CALCIUM DYNAMICS IN CARDIAC MYOCYTES AS A TARGET OF DICHLOROMETHANE CARDIOTOXICITY

The purpose of the present study was to determine if cardiac actions o f dichloromethane (DCM) in vivo correlate with in vitro alterations of Ca2+ dynamics in cardiac myocytes. Neonatal rat ventricular myocytes were obtained from 2- to 4-day-old rats, and electrically induced fluc tuations of cytosolic free Ca2+ concentration ([Ca2+](i)) in single ca rdiomyocytes were investigated using spectrofluorometric analysis of f ura-2-[Ca2+](i) binding. In cultured myocytes, cumulative exposure to 0.64-40.96 mM DCM resulted in a concentration-dependent and reversible decrease in the magnitude of [Ca2+](i) transients with IC10 and IC50 values of 7.98 and 18.82 mM, respectively. Total inhibition of [Ca2+]( i) transients and cessation of beating were observed at 40.96 mM DCM. Suffusion with DCM for 40 min did not cause morphological alterations of the myocytes. In a urethane-anesthetized rat model, left ventricula r pressure was measured by introducing a tip catheter via the carotid artery into the left ventricle, the ECG was recorded by two needle ele ctrodes applied subcutaneously to the chest wall, and arterial pressur e was measured via the femoral artery. Oral administration of 3.1-12.4 mmol DCM/kg resulted in DCM blood concentrations between 1.0 and 1.6 m M, accompanied by a dose-dependent decrease in contractile force and h eart rate without influencing blood pressure and ECG tracings. Moreove r, DCM treatment provided significant protection against arrhythmia de velopment due to CaCl2-infusion. In spite of the slight discrepancy be tween DCM blood concentrations and in vitro concentrations of DCM for [Ca2+](i) transient inhibition, present data are consistent with the v iew that cardiac effects after DCM exposure are mediated by alteration s of Ca2+ dynamics during excitation-contraction coupling.