Effects of Mg2+ on Ca2+ release from sarcoplasmic reticulum of skeletal muscle fibres from yabby (crustacean) and rat

Launikonis, Bradley S. and Stephenson, D. George (2000) Effects of Mg2+ on Ca2+ release from sarcoplasmic reticulum of skeletal muscle fibres from yabby (crustacean) and rat. Journal of Physiology, 526 2: 299-312. doi:10.1111/j.1469-7793.2000.00299.x


Author Launikonis, Bradley S.
Stephenson, D. George
Title Effects of Mg2+ on Ca2+ release from sarcoplasmic reticulum of skeletal muscle fibres from yabby (crustacean) and rat
Journal name Journal of Physiology   Check publisher's open access policy
ISSN 0022-3751
Publication date 2000-07-01
Sub-type Article (original research)
DOI 10.1111/j.1469-7793.2000.00299.x
Volume 526
Issue 2
Start page 299
End page 312
Total pages 14
Place of publication Oxford
Publisher Blackwell for the Physiological Society
Language eng
Abstract 1. The role of myoplasmic [Mg2+] on Ca2+ release from the sarcoplasmic reticulum (SR) was examined in the two major types of crustacean muscle fibres, the tonic, long sarcomere fibres and the phasic, short sarcomere fibres of the fresh mater decapod crustacean Cherax: destructor (yabby) and in the fast-twitch rat muscle fibres using the mechanically skinned muscle fibre preparation. 2. A robust Ca2+-induced Ca2+-release (CICR) mechanism was present in both long and short sarcomere fibres and 1 mM Mg2+ exerted a strong inhibitory action on the XR Ca2+ release in both fibre types. 3. The XR displayed different properties with respect to Ca2+ loading in the long and the short sarcomere fibres and marked functional differences were identified with respect to Mg2+ inhibition between the two crustacean fibre types. Thus, in long sarcomere fibres, the submaximally loaded XR was able to release Ca2+ when [Mg2+] was lowered from 1 to 0.01 mw in the presence of 8 mM ATP(total) and in the virtual absence of Ca2+ (< 5 nM) even when the CICR was suppressed. In contrast, negligible Ca2+ was released from the submaximally loaded SR of short sarcomere yabby fibres when [Mg2+] was lowered from 1. to 0.01 mM under the same conditions as for the long sarcomere fibres. Nevertheless, the rate of XR Ca2+ release in short sarcomere fibres increased markedly when [Mg2+] was lowered in the presence of [Ca2+] approaching the normal resting levels (50-100 nM). 4. Rat fibres were able to release SR Ca2+ at a faster rate than the long sarcomere yabby fibres when [Mg2+] was lowered from 1 to 0.01 mM in the virtual absence of Ca2+ but, unlike with yabby fibres, the net rate of Ca2+ release was actually increased for conditions that were considerably less favourable to CICR. 5. In summary it is concluded that crustacean skeletal muscles have more that one functional type of Ca2+-release channels, that these channels display properties that are intermediate between those of mammalian skeletal and cardiac isoforms, that the inhibition exerted by Mg2+ at rest on the crustacean SR Ca2+-release channels must be removed during excitation-contraction coupling and that, unlike in crustacean fibres, CICR cannot play the major role in the activation of XR Ca2+-release channels in the rat skeletal muscle.
Keyword Physiology
Channel Ryanodine Receptor
Calcium-release
Activation Properties
Adenine-nucleotides
Crayfish Muscle
Fibers
Caffeine
Toad
Depolarization
Inactivation
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Biomedical Sciences Publications
 
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Created: Mon, 13 Aug 2007, 21:54:28 EST