Hypochlorous Acid Mobilizes Intracellular Zinc in Isolated Rat Heart Myocytes

Neutrophil oxidants appear to cause contractile dysfunction in reperfused ischemic myocardium. This "reperfusion injury" may result from the intracellular mobilization of various metals. We examined the ability of hypochlorous acid (HOCl), a highly reactive neutrophil oxidant, to mobilize cellular zinc in cardiac tissue. To monitor cellular zinc concentrations, isolated rat heart myocytes were loaded with N-(6-methoxy-8-quinolyl)-p-toluenesulfonamide (TSQ), a zinc-specific fluorescent chelator. Superfusion of the TSQ-loaded cells with HOCl (50 μM) resulted in a two-fold increase in cellular fluorescence within 15 min, indicating an increase in free Zn2+ concentration. Superfusion of the HOCl-treated cells with ethylene glycol bis (β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA), a non membrane-permeant zinc chelator, did not decrease cellular fluorescence. However, superfusion with N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), or dithiothreitol (DTT), two membrane-permeant heavy metal chelators, rapidly diminished fluorescence, suggesting that the increase in TSQ fluorescence was caused by an intracellular increase in free Zn2+. The myocytes retained their rod-shaped morphology throughout these procedures. These data show, for the first time, that HOCl can mobilize intracellular zinc in viable cardiac myocytes. In view of the important intracellular role played by zinc, the mobilization of this metal by oxidants may contribute to the functional alterations observed in reperfused myocardium. Moreover, the ability of TPEN and DTT to complex the HOCl-mobilized zinc suggests that these chelators may be capable of attenuating or reversing these effects.