Ca(2+) permeation and/or binding to CaV1.1 fine-tunes skeletal muscle Ca(2+) signaling to sustain muscle function.

Chang Seok Lee, Adan Dagnino-Acosta, Viktor Yarotskyy, Amy Hanna, Alla Lyfenko, Mark Knoblauch, Dimitra K Georgiou, Ross A Poché, Michael W Swank, Cheng Long, Iskander I Ismailov, Johanna Lanner, Ted Tran, KeKe Dong, George G Rodney, Mary E Dickinson, Christine Beeton, Pumin Zhang, Robert T Dirksen, Susan L Hamilton

Index: Skelet. Muscle 5 , 4, (2015)

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Abstract

Ca(2+) influx through CaV1.1 is not required for skeletal muscle excitation-contraction coupling, but whether Ca(2+) permeation through CaV1.1 during sustained muscle activity plays a functional role in mammalian skeletal muscle has not been assessed.We generated a mouse with a Ca(2+) binding and/or permeation defect in the voltage-dependent Ca(2+) channel, CaV1.1, and used Ca(2+) imaging, western blotting, immunohistochemistry, proximity ligation assays, SUnSET analysis of protein synthesis, and Ca(2+) imaging techniques to define pathways modulated by Ca(2+) binding and/or permeation of CaV1.1. We also assessed fiber type distributions, cross-sectional area, and force frequency and fatigue in isolated muscles.Using mice with a pore mutation in CaV1.1 required for Ca(2+) binding and/or permeation (E1014K, EK), we demonstrate that CaV1.1 opening is coupled to CaMKII activation and refilling of sarcoplasmic reticulum Ca(2+) stores during sustained activity. Decreases in these Ca(2+)-dependent enzyme activities alter downstream signaling pathways (Ras/Erk/mTORC1) that lead to decreased muscle protein synthesis. The physiological consequences of the permeation and/or Ca(2+) binding defect in CaV1.1 are increased fatigue, decreased fiber size, and increased Type IIb fibers.While not essential for excitation-contraction coupling, Ca(2+) binding and/or permeation via the CaV1.1 pore plays an important modulatory role in muscle performance.