ETHANOL ACUTELY AND REVERSIBLY SUPPRESSES EXCITATION CONTRACTION COUPLING IN CARDIAC MYOCYTES

We used adult rat cardiac myocytes to examine the acute effects of 0.1-5.0% (vol/vol) ethanol (ETOH) on 1) the cytosolic [Ca2+] (Ca(i)) transient measured as the change in indo 1 fluorescence at 410/490 nm and contraction elicited by electrical stimulation of single cells and 2) the sarcoplasmic reticulum (SR) Ca2+ content in cell suspensions. During stimulation at 1 Hz, clinically relevant ETOH correlations (0.1-0.15% [vol/vol]) caused a 10-15% decrease in the contraction amplitude, measured by myocyte edge tracking, without decreasing the Ca(i) transient that initiates contraction. At higher ETOH concentrations (1-5% [vol/vol]), ETOH caused profound contractile depression and also reduced the magnitude of the Ca(i) transient. These effects were reversed within minutes of ETOH washout. Addition of norepinephrine (10-mu-M) to the bathing solution or an increase in bathing [Ca2+] in the continued presence of ETOH could also reverse its effects. The relation of the amplitude of the Ca(i) transient to the contraction amplitude measured across a range of bathing [Ca2+] was shifted by ETOH, such that for a given Ca(i) transient a marked reduction in contraction amplitude occurred. In unstimulated myocyte suspensions, ETOH (1-5% [vol/vol]) caused a concentration-dependent depletion of SR Ca2+ content, manifested as a diminution in the Ca(i) increase elicited by caffeine in the presence of extracellular EGTA and no added Ca2+. Thus, in rat cardiac myocytes a reduction in the myofilament Ca2+ response, possibly due to a decrease in myofilament Ca2+ sensitivity, is a mechanism for contractile depression due to clinically relevant ETOH concentrations. Higher concentrations of ETOH cause further contractile depression, in part, by inducing SR Ca2+ release and depleting the SR of Ca2+, leading to an attenuation of the Ca(i) transient elicited by electrical stimulation, and by further depressing the myofilament length-Ca2+ relation.