Poloxamer 188 reduces the contraction-induced force decline in lumbrical muscles from mdx mice

Abstract

Duchenne Muscular Dystrophy is a genetic disease caused by the lack of the protein dystrophin. Dystrophic muscles are highly susceptible to contraction-induced injury, and following contractile activity, have disrupted plasma membranes that allow leakage of calcium ions into muscle fibers. Because of the direct relationship between increased intracellular calcium concentration and muscle dysfunction, therapeutic outcomes may be achieved through the identification and restriction of calcium influx pathways. Our purpose was to determine the contribution of sarcolemmal lesions to the force deficits caused by contraction-induced injury in dystrophic skeletal muscles. Using isolated lumbrical muscles from dystrophic (mdx) mice, we demonstrate for the first time that poloxamer 188 (P188), a membrane-sealing poloxamer, is effective in reducing the force deficit in a whole mdx skeletal muscle. A reduction in force deficit was also observed in mdx muscles that were exposed to a calcium-free environment. These results, coupled with previous observations of calcium entry into mdx muscle fibers during a similar contraction protocol, support the interpretation that extracellular calcium enters through sarcolemmal lesions and contributes to the force deficit observed in mdx muscles. The results provide a basis for potential therapeutic strategies directed at membrane stabilization of dystrophin-deficient skeletal muscle fibers.

Figures

Fig. 1.

Lumbrical muscle from the third digit of the forepaw of a mouse. A: wild-type (WT) muscle is shown beside a 30-gauge hypodermic needle. B: hematoxylin and eosin-stained cross section of a WT lumbrical muscle. Muscles typically consist of 200–250 fibers and are ∼300 μm in diameter. C: mdx muscle. Dystrophic features include presence of central nuclei and mononuclear cell infiltration. All scale bars are 200 μm and B and C share the same scale.

Fig. 2.

Force production of WT and mdx lumbrical muscles. A: example records of isometric force production. For clarity, only records of the first (1) and last (20) isometric contractions are shown. B: force production of WT (n = 6) and mdx (n = 8) lumbrical muscles during a protocol of 20 isometric contractions in normal Tyrode solution. Break in x-axis denotes a 10-min rest period. A two-way ANOVA was performed to determine effects of dystrophin deficiency and contraction number on the force deficit. #Difference between WT and mdx muscles at matching time points (P < 0.05).

Fig. 3.

Force production of mdx and WT lumbrical muscles at the end of 20 isometric contractions. A one-way ANOVA was performed followed by two separate post hoc comparisons between groups. In the first comparison, all groups were compared against the untreated mdx group (power > 0.8). In the second, all groups were compared against the WT group (power > 0.8). * and #, Difference from WT and untreated mdx group, respectively (P < 0.05).