title: Sex differences in intracellular Ca(2+) accumulation following eccentric contractions of rat skeletal muscle in vivo.
abstract: It is commonly believed that estrogen and sex influences play significant effects in skeletal muscle damage following eccentric exercise. The mechanistic bases for this sex-specific phenomenon remain to be resolved. The muscle damage has been linked to loss of Ca(2+) homeostasis and resultant intramyocyte Ca(2+) ([Ca(2+)](i)) accumulation; therefore, we tested the hypothesis that the greater eccentric exercise-induced muscle damage in males would be associated with more pronounced [Ca(2+)](i) accumulation. The intact spinotrapezius muscle of adult Wistar rats [male, female, and ovariectomized (OVX)-to investigate the effects of estrogen] was exteriorized. Tetanic eccentric contractions (100 Hz, 700-ms duration, 20 contractions/min for a total of 10 sets of 50 contractions) were elicited by electrical stimulation during synchronized muscle stretch of 10% resting muscle length. The fluorescence ratio (F(340)/F(380) nm) was determined from images captured following each set of contractions, and fura-2 AM was used to estimate [Ca(2+)](i) and changes thereof. Following eccentric contractions, [Ca(2+)](i) increased significantly in male (42.8 ± 5.3%, P < 0.01) but not in female (9.4 ± 3.5%) rats. OVX evidenced an intermediate response (17.0 ± 1.2%) that remained significantly reduced compared with males. These results demonstrate that females maintain [Ca(2+)](i) homeostasis following novel eccentric contractions, whereas males do not, which is consistent with a role for elevated [Ca(2+)](i) in eccentric exercise-induced muscle damage. The presence of normal estrogen levels is not obligatory for the difference between the sexes.
authors.affiliation: Dept. of Engineering Science, Univ. of Electro-Communications Chofu, Tokyo, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Sonobe
authors.forename: Tadakatsu
authors.initials: T
authors.lastname: Inagaki
authors.forename: Mizuki
authors.initials: M
authors.lastname: Sudo
authors.forename: David C
authors.initials: DC
authors.lastname: Poole
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Kano
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002154:Calpain / Q000378:metabolism; D004958:Estradiol / Q000378:metabolism; D030762:Estrous Cycle / Q000502:physiology; D005260:Female; D007091:Image Processing, Computer-Assisted; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D008856:Microscopy, Fluorescence; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000473:pathology; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000293:injuries / Q000378:metabolism* / Q000473:pathology; D010052:Ovariectomy; D010805:Physical Conditioning, Animal / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012727:Sex Characteristics
chemical_list: D007527:Isoenzymes; D009124:Muscle Proteins; D004958:Estradiol; D002154:Calpain; C491372:Capn3 protein, rat; D002118:Calcium