Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, C45
The effect of ethyl alcohol on contractions of isolated mammalian skeletal muscle fibres.
P. W. Robinson1, S. A. Aston1, M. E. Coupland1, K. W. Ranatunga1
1. School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom.
Muscle strength is reversibly decreased with acute and chronic alcohol ingestion (Urbano-Marquez et al. 1989). In vitro ethanol has been shown to decrease both isometric twitch and tetanic contractions in isolated rat diaphragm preparations and isolated frog muscle fibres (Khan 1981, Pagala et al. 1995). Current evidence suggests that this alcohol induced depression of force is via effects on cell membrane properties or by effects on Ca2+ channels in the sarcoplasmic reticulum. It is not known if there are any direct effects of alcohol on the actomyosin contractile process. Here we examine the effect of alcohol on contractions of isolated intact and skinned mammalian muscle fibres. Adult male Wistar rats (275-350g) were killed with an intraperitoneal injection of an overdose of Sodium Pentobarbitone (150mg kg-1). Intact fibre bundle preparations from rat flexor hallucis brevis muscle were prepared and mounted in a trough system between a motor and a force transducer (Coupland & Ranatunga 2003). Fibre bundles were bathed in physiological Ringer solutions with different ethanol concentrations (range 0.6% to 3%v/v). Twitch and tetanic tensions were recorded at 20°C. Chemically skinned fibres (using the detergent 0.5% Brij 58) were prepared from rabbit psoas muscle (killed by an intravenous overdose of Sodium Pentobarbitone (150mg Kg-1). Fibres were maximally Ca2+ activated by exposing them from a relaxing, to a pre-activating and then into an activating solution at 20°C (see Coupland et al. 2001) with different ethanol concentrations (range 0.5% to 3%v/v). Force transducer output was recorded using CED 1401 laboratory interface and Signal Averager software (Cambridge Design Ltd). Tension data was expressed as percentages of the control (mean ± SEM), compared by ANOVA, with Bonferroni’s multiple comparison test. There was no significant tension depression seen with 0.6% ethanol, but increasing ethanol concentrations depressed tension in a concentration dependent manner. In the intact fibre experiments 3% ethanol reversibly depressed the tetanic tension by 27.1±6.8% (p<0.01, n=5) and the twitch tension by 58.7±5.9% (p<0.001, n=5). In the skinned fibres maximal Ca2+-activated tension was significantly depressed by 17.5±4.9% (p<0.05, n=5) with 2% ethanol and 37.3±4.2% (p<0.001, n=5) with 3% ethanol. Preliminary experiments at 10°C and 30°C suggest that alcohol induced tension depression decreases with increase of temperature. Our results confirm previous findings that alcohol induces tension depression in active intact muscle; additionally, experiments on skinned fibres provide evidence that alcohol has a direct depressive effect on actomyosin (crossbridge) interaction.
Where applicable, experiments conform with Society ethical requirements