l ‐arginine ingestion inhibits eccentric contraction‐induced proteolysis and force deficit via S ‐nitrosylation of calpain

It has been shown that calpains are involved in the proteolysis of muscle proteins that occurs with eccentric contraction ( ECC ) and that exogenously applied nitric oxide decreases the calpain‐mediated proteolysis. The aim of this study was to examine the effects of ingestion of l ‐arginine ( ARG ), a nitric oxide precursor, on ECC ‐related calpain activation. In the first and second experiments, male Wistar rats were given ARG in water for 7 days starting from 3 days before the ECC protocol (average ingestion, ~600 mg kg‐body wt −1  day −1 ). Tibialis anterior muscles underwent 200 repeated ECC s and, subsequently, were excised 3 days later. Whole muscle analyses (the first experiment) revealed that ARG attenuated ECC ‐induced force deficit and autolysis of calpain‐1, and increased the amounts of S ‐nitrosylated calpain‐1. Regarding ryanodine receptor (RyR) and dihydropyridine receptor ( DHPR ), ECC ‐induced proteolysis was completely inhibited by ARG , whereas the inhibition was partial for junctophilin‐1 ( JP 1). Skinned fiber analyses (the second experiment) showed that ARG also inhibited ECC ‐elicited reductions in the ratio of depolarization‐induced to maximum Ca 2+ ‐activated force. In the third experiment, homogenates of rested muscles were treated with S ‐nitrosylating agent, S ‐nitrosoglutathione ( GSNO ), and/or high Ca 2+ concentration ([Ca 2+ ]). Treatment with high [Ca 2+ ] and without GSNO produced proteolysis of RyR, DHPR , and JP 1. On the other hand, treatment with high [Ca 2+ ] and GSNO caused complete inhibition of RyR and DHPR proteolysis and partial inhibition of JP 1 proteolysis. These results indicate that ARG ingestion can attenuate ECC ‐induced proteolysis of Ca 2+ regulatory proteins and force deficit by decreasing calpain activation via S ‐nitrosylation.