Frog alpha- and beta-ryanodine receptors provide distinct intracellular Ca2+ signals in a myogenic cell line.

• Main Authors: Taku Kashiyama, Takashi Murayama, Erika Suzuki, Paul D Allen, Yasuo Ogawa
• Format: Article
• Language: English
• Published: Public Library of Science (PLoS) 2010-07-01
• Series: PLoS ONE
• Online Access: http://europepmc.org/articles/PMC2902508?pdf=render

In frog skeletal muscle, two ryanodine receptor (RyR) isoforms, alpha-RyR and beta-RyR, are expressed in nearly equal amounts. However, the roles and significance of the two isoforms in excitation-contraction (E-C) coupling remains to be elucidated.In this study, we expressed either or both alpha-RyR and beta-RyR in 1B5 RyR-deficient myotubes using the herpes simplex virus 1 helper-free amplicon system. Immunological characterizations revealed that alpha-RyR and beta-RyR are appropriately expressed and targeted at the junctions in 1B5 myotubes. In Ca(2+) imaging studies, each isoform exhibited caffeine-induced Ca(2+) transients, an indicative of Ca(2+)-induced Ca(2+) release (CICR). However, the fashion of Ca(2+) release events was fundamentally different: alpha-RyR mediated graded and sustained Ca(2+) release observed uniformly throughout the cytoplasm, whereas beta-RyR supported all-or-none type regenerative Ca(2+) oscillations and waves. alpha-RyR but not beta-RyR exhibited Ca(2+) transients triggered by membrane depolarization with high [K(+)](o) that were nifedipine-sensitive, indicating that only alpha-RyR mediates depolarization-induced Ca(2+) release. Myotubes co-expressing alpha-RyR and beta-RyR demonstrated high [K(+)](o)-induced Ca(2+) transients which were indistinguishable from those with myotubes expressing alpha-RyR alone. Furthermore, procaine did not affect the peak height of high [K(+)](o)-induced Ca(2+) transients, suggesting minor amplification of Ca(2+) release by beta-RyR via CICR in 1B5 myotubes.These findings suggest that alpha-RyR and beta-RyR provide distinct intracellular Ca(2+) signals in a myogenic cell line. These distinct properties may also occur in frog skeletal muscle and will be important for E-C coupling.