IMR Press / FBL / Volume 7 / Issue 4 / DOI: 10.2741/ogawa

Frontiers in Bioscience-Landmark (FBL) is published by IMR Press from Volume 26 Issue 5 (2021). Previous articles were published by another publisher on a subscription basis, and they are hosted by IMR Press on imrpress.com as a courtesy and upon agreement with Frontiers in Bioscience.

Open Access Article
Ryanodine receptor isoforms of non-Mammalian skeletal muscle
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1 Department of Pharmacology, Juntendo University, Tokyo, Japan
Academic Editor:Hector Valdivia
Front. Biosci. (Landmark Ed) 2002, 7(4), 1184–1194; https://doi.org/10.2741/ogawa
Published: 1 May 2002
(This article belongs to the Special Issue The structure and function of calcium release channels)
Abstract

Whereas mammalian skeletal muscles express primarily a single isoform of ryanodine receptor (RyR) as the Ca2+ releasing channel, many non-mammalian vertebrate skeletal muscles express two isoforms in almost similar amount, alpha- and beta-RyR which are homologues of mammalian isoforms RyR1 and 3, respectively. alpha-RyR is believed to be directly involved in excitation-contraction coupling in skeletal muscles and is variable in its properties among animals and fibers, while beta-RyR shows similar properties and is variable in its content. alpha- and beta-RyR purified from frog skeletal muscle, a favorite material for physiological and morphological experiments, are very similar in Ca2+ dependent [3H]ryanodine binding. On the SR membrane, however, alpha-RyR is selectively suppressed in the ligand binding, indicating that the Ca2+-induced Ca2+ release (CICR) activity in skeletal muscle is conducted primarily by beta-RyR. We also stressed here that Ca2+ binding to the activating site is a necessary but not a sufficient condition for CICR. The maximum activity attainable under a specified condition is also a critical parameter to be determined. Taking these findings into consideration, we conclude that CICR is too slow to explain the physiological Ca2+ release on depolarization.

Keywords
Alpha-RyR
beta-RyR
Ca2+-induced Ca2+ release
Adenine Nucleotide
Caffeine
Review
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