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1 Department of Applied Physics and Chemistry, University of Electro-Communications, Chofu, Tokyo, Japan
2 Department of Kinesiology, Anatomy & Physiology, Kansas State University, Manhattan, Kansas, United States
3 Department of Appled Physics and Chemistry, University of Electro-Communications, Chofu, Tokyo, Japan
* To whom correspondence should be addressed. E-mail: kano{at}pc.uec.ac.jp.
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 times, 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 channels (SAC) blocker 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 Fura2-AM and using a 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. pre-contraction 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). 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.
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