Doxorubicin-induced calcium release from cardiac sarcoplasmic reticulum vesicles

Abstract

Doxorubicin, an anthracycline glycoside antibiotic which has been widely used for treatment of several types of cancer (Goormaghtigh and Ruysschaer, 1984), displays a clinically important cardiac toxicity (Young et al., 1981) that can be dissociated from the antitumor activity. Although the main sites of toxicity have been postulated to be on the muscle membranes (Goormaghtigh and Ruysschaer, 1984; Harris and Doroshow, 1985), no information is available for a direct doxorubicin effect on the Ca 2+ fluxes in cardiac sarcoplasmic reticulum (SR). Previous studies have shown that micromolar doxorubicin triggers Ca 2+ release from skeletal SR vesicles (Zorzato et al., 1985). The objective of this study was to examine the effect of doxorubicin or caffeine on Ca 2+ fluxes in cardiac SR in the presence of various Ca 2+ release inhibitors. Addition of either doxorubicin (C 1/2 = 5 μ m), or caffeine (C 1/2 = 0.8 m m) triggered Ca 2+ release from canine cardiac SR loaded with 45Ca 2+ in the presence of 2 m m ATP. The maximal amount of Ca 2+ release triggered by doxorubicin (38% of the total loaded Ca 2+) was significantly higher than that released by caffeine (25%). Plots of the amount of Ca 2+ release triggered by 20 μ m doxorubicin or 2 m m caffeine vs. free Ca 2+ concentration were a bell-shaped, with maximal Ca 2+ release at 0.2 μ m Ca 2+. Ca 2+ release triggered by either 20 μ m doxorubicin or 2 m m caffeine was inhibited by ruthenium red (0.1 to 2 μ m), ryanodine (1 to 100 μ m) or tetracaine (0·1 to 1 m m), whereas 2 m m caffeine did not further activate Ca 2+ release triggered by 50 μ m doxorubicin, suggesting that the drugs may share the same Ca 2+ release channel.