Gender Influence on Muscular Ca2+ Accumulation Pattern Following Repeated Bout of Isometric Contractions in Rat

Abstract

Female muscles have been found to be more fatigue resistant and to recover faster than male muscles. The mechanisms behind these differences in skeletal muscle are still unclear, but it is likely that they are as consequences of different sex hormonal status, fiber type composition and therefore Ca2+ handling may different. PURPOSE: To explore the role of Ca2+ on skeletal muscle function following isometric tetanic contractions in the rat spinotrapezius muscle in vivo. We tested the hypothesis that Ca2+ accumulation following fatiguing contractions would be different between sexes due to estrogen level or skeletal muscle fiber type composition. METHOD: The intact spinotrapezius muscle of adult male, female and ovariectomized (OVX) female Wistar rats was exteriorized. Tetanic isometric contractions (100 Hz, 700 ms duration, 20 times per minute for a total of 10 sets of 50 contractions) were elicited by surface electrical stimulation. Using Fura2-AM, the fluorescence ratio (340/380 nm) was used to estimate [Ca2+]i and changes thereof. Spinotrapezius muscle were removed and prepared for histochemistry. RESULT: Muscle force production was significantly decreased within each set of contractions for all groups (Male: -68.8%, Female: -40.0%, OVX: -42.9% at last contraction of 10th set vs. the initial force). Following isometric contractions [Ca2+]i increased significantly in male (18.9 ± 4.6%) but not in female (2.8 ± 2.0%) and OVX (3.8 ± 2.3%) that remained significantly reduced compared with males. Slow twitch fiber composition were similar in each group (Male: 44 ± 2%, Female: 44 ± 1%, OVX: 51 ± 1%). CONCLUSION: These results demonstrate that females maintain [Ca2+]i homeostasis following isometric contractions. The presence of normal estrogen levels and muscle fiber type are not obligatory for the difference between genders.