Wakizaka Mario, Eshima Hiroaki, Tanaka Yoshinori, Shirakawa Hideki, Poole David C, Kano Yutaka
Department of Engineering Science, Bioscience and Technology Program, University of Electro-Communications, Chofu, Tokyo, Japan.
Department of Metabolism and Endocrinology, Juntendo University Graduate School of Medicine, Hongo, Tokyo, Japan.
Physiol Rep. 2017 Mar;5(5). doi: 10.14814/phy2.13180.
In contrast to cardiomyocytes, store overload-induced calcium ion (Ca) release (SOICR) is not considered to constitute a primary Ca releasing system from the sarcoplasmic reticulum (SR) in skeletal muscle myocytes. In the latter, voltage-induced Ca release (VICR) is regarded as the dominant mechanism facilitating contractions. Any role of the SOICR in the regulation of cytoplasmic Ca concentration ([Ca]) and its dynamics in skeletal muscle in vivo remains poorly understood. By means of in vivo single fiber Ca microinjections combined with bioimaging techniques, we tested the hypothesis that the [Ca] dynamics following Ca injection would be amplified and fiber contraction facilitated by SOICR. The circulation-intact spinotrapezius muscle of adult male Wistar rats (=34) was exteriorized and loaded with Fura-2 AM to monitor [Ca] dynamics. Groups of rats underwent the following treatments: (1) 0.02, 0.2, and 2.0 mmol/L Ca injections, (2) 2.0 mmol/L Ca with inhibition of ryanodine receptors (RyR) by dantrolene sodium (DAN), and (3) 2.0 mmol/L Ca with inhibition of SR Ca ATPase (SERCA) by cyclopiazonic acid (CPA). A quantity of 0.02 mmol/L Ca injection yielded no detectable response, whereas peak evoked [Ca] increased 9.9 ± 1.8% above baseline for 0.2 mmol/L and 23.8 ± 4.3% ( < 0.05) for 2.0 mmol/L Ca injections. The peak [Ca] in response to 2.0 mmol/L Ca injection was largely abolished by DAN and CPA (-85.8%, -71.0%, respectively, both < 0.05 vs. unblocked) supporting dependence of the [Ca] dynamics on Ca released by SOICR rather than injected Ca itself. Thus, this investigation demonstrates the presence of a robust SR-evoked SOICR operant in skeletal muscle in vivo.
与心肌细胞不同，储存过载诱导的钙离子（Ca）释放（SOICR）在骨骼肌细胞中不被认为是肌浆网（SR）的主要Ca释放系统。在骨骼肌细胞中，电压诱导的Ca释放（VICR）被视为促进收缩的主要机制。SOICR在体内骨骼肌细胞质Ca浓度（[Ca]）调节及其动力学中的任何作用仍知之甚少。通过体内单纤维Ca微量注射结合生物成像技术，我们检验了以下假设：Ca注射后的[Ca]动力学将被SOICR放大，并且纤维收缩会得到促进。将成年雄性Wistar大鼠（n = 34）的完整循环的斜方肌取出并加载Fura-2 AM以监测[Ca]动力学。大鼠分组接受以下处理：（1）注射0.02、0.2和2.0 mmol/L的Ca，（2）注射2.0 mmol/L的Ca并同时用丹曲林钠（DAN）抑制兰尼碱受体（RyR），（3）注射2.0 mmol/L的Ca并同时用环匹阿尼酸（CPA）抑制SR Ca ATP酶（SERCA）。注射0.02 mmol/L的Ca未产生可检测到的反应，而对于0.2 mmol/L的Ca注射，诱发的[Ca]峰值比基线升高9.9±1.8%，对于2.0 mmol/L的Ca注射则升高23.8±4.3%（P < 0.05）。DAN和CPA使对2.0 mmol/L Ca注射的[Ca]峰值大幅降低（分别为-85.8%、-71.0%，两者与未阻断组相比均P < 0.05），这支持了[Ca]动力学依赖于SOICR释放的Ca而非注射的Ca本身。因此，本研究证明了在体内骨骼肌中存在一种强大的由SR诱发的SOICR作用机制。
