Proceedings of The Physiological Society

University of Oxford (2011) Proc Physiol Soc 23, C46

Oral Communications

CaMKII overexpression reverses the effects of electroporation-induced damage on skeletal muscle twitch parameters

W. Eilers1, R. T. Jaspers2, A. de Haan1,2, M. Flueck1

1. Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, Manchester, United Kingdom. 2. Research Institute MOVE, VU University, Amsterdam, Netherlands.

Calcium/calmodulin-dependent protein kinase II is expressed in human skeletal muscle and activated during exercise (1). However, its function in skeletal muscle is still unclear. It has been hypothesised to be involved in regulating muscle phenotype and calcium release from, and uptake into, the sarcoplasmic reticulum, which would likely have functional consequences. We therefore investigated the effects of in vivo CaMKII overexpression on muscle force parameters of both fast-twitch and slow-twitch muscle. Female 3 month-old Wistar rats (190-225g, n=8) were anesthetised with 2-4% isoflurane through inhalation. Plasmids encoding α/β-CaMKII and a reporter plasmid were injected I.M. into the right m. gastrocnemius medialis (GM) and m. soleus (SOL) (CaMKII), while contra-lateral muscles were injected with the reporter only (Control). Plasmid injections were followed by electroporation and rats were kept in cages for 7 days afterwards. Muscle force parameters were measured in situ while rats were anaesthetised with 12.5% urethane (1.2ml/100g, injected I.P.) and rested on a heated pad. GM and SOL were isolated from surrounding muscles and their tendons connected to force transducers. The sciatic nerve was stimulated at supra-maximal intensity using a protocol consisting of twitches and a tetanic contraction (100Hz). Force data were recorded at 1000Hz. Time to peak twitch force (TTP), twitch half-relaxation time (HRT), maximum twitch force (Ftw) and maximum tetanic force (Fmax) was calculated from data obtained at optimum muscle length. The same contraction parameters were determined for a group of non-transfected muscles (NT; n=8). Data (absolute means ± S.E.M. are shown) were normalised to mean NT values. Effects of CaMKII overexpression (Control vs. CaMKII) and the electroporation procedure itself (NT vs. Control) were analysed with separate factorial ANOVA’s followed by paired and independent t-tests, respectively, for each muscle. Only intra-animal muscle pairs were used to determine the effects of CaMKII overexpression. Overall, electroporation increased TTP (p=.01), HRT (p=.01) and decreased Fmax (p≤.01). This was associated with the presence of centrally nucleated fibres in the electroporated region. CaMKII overexpression decreased TTP (p=.01) and HRT (p=.02), but did not increase Fmax significantly (p=.26). Ftw was not significantly affected by electroporation or CaMKII overexpression. Changes (Control vs. CaMKII) in SOL and GM followed similar trends (SOL: TTP (ms), 134±5 vs. 111±6, p=.05; HRT (ms), 176±6 vs. 145±8, p=.02. GM: TTP (ms), 52±3 vs. 46±2, p=.10; HRT (ms), 56±5 vs. 50±4, p=.27). We conclude that CaMKII overexpression mitigated or reversed the effects of electroporation-related damage on twitch characteristics. It remains to be determined whether this is due to acute effects or the result of structural adaptations.

Where applicable, experiments conform with Society ethical requirements