Anthracycline-induced Tension in Permeabilized Cardiac Fibers: Evidence for the Activation of the Calcium Release Channel of Sarcoplasmic Reticulum

Anthracyclines, such as doxorubicin (DOX), are important cancer chemotherapeutic agents that are cardiotoxic. The mechanism for the cardiotoxicity is not well-defined. Recent studies have concluded that anthracyclines release calcium (Ca2+) from membrane fractions containing sarcoplasmic reticulum (SR). To determine whether anthracyclines release Ca2+in situ from cardiac SR, the effects of DOX on Ca2+-activated contractions were analyzed in membrane-permeabilized and membrane-intact fibers from rabbit heart. DOX (10-120 μM) induced tension development in calcium-preloaded permeabilized fibers. DOX-induced tension required submicromolar Ca2+, and was blocked by ruthenium red (20 μM) and Triton X-100 treatment, characteristics shared by caffeine-induced tension referable to SR Ca2+-release. DOX (50 μM) did not alter the maximum Ca2+-activated tension or shift the Ca2+ concentration-tension relationship of permeabilized fibers, indicating no effects of DOX on the myofilaments. DOX (44-350 μM) depressed post-rest isometric contractility of membrane-intact fibers but did not inhibit steady-state contractility (at 1 Hz; 2.5 Mm Ca2+), similar to effects of caffeine and submicromolar ryanodine. The specific effects of DOX on post-rest contractility of membrane-intact fibers are consistent with DOX-induced Ca2+ release from the SR of membrane-permeabilized fibers. Thus, DOX alters SR Ca2+ release in situ which may contribute to the inotropic and lusitropic dysfunction observed with anthracyclines