Equivalent L-type channel (Ca_V1.1) function in adult female and male mouse skeletal muscle fibers.

Loss of total muscle force during aging has both atrophic and non-atrophic components. The former deficit is a direct consequence of reduced muscle mass while the latter has been attributed to a depression of excitation-contraction (EC) coupling. It is well established that age-onset reductions in sex hormone production regulate the atrophic component in both males and females. However, it is unknown whether the non-atrophic component is influenced by sex hormones. Since the non-atrophic component has been linked mechanistically to reduced expression of the skeletal muscle L-type Ca²⁺ channel (Ca_V1.1), we recorded L-type Ca²⁺ currents, gating charge movements and depolarization-induced changes in myoplasmic Ca²⁺ from flexor digitorum brevis (FDB) fibers of naïve and gonadectomized mice of both sexes. Our first set of experiments sought to identify any basal differences in EC coupling or L-type Ca²⁺ flux between the sexes; no detectable differences in any of the aforementioned parameters were observed between FDB harvested from either naïve males or females. In the latter segments of the study, ovariectomy (OVX) and orchiectomy (ORX) models were used to assess the possible influence of sex hormones on EC coupling and/or L-type Ca²⁺ flux. In these experiments, FDB fibers harvested from OVX and ORX mice both showed no differences in L-type Ca²⁺ current, gating charge movement or depolarization-induced changes in Ca²⁺ release from the sarcoplasmic reticulum. Taken together, our results indicate L-type Ca²⁺ channel function and EC coupling are: 1) equivalent between the sexes, and 2) not significantly regulated by sex hormones. Since recent NIH review guidelines mandate the consideration of sex differences as a criterion for review, our work indicates the suitability of either sex for the study of the fundamental mechanisms of EC coupling. Thus, our findings may accelerate the research process by conserving animals, labor and financial resources. Copyright © 2019 Elsevier Inc. All rights reserved.

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