Effects of oxidation and reduction on contractile function in skeletal muscle fibres of the rat

• Published in: The Journal of physiology 2003-01, Vol.546 (1), p.149-163
• Main Authors: Lamb, G. D., Posterino, G. S.
• Format: Article
• Language: English
• Subjects: 2,2'-Dipyridyl - analogs & derivatives; 2,2'-Dipyridyl - pharmacology; Animals; Disulfides - pharmacology; Dithiothreitol - pharmacology; Glutathione - pharmacology; Hydrogen Peroxide - pharmacology; Muscle Contraction - drug effects; Muscle Contraction - physiology; Muscle Fibers, Skeletal - physiology; Muscle, Skeletal - drug effects; Muscle, Skeletal - physiology; Original; Oxidants - pharmacology; Oxidation-Reduction; Rats; Rats, Long-Evans; Sulfhydryl Reagents - pharmacology; Time Factors
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2002.027896

This study investigated the effects of the oxidants hydrogen peroxide (H 2 O 2 ) and 2,2′-dithiodipyridine (DTDP), and reductants, glutathione (GSH) and dithiothreitol (DTT), on the properties of the contractile apparatus of rat fast- and slow-twitch skeletal muscle fibres, in order to assess how oxidation affects muscle function. Skinned muscle fibres were activated in heavily-buffered Ca 2+ solutions. The force-[Ca 2+ ] relationship before and after various treatments was fitted by a Hill curve described by the maximum Ca 2+ -activated force, pCa 50 (-log 10 [Ca 2+ ] giving half-maximum force) and n H (the Hill coefficient). Exposing freshly skinned fibres to strong reducing conditions (i.e. 10 m m DTT or 5 m m GSH) had little if any effect on Ca 2+ sensitivity (pCa 50 or n H ). The effect of oxidants H 2 O 2 and DTDP depended on whether the fibre was relaxed (in pCa > 9) or activated during the exposure. In both fast- and slow-twitch fibres a 5 min exposure to 10 m m H 2 O 2 at pCa > 9 had no effect on pCa 50 , causing only a reduction in n H . In contrast, when fast-twitch fibres were activated in the presence of 10 m m H 2 O 2 (or 100 μ m DTDP) there was a substantial increase in pCa 50 (by ≈0.06 and 0.1, respectively), as well as larger decreases in n H than occurred in relaxed fibres, with all effects being reversed by DTT (10 m m , 10 min). In slow-twitch soleus fibres, the activation-dependent effect of DTDP was even greater (pCa 50 increased by ≈0.35), and it was found that the rate of reversal in DTT was also increased by activation. A separate important phenomenon was that fast-twitch fibres that had been oxidised with H 2 O 2 or DTDP (while either relaxed or activated) showed a paradoxical increase in Ca 2+ sensitivity (≈0.04 and 0.25 increase in pCa 50 , respectively) when briefly exposed to the endogenous reductant GSH (5 m m , 2 min). This effect was reversed by DTT or longer (> 20 min) exposure to GSH, did not occur in slow-twitch soleus fibres, and may contribute to post-tetanic potentiation in fast-twitch muscle. Maximum force was not affected by any of the above treatments, whereas exposure to a high concentration of DTDP (1 m m ) did greatly reduce force production. These findings reveal a number of novel and probably important effects of oxidation on the contractile apparatus in skeletal muscle fibres.