Abstract

The purpose of this study was to determine whether 4-chloro-m-cresol (4-CmC) could generate caffeine-like responses in ferret cardiac muscle. The concentration dependence of 4-CmC-mediated release of Ca²⁺ from the sarcoplasmic reticulum was studied in intact cardiac trabeculae and saponin-skinned fibers in which the sarcoplasmic reticulum was loaded with Ca²⁺. In intact and saponin-skinned preparations isolated from right ventricle, the effect of 4-CmC on sarcoplasmic reticulum Ca²⁺ content was estimated by analysis of caffeine contracture after application of chlorocresol. In addition, the effects of 4-CmC on maximal Ca²⁺-activated tension and the Ca²⁺ sensitivity of myofibrils were analyzed by using Triton-skinned cardiac fibers. The results show that 4-CmC generates a contractile response in saponin-skinned but not intact fibers. The sarcoplasmic reticulum is implicated in the 4-CmC response; more precisely, in Ca²⁺ release via the ryanodine receptor. Moreover, 4-CmC, like caffeine, has effects on maximal Ca²⁺-activated tension and the Ca²⁺ sensitivity of myofibrils.