Effects of membrane cholesterol manipulation on excitation-contraction coupling in skeletal muscle of the toad

Launikonis, Bradley S. and Stephenson, D. George (2001) Effects of membrane cholesterol manipulation on excitation-contraction coupling in skeletal muscle of the toad. Journal of Physiology, 534 1: 71-85. doi:10.1111/j.1469-7793.2001.00071.x


Author Launikonis, Bradley S.
Stephenson, D. George
Title Effects of membrane cholesterol manipulation on excitation-contraction coupling in skeletal muscle of the toad
Journal name Journal of Physiology   Check publisher's open access policy
ISSN 0022-3751
Publication date 2001-07-01
Sub-type Article (original research)
DOI 10.1111/j.1469-7793.2001.00071.x
Volume 534
Issue 1
Start page 71
End page 85
Total pages 15
Place of publication Oxford, England
Publisher Blackwell for the Physiological Society
Language eng
Subject 11 Medical and Health Sciences
Formatted abstract
1.
Single mechanically skinned fibres and intact bundles of fibres from the twitch region of the iliofibularis muscle of cane toads were used to investigate the effects of membrane cholesterol manipulation on excitation-contraction (E-C) coupling. The cholesterol content of membranes was manipulated with methyl-β-cyclodextrin (MβCD).
 
2.

In mechanically skinned fibres, depletion of membrane cholesterol with MβCD caused a dose- and time-dependent decrease in transverse tubular (t)-system depolarization-induced force responses (TSDIFRs). TSDIFRs were completely abolished within 2 min in the presence of 10 mm MβCD but were not affected after 2 min in the presence of a 10 mm MβCD-1 mm cholesterol complex. There was a very steep dependence between the change in TSDIFRs and the MβCD : cholesterol ratio at 10 mm MβCD, indicating that the inhibitory effect of MβCD was due to membrane cholesterol depletion and not to a pharmacological effect of the agent. Tetanic responses in bundles of intact fibres were abolished after 3-4 h in the presence of 10 mm MβCD.

3.

The duration of TSDIFRs increased markedly soon (< 2 min) after application of 10 mm MβCD and 10 mm MβCD-cholesterol complexes, but the Ca2+ activation properties of the contractile apparatus were minimally affected by 10 mm MβCD. The Ca2+ handling abilities of the sarcoplasmic reticulum appeared to be modified after 10 min exposure to 10 mm MβCD.

4.

Confocal laser scanning microscopy revealed that the integrity of the t-system was not compromised by either intra- or extracellular application of 10 mm MβCD and that a large [Ca2+] gradient was maintained across the t-system.

5.

Membrane cholesterol depletion caused rapid depolarization of the polarized t-system as shown independently by spontaneous TSDIFRs induced by MβCD and by changes in the fluorescence intensity of an anionic potentiometric dye (DiBAC4(3)) in the presence of MβCD. This rapid depolarization of the t-system by cholesterol depletion was not prevented by blocking the Na+ channels with TTX (10 μm) or the L-type Ca2+ channels with Co2+ (5 mm).

6.

The results demonstrate that cholesterol is important for maintaining the functional integrity of the t-system and sarcoplasmic reticulum, probably by having specific effects on different membrane proteins that may be directly or indirectly involved in E-C coupling.
Keyword Physiology
Atp Hydrolyzing Activity
Sarcoplasmic-reticulum
Human-erythrocyte
Force Responses
Calcium Release
Fibers
Rat
Cells
Saponin
Cyclodextrins
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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Citation counts: TR Web of Science Citation Count  Cited 27 times in Thomson Reuters Web of Science Article | Citations
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Created: Thu, 26 Jun 2008, 19:31:01 EST by Sophie Jordan on behalf of School of Biomedical Sciences