2+ Overload and Depressed Recovery of Ventricular Function of Reperfused Ischemic Rat Hearts Possible Involvement of H+-Na+ and Na+-Ca2+ Exchange , 1989, Circulation research.

[3]  R. Haworth,et al.  Contracture in Isolated Adult Rat Heart Cells: Role of Ca2+, ATP, and Compartmentation , 1981, Circulation research.

[4]  C. Schade-Brittinger,et al.  Time-dependent protection by Na+/H+ exchange inhibition in a regionally ischemic, reperfused porcine heart preparation with low residual blood flow. , 1998, Journal of molecular and cellular cardiology.

[5]  P. Cobbold,et al.  Cytosolic free Ca2+ in single rat heart cells during anoxia and reoxygenation. , 1987, The Biochemical journal.

[6]  R. London,et al.  Amiloride delays the ischemia-induced rise in cytosolic free calcium. , 1991, Circulation research.

[7]  T. Ruigrok,et al.  The role of the Na+ channel in the accumulation of intracellular Na+ during myocardial ischemia: consequences for post-ischemic recovery. , 1997, Journal of molecular and cellular cardiology.

[8]  B. Siegmund,et al.  Sarcolemmal integrity and metabolic competence of cardiomyocytes under anoxia-reoxygenation. , 1990, The American journal of physiology.

[9]  H. Hayashi,et al.  Na+/H+ and Na+/Ca2+ exchange in regulation of [Na+]i and [Ca2+]i during metabolic inhibition. , 1995, The American journal of physiology.

[10]  R. Ramasamy,et al.  Effect of lidocaine on contracture, intracellular sodium, and pH in ischemic rat hearts. , 1993, The American journal of physiology.

[11]  T. Ruigrok,et al.  Both Na+-K+ ATPase and Na +-H+ exchanger are immediately active upon post-ischemic reperfusion in isolated rat hearts. , 1998, Journal of molecular and cellular cardiology.

[12]  J. Soler‐Soler,et al.  Pre-treatment with trimetazidine increases sarcolemmal mechanical resistance in reoxygenated myocytes. , 1996, Cardiovascular research.

[13]  J. Soler‐Soler,et al.  Prevention of ischemic rigor contracture during coronary occlusion by inhibition of Na(+)-H+ exchange. , 1997, Cardiovascular research.

[14]  W. Cascio,et al.  Hypercapnic acidosis and dimethyl amiloride reduce reperfusion induced cell death in ischaemic ventricular myocardium. , 1995, Cardiovascular research.

[15]  E. Lakatta,et al.  Direct Observation of the “Oxygen Paradox” in Single Rat Ventricular Myocytes , 1985, Circulation research.

[16]  G. Elzinga,et al.  Rigor and contracture: the role of phosphorus compounds and cytosolic Ca2+ , 1990 .

[17]  J. Inserte,et al.  The role of Na+-H+ exchange occurring during hypoxia in the genesis of reoxygenation-induced myocardial oedema. , 1997, Journal of molecular and cellular cardiology.

[18]  G. Pohost,et al.  NMR measurements of Na+ and cellular energy in ischemic rat heart: role of Na(+)-H+ exchange. , 1993, The American journal of physiology.

[19]  J. Soler‐Soler,et al.  Effect of osmotic stress on sarcolemmal integrity of isolated cardiomyocytes following transient metabolic inhibition. , 1995, Cardiovascular research.

[20]  D. Noble,et al.  Modelling myocardial ischaemia and reperfusion. , 1998, Progress in biophysics and molecular biology.

[21]  D. Durrer,et al.  Tissue Osmolality, Cell Swelling, and Reperfusion in Acute Regional Myocardial Ischemia in the Isolated Porcine Heart , 1981, Circulation research.

[22]  K. Ytrehus,et al.  Inhibition of sodium-hydrogen exchange reduces infarct size in the isolated rat heart--a protective additive to ischaemic preconditioning. , 1995, Cardiovascular research.

[23]  H. Piper,et al.  Protection of energy status of hypoxic cardiomyocytes by mild acidosis. , 1992, Journal of molecular and cellular cardiology.

[24]  S. Harrison,et al.  Changes in contraction, cytosolic Ca2+ and pH during metabolic inhibition and upon restoration of mitochondrial respiration in rat ventricular myocytes , 1998, Experimental physiology.

[25]  Y. Ladilov,et al.  Protection of reoxygenated cardiomyocytes against hypercontracture by inhibition of Na+/H+ exchange. , 1995, The American journal of physiology.

[26]  B. Herman,et al.  Protection by acidotic pH against anoxia/reoxygenation injury to rat neonatal cardiac myocytes. , 1991, Biochemical and biophysical research communications.

[27]  R. Vaughan-Jones,et al.  Characterization of intracellular pH regulation in the guinea‐pig ventricular myocyte , 1999, The Journal of physiology.