RT Journal Article
SR Electronic
T1 Mechanisms for the Paradoxical Resistance to d-Tubocurarine during Immobilization-Induced Muscle Atrophy
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 443
OP 451
VO 283
IS 2
A1 Chikwendu Ibebunjo
A1 Michael T. Nosek
A1 Mohammed S. Itani
A1 Jeevendra A. J. Martyn
YR 1997
UL http://jpet.aspetjournals.org/content/283/2/443.abstract
AB This study investigated whether immobilization-induced hyposensitivity to d-tubocurarine (dTC), up-regulation of acetylcholine receptors (AChRs) and changes in fiber size and motor endplate size persist indefinitely and whether they are causally related. Unilateral disuse of the tibialis muscle was produced in adult rats by pinning the knee and ankle joints at 90° flexion. The contralateral unpinned and a separate group of sham-pinned legs served as controls. After 7, 14 or 28 days of disuse, the in vivo dose of dTC that produced 50% depression of nerve-evoked twitch (ED50) in the tibialis muscle increased 3.0-, 3.2- and 2.1-fold (P < .05), and membrane AChRs increased 6.0- (P < .05), 6.3- (P > .05) and 1.2-fold (P > .395) relative to control, respectively. Disuse caused muscle fiber atrophy (P < .01) but did not affect endplate size. Hence, the ratio of endplate size to fiber size increased. There was a transient increase in gene expression of all (including de novo expression of the γ) subunits of the AChR, peaking at day 7 and returning to normal by day 28 of immobilization. The ED50 of dTC correlated directly with AChRs (R2= 0.51; P < .0001) or the ratio of endplate size to fiber size (R2 = 0.30; P < .001), and inversely with fiber size (R2 = 0.43, P < .0001). It is proposed that acting together, but not singly, the changes in AChRs, fiber size and relative endplate size contribute to the magnitude and time course of the resistance to dTC produced by chronic disuse. The American Society for Pharmacology and Experimental Therapeutics