Aim:To investigate the effect of magnesium sulfate and its interaction with the non-depolarizing muscle relaxant vecuronium at adult muscle-type acetylcholine receptors in vitro. Methods: Adult muscle-type acetylcholine receptors were expressed in HEK293 cells. Drug-containing solution was applied via a gravity-driven perfusion system. The inward currents were activated by brief application of acetylcholine (ACh), and recorded using whole-cell voltage-clamp technique. Results: Magnesium sulfate (1-100 mmol/L) inhibited the inward currents induced ACh (10 μmol/L) in a concentration-dependent manner (IC 50 =29.2 mmol/L). The inhibition of magnesium sulfate was non-competitive. In contrast, vecuronium produced a potent inhibition on the adult muscle-type acetylcholine receptor (IC 50 =8.7 nmol/L) by competitive antagonism. Magnesium sulfate at the concentrations of 1, 3, and 6 mmol/L markedly enhanced the inhibition of vecuronium (10 nmol/L) on adult muscle-type acetylcholine receptors. Conclusion: Clinical enhancement of vecuronium-induced muscle relaxation by magnesium sulfate can be attributed partly to synergism between magnesium sulfate and non-depolarizing muscle relaxants at adult muscle-type acetylcholine receptors.

Background:Rocuronium is an alternative to succinylcholine for rapid tracheal intubation after major thermal injury and other forms of critical illness that cause denervation changes in skeletal muscle. Rocuronium may decrease the potencies of non-depolarizing muscle relaxants. Objectives: Examine whether potency of rocuronium changed during the first month after denervation, and investigate the effects of skeletal muscle denervation on potency of rocuronium. Methods: The denervation mouse model was developed to create denervated individual cells from the flexor digitorum brevis of the hindfoot. The skeletal muscle cells were examined at day 0 in the innervated control and days 1, 4, 7, 14, 21, and 28 in the denervation group. Nicotinic acetylcholine receptors in the cells were activated with 30 M acetylcholine, alone or in combination with various concentrations of rocuronium. Currents were recorded with a whole-cell patch-clamp technique. Results: Rocuronium reversibly inhibited acetylcholine-activated currents in a dose-dependent fashion at different times after denervation. The inhibition concentration for the half-maximal responses of rocuronium increased 1.2-(p >0.05), 1.8-, 2.8-, 2.3-, 2.1-, and 1.9-fold (p <0.01) at day 1, 4, 7, 14, 21, and 28 after denervation, respectively, compared to that at day 0 after denervation. Conclusion: Rocuronium dose required to achieve satisfactory clinical effects changed at different durations after skeletal muscle denervation.