Disruption by Hypochlorous Acid and Restoration by Dithiothreitol

Hypochlorous acid (HOCI) is a toxic oxidant produced by neutrophils at sites of cardiac inflammation. To examine the effect of this oxidant on Ca2 ' homeostasis in the heart, isolated rabbit ventricular myocytes were iontophoretically loaded with the Ca2 ' indicator fura 2 and superfused with 100 puM HOCI under voltage-clamp conditions. Ca24 transients and the corresponding Ca24 currents were elicited by 300-msec depolarizing pulses from-40 to 0 mV. Within 200 seconds after HOCI addition, the amplitude of the Ca2+ transients was reduced from 402±89 to 82+29 nM (p<0.01) while intracellular free Ca24 concentration ([Ca2+1]) increased from 78±+16 to 265+±48 nM (p<0.01). During this time, the amplitude of the slow inward currents increased by 10%, while steady-state holding current remained stable. This sustained steady-state rise in [Ca21]1 occurred even in the absence of extracellular Ca2+ but was virtually abolished by a 20-second preexposure to 10 mM caffeine, suggesting that the major source of this Ca2+ was the sarcoplasmic reticulum. Although washout ofHOCI failed to induce recovery, subsequent exposure to the dithiol reducing agent dithiothreitol caused a rapid restoration of both the steady-state [Ca2+1i and Ca2+ transient amplitude. We conclude that 1) HOCI caused a rise of [Ca211 by inducing the release of Ca24 from internal stores and impairing cellula