Aim: to investigate the changing resistance to nondepolarizing muscle relaxants (NDMRs) during the first month after denervation.
Methods: the denervated and innervated skeletal muscle cells were examined on days 1, 4, 7, 14, 21, and 28 after denervation. Individual denervated and innervated cells were prepared from the flexor digitorum brevis of the surgically denervated and contralateral hind feet, respectively. Nicotinic acetylcholine receptors (nAChRs) in the cells were activated with 30 micromol/L acetylcholine, either alone or in combination with various concentrations of vecuronium. Currents were recorded using a whole-cell patch-clamp technique.
Results: the concentrations of vecuronium resulting in half-maximal inhibitory responses (IC(50)) increased 1.2- (P>0.05), 1.7-, 3.7-, 2.5-, 1.9-, and 1.8-fold (P<0.05) at Days 1, 4, 7, 14, 21, and 28 after denervation, respectively, compared to the innervated control. Resistance to vecuronium appeared at Day 4, peaked at Day 7, and declined at Day 14 after denervation. Nevertheless, IC(50) values at Day 28 remained significantly higher than those for the innervated control, suggesting that the resistance to vecuronium had not disappeared at Day 28.
Conclusion: The NDMR doses required to achieve satisfactory clinical effects differ at different times after muscle denervation.