BACKGROUND AND AIMS: Motor unit (MU) force is regulated by neural and muscular mechanisms. Recently, effects of carnosine on skeletal muscle contractility have been broadly studied. We found that increased muscle carnosine content by beta-alanine supplementation improved MU contractility. Several studies showed that histidine-free diet decreases carnosine content and causes weight loss, anaemia or hypoproteinaemia but its effect on muscle contractility is unknown. Here we studied MU contractile properties in histidine-deprived rats with reduced muscle carnosine content. METHODS: Ten 6 mo male Wistar rats were randomly assigned to experimental (HFD) or control (CON) group fed histidine-free or standard diet for 14 days, respectively. In order to maintain the same level of body mass loss food intake was controlled and balanced between both groups. Body mass decreased by 11.7 and 10.6% in HFD and CON groups, respectively. RESULTS: In HFD group carnosine levels were lower than in CON group in white and red portion of MG muscle by 26% and 34%, respectively. Histidine deprivation did not result in lower muscle mass or muscle-to-body mass ratio. In electrophysiological experiments contractions of MUs in medial gastrocnemius (MG) muscle were evoked by electrical stimulation of ventral root filaments. MUs were classified into fast fatigable (FF), fast resistant (FR) and slow (S). Maximum tetanic force (TetF) and force profile during the two separate fatigue tests were analysed. The TetF did not differ between groups either in fast or slow MUs. During the first fatigue test in FR MU force was initially higher but from 40 to 120 s it was lower in HFD animals. Unexpectedly, in the second fatigue test the force of FR and S MU was better maintained in HFD than CON rats. CONCLUSIONS: The results indicate that short-term histidine deprivation and the carnosine decrease do not attenuate force of MUs. Moreover, compensatory mechanisms may be involved in the regulation of MU force in this condition. Support: grant 2013/09/B/NZ7/02554.
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