Intracellular calcium accumulation following eccentric contractions in rat skeletal muscle in vivo: role of stretch-activated channels.
Although the accumulation of intracellular calcium ions ([Ca2+]i) is associated with muscle damage, little is known regarding the temporal profile of muscle [Ca2+]i under in vivo conditions, and, specifically, the effects of different contraction types [e.g., isometric (ISO); eccentric (ECC)] on [Ca2+]i remain to be determined. The following hypotheses were tested. 1) For 90 min at rest, an in vivo vs. in vitro preparation would better maintain initial [Ca2+]i. 2) Compared with ISO, ECC contractions (50 contractions, 10 sets, 5-min interval) would lead to a greater increase of [Ca2+]i. 3) Elevated [Ca2+]i during ECC would be reduced or prevented by the stretch-activated ion channel blockers streptomycin and gadolinium (Gd3+). Spinotrapezius muscles of Wistar rats were exteriorized (in vivo) or excised (in vitro). [Ca2+]i was evaluated by loading the muscle with fura 2-AM using fluorescence imaging. [Ca2+]i rose progressively beyond 40 min at rest under in vitro but not in vivo conditions during the 90-min protocol. In vivo [Ca2+]i increased more rapidly during ECC (first set) than ISO (fifth set) (P < 0.05 vs. precontraction values). The peak level of [Ca2+]i was increased by 21.5% (ISO) and 42.8% (ECC) after 10 sets (both P < 0.01). Streptomycin and Gd3+ abolished the majority of [Ca2+]i increase during ECC (69 and 86% reduction, respectively; P < 0.01 from peak [Ca2+]i of ECC). In conclusion, in vivo quantitative analyses demonstrated that ECC contractions elevate [Ca2+]i significantly more than ISO contractions and that stretch-activated channels may play a permissive role in this response.
Sonobe
Takashi
T
Department of Applied Physics and Chemistry, University of Electro-Communications, Chofu, Tokyo 1828585, Japan.
Inagaki
Tadakatsu
T
Poole
David C
DC
Kano
Yutaka
Y
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005682:Gadolinium / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007537:Isometric Contraction; D007700:Kinetics; D008297:Male; D049990:Membrane Transport Modulators / Q000494:pharmacology; D008856:Microscopy, Fluorescence; D018715:Microscopy, Video; D009119:Muscle Contraction / Q000187:drug effects; D009470:Muscle Spindles / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012107:Research Design; D013307:Streptomycin / Q000494:pharmacology; D015854:Up-Regulation
D007473:Ion Channels; D049990:Membrane Transport Modulators; D005682:Gadolinium; D002118:Calcium; D013307:Streptomycin