Pharmacological Inhibition of Ryanodine Receptors Immediately after Eccentric Contractions Exercise Effectively Reduces Exercise-induced Muscle Damage in Rat Skeletal Muscle

Calcium ions (Ca2+) exert a pivotal role in cell signaling via modulation of spatial and temporal intracellular Ca2+ ([Ca2+]i) patterns to regulate multiple cellular functions. Eccentric contractions (ECC) induce Ca2+ influx from the extracellular space via Stretch Activated Channels (SACs) promoting intramyocyte Ca2+ accumulation and contributing to subsequent muscle damage. How specific Ca2+ dynamics patterns relate to muscle damage and the contribution of SACs versus ryanodine receptors (RyR) to [Ca2+]i following ECC is unknown. PURPOSE: We tested the hypothesis that, following ECC, 1) there is a specific spatial-temporal [Ca2+]i pattern mediated by intracellular mechanisms other than SACs (perhaps RyR), and 2) this [Ca2+]i pattern relates to the muscle damage process. METHODS: Tibialis anterior (TA) muscle of adult male Wistar Rats without ECC (CONT) and 5 (ECC5h) and 24 hours (ECC24h) post- ECC (5 sets of 40 contractions) were imaged in vivo for [Ca2+]i and subsequent in vitro histological assessment. The TA muscle was loaded with Ca2+ indicator Fura2-AM and the 340/380 nm ratio evaluated [Ca2+]i distribution during RyR (dantrolene, DAN) or SACs (gadolinium, Gd3+) inhibition. Muscle histology was assessed microscopically on hematoxylin-eosin stained sections. RESULTS: Compared to CONT, where [Ca2+]i distribution was fairly uniform, high intracellular [Ca2+]i area (Ratio > 1.39 i.e., > 1 SD of CONT mean) was increased in ECC5h (CONT, 14.0 ± 8.0; ECC5h: 52.0 ± 7.4%, p < 0.01). Superfusion with DAN decreased [Ca2+]i in a concentration-dependent manner (before DAN: 1.72 ± 0.07, DAN 50 μM: 1.52 ± 0.09, DAN 100 μM: 1.31 ± 0.13, p < 0.05 vs before), but Gd3+ did not (before Gd3+: 1.52 ± 0.02, Gd3+ 20 μM: 1.51 ± 0.02, Gd3+ 100 μM: 1.57 ± 0.13, all p > 0.05). DAN treatment by intraperitoneal injection also decreased high [Ca2+]i area (ECC5h + DAN: 6.4 ± 3.1%, p < 0.01) and the ECC-induced muscle damage (ECC24h, 63.2 ± 1.0%; ECC24h + DAN, 29.1 ± 2.2%, p < 0.01). CONCLUSION: Following ECC the characteristic pattern with increased [Ca2+]i heterogeneity and high [Ca2+]i area is mediated predominantly by RyR and relates closely to the magnitude of muscle damage. These findings suggest that ECC-induced muscle damage can be effectively reduced by pharmacological RyR suppression immediately after ECC exercise.