A major site for the damaging effects of chronic excessive ethanol (EtOH) consumption is the heart. Acutely, EtOH is negatively inotropic, in part, by interfering with excitation-contraction coupling, reducing the magnitude of electrically triggered Ca2+ transients. At low concentrations, EtOH inhibits myocardial contractions without detectable Ca2+ changes, suggesting that force transduction is a second target of its acute effects, whose mechanisms are unknown. This project is based upon the hypothesis that cardiodepressant effects of EtOH are the result of its direct effects on the contractile apparatus. To test this hypothesis, the following specific aims will be addressed using normal rat trabeculae.
Aim 1 : Determine the dose-response of EtOH on resting stiffness and the mechanics of electrically stimulated trabeculae (stiffness, T0 or peak isometric tension, work, and dT/dt). This will determine the range of EtOH] that alters cytoskeletal and cross-bridge mechanics.
Aim 2 : Determine the direct effects of EtOH on cross-bridge mechanics. Chemically skinned trabeculae will be studied, bypassing the normal excitation-contraction pathway, directly controlling the contractile apparatus environment. The effects of EtOH] on T0, the [Ca]-tension relation, maximum shortening velocity, work, and passive and active stiffness will be determined. This will determine the [EtOH] required to effect directly force transduction and work output by the cardiac contractile system and the mechanical parameter most sensitive to EtOH.
Aim 3 : Determine the step in the cross-bridge cycle (force producing transition, phosphate release, detachment rate) responsible for the EtOH-sensitive mechanical parameters from aim 2. Laser photolysis of caged-compounds will initiate or perturb contractions of skinned trabeculae while monitoring force and stiffness.
Aim 4 : Determine the effects of chronic ethanol exposure on myocardial mechanics. Studies identical to the previous aims will be performed on trabeculae from rats fed EtOH for 2 to 26 weeks and normal controls. These studies will characterize the changes in mechanics produced by chronic EtOH exposure, identify the site of action, test for changes in EtOH sensitivity, and detect adaptations. The proposed studies will provide a more complete understanding of the cellular and molecular mechanisms responsible for the depressant effects of ethanol on myocardial contractility.
