Fast and slow skeletal muscles: effect of ethanol on contractility of muscles from mice

We examined in vitro the effect of ethanol at four concentrations (0g%, 0.1g%, 0.2g%, and 0.4g%) on contractile parameters of 40 fast extensor digitorum longus (EDL) and 40 slow soleus muscles from healthy mice at 35C. Preparations were curarized to avoid the possible effect of ethanol on the terminal axons or skeletal neuromuscular junction. Contractile parameters measured included: (1) twitch and tetanic tension; (2) rate of tension development; (3) time to peak tension and half relaxation for twitch; (4) time to first evidence of relaxation in the tetanus; and (5) maximum rate of relaxation. The three lower concentrations of ethanol had no significant effect on muscle contractility; however, the 0.4g% dose reduced EDL twitch tension by 9%. High doses of ethanol (2.5g%) reduced the tetanic tension produced by the EDL and soleus muscles 31% and 26%, respectively. Ethanol at 2.5g% also reduced the twitch tension of the EDL and soleus by 50% and 38%, respectively. The data suggested that the 0.4g% is the highest dose of ethanol that should be used to dilute drugs in a solution that will bathe directly stimulated curarized muscle without confounding effects. In addition, it is highly unlikely that a direct effect of ethanol on muscle contractility in humans is related to an impairment in driving.