Acute Elevated Glucose Promotes Abnormal Action Potential-Induced Ca Transients in Cultured Skeletal Muscle Fibers.

A common comorbidity of diabetes is skeletal muscle dysfunction, which leads to compromised physical function. Previous studies of diabetes in skeletal muscle have shown alterations in excitation-contraction coupling (ECC)-the sequential link between action potentials (AP), intracellular Ca release, and the contractile machinery. Yet, little is known about the impact of acute elevated glucose on the temporal properties of AP-induced Ca transients and ionic underlying mechanisms that lead to muscle dysfunction. Here, we used high-speed confocal Ca imaging to investigate the temporal properties of AP-induced Ca transients, an intermediate step of ECC, using an acute in cellulo model of uncontrolled hyperglycemia (25 mM, 48 h.). Control and elevated glucose-exposed muscle fibers cultured for five days displayed four distinct patterns of AP-induced Ca transients (phasic, biphasic, phasic-delayed, and phasic-slow decay); most control muscle fibers show phasic AP-induced Ca transients, while most fibers exposed to elevated D-glucose displayed biphasic Ca transients upon single field stimulation. We hypothesize that these changes in the temporal profile of the AP-induced Ca transients are due to changes in the intrinsic excitable properties of the muscle fibers. We propose that these changes accompany early stages of diabetic myopathy.