%0 Journal Article
%T In vivo Ca2+ dynamics induced by Ca2+ injection in individual rat skeletal muscle fibers
%A David C. Poole
%A Hideki Shirakawa
%A Hiroaki Eshima
%A Mario Wakizaka
%A Yoshinori Tanaka
%A Yutaka Kano
%J Archive of "Physiological Reports".
%D 2017
%R 10.14814/phy2.13180
%X In contrast to cardiomyocytes, store overload©\induced calcium ion (Ca2+) release (SOICR) is not considered to constitute a primary Ca2+ releasing system from the sarcoplasmic reticulum (SR) in skeletal muscle myocytes. In the latter, voltage©\induced Ca2+ release (VICR) is regarded as the dominant mechanism facilitating contractions. Any role of the SOICR in the regulation of cytoplasmic Ca2+ concentration ([Ca2+]i) and its dynamics in skeletal muscle in vivo remains poorly understood. By means of in vivo single fiber Ca2+ microinjections combined with bioimaging techniques, we tested the hypothesis that the [Ca2+]i dynamics following Ca2+ injection would be amplified and fiber contraction facilitated by SOICR. The circulation©\intact spinotrapezius muscle of adult male Wistar rats (n = 34) was exteriorized and loaded with Fura©\2 AM to monitor [Ca2+]i dynamics. Groups of rats underwent the following treatments: (1) 0.02, 0.2, and 2.0 mmol/L Ca2+ injections, (2) 2.0 mmol/L Ca2+ with inhibition of ryanodine receptors (RyR) by dantrolene sodium (DAN), and (3) 2.0 mmol/L Ca2+ with inhibition of SR Ca2+ ATPase (SERCA) by cyclopiazonic acid (CPA). A quantity of 0.02 mmol/L Ca2+ injection yielded no detectable response, whereas peak evoked [Ca2+]i increased 9.9 ¡À 1.8% above baseline for 0.2 mmol/L and 23.8 ¡À 4.3% (P < 0.05) for 2.0 mmol/L Ca2+ injections. The peak [Ca2+]i in response to 2.0 mmol/L Ca2+ injection was largely abolished by DAN and CPA (£¿85.8%, £¿71.0%, respectively, both P < 0.05 vs. unblocked) supporting dependence of the [Ca2+]i dynamics on Ca2+ released by SOICR rather than injected Ca2+ itself. Thus, this investigation demonstrates the presence of a robust SR©\evoked SOICR operant in skeletal muscle in vivo
%K Ca2+©\induced Ca2+ release
%K ryanodine receptor
%K sarcoplasmic reticulum
%K store overload©\induced Ca2+ release
%U https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5350183/