HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Launikonis, B. S. Articles by Stephenson, D. G. Search for Related Content PubMed PubMed Citation Articles by Launikonis, B. S. Articles by Stephenson, D. G.

Tubular system volume changes in twitch fibres from toad and rat skeletal muscle assessed by confocal microscopy

Bradley S. Launikonis and D. George Stephenson

The volume of the extracellular compartment (tubular system) within intact muscle fibres from cane toad and rat was measured under various conditions using confocal microscopy. Under physiological conditions at rest, the fractional volume of the tubular system (t-sys_Vol) was 1.38 ± 0.09 % (n = 17), 1.41 ± 0.09 % (n = 12) and 0.83 ± 0.07 % (n = 12) of the total fibre volume in the twitch fibres from toad iliofibularis muscle, rat extensor digitorum longus muscle and rat soleus muscle, respectively. In toad muscle fibres, the t-sys_Vol decreased by 30 % when the tubular system was fully depolarized and decreased by 15 % when membrane cholesterol was depleted from the tubular system with methyl--cyclodextrin but did not change as the sarcomere length was changed from 1.93 to 3.30 µm. There was also an increase by 30 % and a decrease by 25 % in t-sys_Vol when toad fibres were equilibrated in solutions that were 2.5-fold hypertonic and 50 % hypotonic, respectively. When the changes in total fibre volume were taken into consideration, the t-sys_Vol expressed as a percentage of the isotonic fibre volume did actually decrease as tonicity increased, revealing that the tubular system in intact fibres cannot be compressed below 0.9 % of the isotonic fibre volume. The results can be explained in terms of forces acting at the level of the tubular wall. These observations have important physiological implications showing that the tubular system is a dynamic membrane structure capable of changing its volume in response to the membrane potential, cholesterol depletion and osmotic stress but not when the sarcomere length is changed in resting muscle.

This article has been cited by other articles:

				O. Larina, P. Bhat, J. A. Pickett, B. S. Launikonis, A. Shah, W. A. Kruger, J. M. Edwardson, and P. Thorn Dynamic Regulation of the Large Exocytotic Fusion Pore in Pancreatic Acinar Cells Mol. Biol. Cell, September 1, 2007; 18(9): 3502 - 3511. [Abstract] [Full Text] [PDF]

				B. S. Launikonis and E. Rios Store-operated Ca2+ entry during intracellular Ca2+ release in mammalian skeletal muscle J. Physiol., August 15, 2007; 583(1): 81 - 97. [Abstract] [Full Text] [PDF]

				J. Zhou, B. S. Launikonis, E. Rios, and G. Brum Regulation of Ca2+ Sparks by Ca2+ and Mg2+ in Mammalian and Amphibian Muscle. An RyR Isoform-specific Role in Excitation-Contraction Coupling? J. Gen. Physiol., September 27, 2004; 124(4): 409 - 428. [Abstract] [Full Text] [PDF]

				B. S. Launikonis and D. G. Stephenson Osmotic Properties of the Sealed Tubular System of Toad and Rat Skeletal Muscle J. Gen. Physiol., February 23, 2004; 123(3): 231 - 247. [Abstract] [Full Text] [PDF]

				C. Goodman, M. Patterson, and G. Stephenson MHC-based fiber type and E-C coupling characteristics in mechanically skinned muscle fibers of the rat Am J Physiol Cell Physiol, June 1, 2003; 284(6): C1448 - C1459. [Abstract] [Full Text] [PDF]

				B. S. Launikonis, M. Barnes, and D. G. Stephenson Identification of the coupling between skeletal muscle store-operated Ca2+ entry and the inositol trisphosphate receptor PNAS, March 4, 2003; 100(5): 2941 - 2944. [Abstract] [Full Text] [PDF]