title: In vivo imaging of intracellular Ca2+ after muscle contractions and direct Ca2+ injection in rat skeletal muscle in diabetes.
abstract: The effects of muscle contractions on the profile of postcontraction resting intracellular Ca2+ ([Ca2+]i) accumulation in Type 1 diabetes are unclear. We tested the hypothesis that, following repeated bouts of muscle contractions, the rise in resting [Ca2+]i evident in healthy rats would be increased in diabetic rats and that these changes would be associated with a decreased cytoplasmic Ca2+ -buffering capacity. Adult male Wistar rats were divided randomly into diabetic (DIA; streptozotocin, ip) and healthy control (CONT) groups. Four weeks later, animals were anesthetized and spinotrapezius muscle contractions (10 sets of 50 contractions) were elicited by electrical stimulation (100 Hz). Ca2+ imaging was achieved using Fura-2 AM in the spinotrapezius muscle in vivo (i.e., circulation intact). The ratio (340/380 nm) was determined from fluorescence images following each set of contractions for estimation of [Ca2+]i. Also, muscle Ca2+ buffering was studied in individual myocytes microinjected with 2 mM Ca2+ solution. After muscle contractions, resting [Ca2+]i in DIA increased earlier and more rapidly than in CONT (P < 0.05 vs. precontraction). Peak [Ca2+]i in response to the Ca2+ injection was significantly higher in CONT (25.8 ± 6.0% above baseline) than DIA (10.2 ± 1.1% above baseline). Subsequently, CONT [Ca(2+)]i decreased rapidly (<15 s) to plateau 9-10% above baseline, whereas DIA remained elevated throughout the 60-s measurement window. No differences in SERCA1 and SERCA2 (Ca2+ uptake) protein levels were evident between CONT and DIA, whereas ryanodine receptor (Ca2+ release) protein level and mitochondrial oxidative enzyme activity (succinate dehydrogenase) were decreased in DIA (P < 0.05). In conclusion, diabetes impairs resting [Ca2+]i homeostasis following muscle contractions. Markedly different responses to Ca2+ injection in DIA vs. CONT suggest fundamentally deranged Ca2+ handling.
authors.affiliation: Department of Engineering Science, Bioscience and Technology Program, University of Electro-Communications, Tokyo, Japan;
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Eshima
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Tanaka
authors.forename: Takashi
authors.initials: T
authors.lastname: Sonobe
authors.forename: Tadakatsu
authors.initials: T
authors.lastname: Inagaki
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Nakajima
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 / Q000008:administration & dosage* / Q000378:metabolism*; D003920:Diabetes Mellitus / Q000503:physiopathology*; D007273:Injections, Intramuscular; D008297:Male; D057054:Molecular Imaging; D009119:Muscle Contraction / Q000187:drug effects*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000503:physiopathology*; D005082:Physical Exertion / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002118:Calcium
keywords: Fura-2 AM; calcium buffering; muscle contraction; spinotrapezius