Ion Transporters Involved in Dissipation of Transmembrane Na+ and K+ Gradients in C2C12 Myotubes Triggered by Electrical Pulse Stimulation

Abstract

Background/Aims: Cultured skeletal muscle cells subjected to electrical pulse stimulation (EPS) are widely employed as an in vitro model of exercising skeletal muscle. Numerous studies demonstrated that sustained excitation of skeletal muscle results in the dissipation of the transmembrane gradient of monovalent cations. During exercises the impending loss of excitability has to be counterbalanced by rapid restoration of the Na+i/K+i ratio. To understand mechanisms of the maintenance of muscle contractility, it is necessary to know which transporters are participated in the dissipation of Na+i and K+i gradients and how to activate Na,K-ATPase for its regeneration. This study was aimed at the identification of ion transporters involved in the dissipation of the transmembrane gradients of Na+ and K+induced by EPS, and Na,K-ATPase isoforms involved in its restoration. Methods: The differentiated C2C12 myotubes were subjected to electrical pulse stimulation in the presence or absence of different ion transport systems inhibitors followed by measurement of intracellular monovalent cations by flame atomic absorption spectrometry. Results: Electrical pulse stimulation of C2C12 myotubes results in the dissipation of Na+i/K+i gradient, which is maintained by α2-Na,K-ATPase. Na-K-2Cl cotransporter (NKCC), voltage-gated Na+ (Nav), and large conductance Ca2+-activated K+ channels (BKCa), and Na/H exchanger (NHE) are involved in the dissipation of this gradient. Suppression of calmodulin-dependent protein kinase II (CaMKII) increases Na+ efflux in EPS-treated C2C12 myotubes. Conclusion: NKCC, Nav, BKCa, and NHE are involved in the dissipation of Na+i/K+i gradient in EPS-treated C2C12 myotubes.