ABSTRACT
BACKGROUND: Three isoforms of the neuronal acetylcholine receptors (AChRs) have been described in muscle epsilonAChRs, gammaAChRs and alpha7AChRs. The adult neuromuscular junctions are composed of epsilonAChRs. During immobilization, new AChRs with subunit compositions of gammaAChRs and alpha7AChRs appear in the perijunctional and extrajunctional area. This study evaluated the contribution of these isoforms to neurotransmission during immobilization, by using waglerin-1 which selectively blocks the epsilonAChRs. METHODS: Male mice (n = 20) were used and each group was divided into sham operated or immobilized. A leg was immobilized in mice for 14 days by pinning, after which nerve-evoked twitch tension was examined under anesthesia in tibialis muscle of both legs, with the contralateral leg serving as control. Neuromuscular transmission was monitored by using a peripheral nerve stimulator with the tibialis muscle and sciatic nerve. Electrical stimuli of 0.2 msec duration were applied to sciatic nerve 2 Hz for 2 sec every 30 sec. After administration of waglerin-1, the evoked twitch was recorded. The percent depression of T1 relative to baseline was transformed to probit scale to determine the effective dose of waglerin-1 for 5%, 50%, and 95% twitch depression. RESULTS: The twitch tension in the control group was higher than immobilized group, confirming the efficacy of immobilization. Waglerin-1 produced 99% twitch suppression on the control group. But on the immobilized group, waglerin-1 produced only 70% twitch suppression even at 37 pg. CONCLUSIONS: The functional role of epsilonAChRs in neurotransmission decreases during immobilization while that of gammaAChRs and alpha7AChRs increases.