Osmotic properties of the sealed tubular system of toad and rat skeletal muscle

Launikonis, B. S. and Stephenson, D. G. (2004) Osmotic properties of the sealed tubular system of toad and rat skeletal muscle. Journal of General Physiology, 123 3: 231-247. doi:10.1085/jgp.200308946

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Author Launikonis, B. S.
Stephenson, D. G.
Title Osmotic properties of the sealed tubular system of toad and rat skeletal muscle
Journal name Journal of General Physiology   Check publisher's open access policy
ISSN 0022-1295
Publication date 2004-01-01
Sub-type Article (original research)
DOI 10.1085/jgp.200308946
Open Access Status File (Publisher version)
Volume 123
Issue 3
Start page 231
End page 247
Total pages 17
Place of publication New York
Publisher Rockefeller University Press
Language eng
Abstract A method was developed that allows conversion of changes in maximum Ca2+-dependent fluorescence of a fixed amount of fluo-3 into volume changes of the fluo-3-containing solution. This method was then applied to investigate by confocal microscopy the osmotic properties of the sealed tubular (t-) system of toad and rat mechanically skinned fibers in which a certain amount Of fluo-3 was trapped. When the osmolality of the myoplasmic environment was altered by simple dilution or addition of sucrose within the range 190-638 mosmol kg(-1), the sealed t-system of toad fibers behaved almost like an ideal osmometer, changing its volume inverse proportionally to osmolality However, increasing the osmolality above 638 to 2,550 mosmol kg(-1) caused hardly any change in t-system volume. In myoplasmic solutions made hypotonic to 128 mosmol kg(-1), a loss of Ca2+ from the sealed t-system of toad fibers Occurred, presumably through either stretch-activated cationic channels or store-operated Ca2+ channels. In contrast to the behavior of the t-system in toad fibers, the volume of the sealed t-system of rat fibers changed little (by <20%) when the osmolality of the myoplasmic environment changed between 210 and 2,800 mosmol kg(-1). Results were also validated with calcein. Clear differences between rat and toad fibers were also found with respect to the t-system permeability for glycerol. Thus, glycerol equilibrated across the rat t-system within seconds to minutes, but was not equilibrated across the t-system of toad fibers even after 20 min. These results have broad implications for understanding osmotic properties of the t-system and reversible vacuolation in muscle fibers. Furthermore, we observed for the first time in mammalian fibers an orderly lateral shift of the t-system networks whereby t-tubule networks to the left of the Z-line crossover to become t-tubule networks to the right of the Z-line in the adjacent sarcomere (and vice versa). This orderly rearrangement can provide a pathway for longitudinal continuity of the t-system along the fiber axis.
Keyword Physiology
Skeletal Muscle
Osmotic Gradient
Skinned Fibers
Frog Sartorius
Reversible Vacuolation
Transverse Tubules
Proximal Tubule
Water Channels
Twitch Fibers
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
School of Biomedical Sciences Publications
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Created: Tue, 14 Aug 2007, 00:10:15 EST