Intracellular calcium accumulation following eccentric contractions in rat skeletal muscle in vivo: role of stretch-activated channels

摘要

Although the accumulation of intracellular calcium ions ([Ca~(2+)]_i) is associated with muscle damage, little is known regarding the temporal profile of muscle [Ca~(2+)]_i under in vivo conditions, and, specifically, the effects of different contraction types [e.g., isometric (ISO); eccentric (ECC)] on [Ca~(2+)]_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 [Ca~(2+)]_i. 2) Compared with ISO, ECC contractions (50 contractions, 10 sets, 5-min interval) would lead to a greater increase of [Ca~(2+)]_i. 3) Elevated [Ca~(2+)]_i during ECC would be reduced or prevented by the stretch-activated ion channel blockers streptomycin and gadolinium (Gd~(3+)). Spinotrapezius muscles of Wistar rats were exteriorized (in vivo) or excised (in vitro). [Ca~(2+)]_i was evaluated by loading the muscie with fura 2-AM using fluorescence imaging. [Ca~(2+)]_i rose progressively beyond 40 min at rest under in vitro but not in vivo conditions during the 90-min protocol. In vivo [Ca~(2+)]_i increased more rapidly during ECC (first set) than ISO (fifth set) (P < 0.05 vs. precontraction values). The peak level of [Ca~(2+)]_i was increased by 21.5% (ISO) and 42.8% (ECC) after 10 sets (both P < 0.01). Streptomycin and Gd~(3+) abolished the majority of [Ca~(2+)]_i increase during ECC (69 and 86% reduction, respectively; P < 0.01 from peak [Ca~(2+)]_i of ECC). In conclusion, in vivo quantitative analyses demonstrated that ECC contractions elevate [Ca~(2+)]_i significantly more than ISO contractions and that stretch-activated channels may play a permissive role in this response.