Effects of beta-escin and saponin on the transverse-tubular system and sarcoplasmic reticulum membranes of rat and toad skeletal muscle

Launikonis, B. S. and Stephenson, D. G. (1999) Effects of beta-escin and saponin on the transverse-tubular system and sarcoplasmic reticulum membranes of rat and toad skeletal muscle. Pflugers Archiv European Journal of Physiology, 437 6: 955-965. doi:10.1007/s004240050867


Author Launikonis, B. S.
Stephenson, D. G.
Title Effects of beta-escin and saponin on the transverse-tubular system and sarcoplasmic reticulum membranes of rat and toad skeletal muscle
Journal name Pflugers Archiv European Journal of Physiology   Check publisher's open access policy
ISSN 0031-6768
1432-2013
Publication date 1999-04-01
Sub-type Article (original research)
DOI 10.1007/s004240050867
Volume 437
Issue 6
Start page 955
End page 965
Total pages 11
Place of publication Berlin / Heidelberg
Publisher Springer
Language eng
Abstract Mechanically skinned skeletal muscle fibres from rat and toad were exposed to the permeabilizing agents beta-escin and saponin. The effects of these agents on the sealed transverse tubular system (t-system) and sarcoplasmic reticulum (SR) were examined by looking at changes in the magnitude of the force responses to t-system depolarization, the time course of the fluorescence of fura-2 trapped in the sealed t-system, and changes in the magnitude of caffeine-induced contractures following SR loading with Ca2+ under defined conditions. In the presence of 2 mu g ml(-1) beta-escin and saponin, the response to t-system depolarization was not completely abolished, decreasing to a plateau, and a large proportion of fura-2 remained in the sealed t-system. At 10 mu g ml(-1), both agents abolished the ability of both rat and toad preparations to respond to t-system depolarization after 3 min of exposure, but a significant amount of fura-2 remained in sealed t-tubules even after exposure to 100 mu g ml(-1) beta-escin and saponin for 10 min. beta-Escin took longer than saponin to reduce the t-system depolarizations and fura-2 content of the sealed t-system to a similar level. The ability of the SR to load Ca2+ was reduced to a lower level after treatment with beta-escin than saponin. This direct effect on the SR occurred at much lower concentrations for rat (2 mu g ml(-1) beta-escin and 10 mu g ml(-1) saponin) than toad (10 mu g ml(-1) beta-escin and 150 mu g ml(-1) saponin). The reverse order in sensitivities to beta-escin and saponin of t-system and SR membranes indicates that the mechanisms of action of beta-escin and saponin are different in the two types of membrane. In conclusion, this study shows that: (1) beta-escin has a milder action on the surface membrane than saponin; (2) beta-escin is a more potent modifier of SR function; (3) simple permeabilization of membranes is not sufficient to explain the effects of beta-escin and saponin on muscle membranes; and (4) the t-system network within muscle fibres is not a homogeneous compartment.
Keyword Physiology
Beta-escin
Permeabilization
Saponin
Sarcoplasmic Reticulum
Skeletal Muscle
T-system
Induced Force Responses
Calcium Release
Smooth-muscle
Fibers
Depolarization
Channels
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 13 times in Thomson Reuters Web of Science Article | Citations
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Created: Mon, 13 Aug 2007, 21:03:32 EST