Inhibition of stretch-activated channels during eccentric muscle contraction attenuates p70(S6K) activation

Eccentric contractions (EC) are known to result in muscle hypertrophy, potentially through activation of the Akt-mammalian target of rapamycin-p70 S6 kinase (p70(S6K)) signaling pathway. Previous work has also demonstrated that EC result in the opening of stretch-activated channels (SAC), and inhibition of these channels resulted in an attenuation of EC-induced muscle hypertrophy. The purpose of this study was to test the hypothesis that a known intracellular pathway directly associated with muscle hypertrophy is coupled to the opening of SAC. Specifically, we measured the activation of the Akt, GSK-3 beta, p70S6K, and ribosomal protein S6 following a single bout of EC in the rat tibialis anterior (TA) muscle. The TA muscles performed four sets of six repetitions of EC. In vivo blockade of SAC was performed by a continuous oral treatment with streptomycin in the drinking water (4 g/1) or by intravenous infusion of 80 mu mol/kg gadolinium (Gd3+). EC increased the degree of Akt and p70(S6K) phosphorylation in the TA muscle, whereas in animals in which SAC had been inhibited, there was a reduced capacity for EC to induce Akt or p70(S6K) phosphorylation. Accompanying this reduced activation of Akt and p70(S6K) was a failure to phosphorylate GSK-3 beta or S6 when SAC were inhibited. The results from these data indicate the necessity of functional SAC for the complete activation of Akt and p70(S6K) pathway in response to EC.