Open AccessIn vivo Ca 2+ dynamics induced by Ca 2+ injection in individual rat skeletal muscle fibers
Author(s) -
Wakizaka Mario,
Eshima Hiroaki,
Tanaka Yoshinori,
Shirakawa Hideki,
Poole David C.,
Kano Yutaka
Publication year - 2017
Publication title -
physiological reports
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.918
H-Index - 39
ISSN - 2051-817X
DOI - 10.14814/phy2.13180
Subject(s) - cyclopiazonic acid , ryanodine receptor , skeletal muscle , calcium , in vivo , dantrolene sodium , chemistry , medicine , serca , endocrinology , endoplasmic reticulum , myocyte , calcium metabolism , dantrolene , atpase , biology , biochemistry , microbiology and biotechnology , enzyme
In contrast to cardiomyocytes, store overload‐induced calcium ion (Ca 2+ ) release (SOICR) is not considered to constitute a primary Ca 2+ releasing system from the sarcoplasmic reticulum (SR) in skeletal muscle myocytes. In the latter, voltage‐induced Ca 2+ release (VICR) is regarded as the dominant mechanism facilitating contractions. Any role of the SOICR in the regulation of cytoplasmic Ca 2+ concentration ([Ca 2+ ] i ) and its dynamics in skeletal muscle in vivo remains poorly understood. By means of in vivo single fiber Ca 2+ microinjections combined with bioimaging techniques, we tested the hypothesis that the [Ca 2+ ] i dynamics following Ca 2+ 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 [Ca 2+ ] i dynamics. Groups of rats underwent the following treatments: (1) 0.02, 0.2, and 2.0 mmol/L Ca 2+ injections, (2) 2.0 mmol/L Ca 2+ with inhibition of ryanodine receptors (RyR) by dantrolene sodium (DAN), and (3) 2.0 mmol/L Ca 2+ with inhibition of SR Ca 2+ ATPase (SERCA) by cyclopiazonic acid (CPA). A quantity of 0.02 mmol/L Ca 2+ injection yielded no detectable response, whereas peak evoked [Ca 2+ ] i increased 9.9 ± 1.8% above baseline for 0.2 mmol/L and 23.8 ± 4.3% ( P < 0.05) for 2.0 mmol/L Ca 2+ injections. The peak [Ca 2+ ] i in response to 2.0 mmol/L Ca 2+ injection was largely abolished by DAN and CPA (−85.8%, −71.0%, respectively, both P < 0.05 vs. unblocked) supporting dependence of the [Ca 2+ ] i dynamics on Ca 2+ released by SOICR rather than injected Ca 2+ itself. Thus, this investigation demonstrates the presence of a robust SR‐evoked SOICR operant in skeletal muscle in vivo.