CREATINE SUPPLEMENTATION IMPROVES SARCOPLASMIC RETICULUM FUNCTION IN DYSTROPHIC SKELETAL MUSCLE

Emma Rybalka, Michael F. Carey, Alan Hayes, Exercise Metabolism Unit; Centre for Rehabilitation, Exercise and Sport Science, Victoria University, Victoria.

Since the progressive degeneration characteristic of dystrophic disease is governed by the Ca²⁺-induced damage cycle, improving the Ca²⁺ handling capacity of dystrophin-deficient muscle could be of potential therapeutic benefit. Pulido et al.¹ have shown increased survival of dystrophic mdx myotubes following creatine pre-treatment that was associated with decreased intracellular Ca²⁺ concentrations. This was attributed to improved sarcoplasmic reticulum (SR) Ca²⁺ ATPase function, although this was not measured. Thus, we have investigated SR Ca²⁺ uptake activity in mdx skeletal muscle following dietary creatine supplementation.

Female mdx mice were randomly separated into non-supplemented (n=8) and creatine-supplemented (n=8) groups. A third group of normal mice (C57BL/10ScCn) was used for comparisons between normal and dystrophic animals (n=8). Creatine was administered reconstituted in normal chow over a 6-week period. On the day of experimentation, animals were anaethetised with sodium pentobarbitone (60 mg/kg body weight; i.p.) and the tibialis anterior (TA) and diaphragm excised. SR Ca²⁺ uptake rate was measured spectrofluorometrically in homogenized vesicle preparations using the Ca²⁺-specific fluorophore Fura-2.

SR Ca²⁺ uptake rate was significantly faster in unsupplemented dystrophic muscle (P<0.05) compared to normal muscles, and notably faster in diaphragm than TA (P<0.01). SR Ca²⁺ uptake rate was further increased after creatine treatment in both TA and diaphragm (P<0.01) compared with unsupplemented muscle, and again faster in diaphragm compared with TA (P<0.05).

These results indicate that ATP-supported SR Ca²⁺ uptake is already up-regulated in dystrophic muscle, most likely in response to the high intracellular Ca²⁺ environment. Dietary creatine supplementation further improved SR Ca²⁺ uptake activity by increasing ATP availability to the Ca²⁺-ATPase pump, and could thus potentially be used as a therapeutic adjunct for the treatment of muscular dystrophy.

(1) Pulido SM, Passaquin AC, Leijendekker WJ, Challet C, Wallimann T, Ruegg UT. FEBS. 1998;439:357-362.