Impairment of cardiac contractility and sarcoplasmic reticulum Ca2+ ATPase activity by hypochlorous acid: reversal by dithiothreitol

Abstract

Isolated rat hearts perfused with 100 μM hypochlorous acid (HOCl), a powerful oxidant produced by activated neutrophils, exhibited progressive impairment of contractile performance suggestive of a cytosolic Ca2+ overload (increased left ventricular end-diastolic pressure, increased aortic root perfusion pressure, and depressed pulse pressure). Sarcoplasmic reticulum (SR) enriched microsomal preparations isolated from HOCl-perfused hearts showed a significant decline, when compared with control hearts, in both Ca2+ ATPase activity (123 ± 40 vs. 473 ± 46 nmol Pi∙mg−1 protein∙min−1) and Ca2+ uptake (12 ± 5 vs. 46 ± 4 nmol Ca2+∙mg−1 protein∙min−1). The sulfhydryl content in Ca2+ ATPase and other proteins, as determined by [14C]iodoacetamide binding, was also progressively depleted in HOCl-perfused hearts. Perfusion of the HOCl-treated hearts with dithiothreitol (DTT), a disulfide reducing agent, resulted in a time-dependent attenuation, and eventual partial reversal, of the dysfunction in both contractility and SR Ca2+ ATPase activity. Protein thiol levels were concomitantly restored to near control values. The data indicate that HOCl-induced contractile dysfunction in heart is related to the inactivation of the SR Ca2+ ATPase as a result of thiol oxidation and suggest that DTT is capable of reversing this dysfunction in situ by reducing the oxidized sulfhydryls in the Ca2+ ATPase.Key words: hypochlorous acid, dithiothreitol, cardiac sarcoplasmic reticulum, Ca2+ ATPase, protein sulfhydryl.