ISSN:
1432-0878
Keywords:
Muscle extracellular compartments
;
Hypertonicity effects
;
Excitation-contraction coupling
;
Terminal cisternae
;
Caffeine contracture
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary Horseradish peroxidase, an extracellular marker, was given intravenously to frogs, and 40 min later the sartorius muscles were removed. The isolated muscles were exposed for an additional hour to Ringer solution containing peroxidase, then fixed with glutaraldehyde. Peroxidase activity was found in the T tubules, in some of the terminal cisternae (TC) of the SR, and occasionally in the longitudinal tubules of the SR. In transverse sections, the structures containing tracer formed a pattern of approximately parallel columns reaching to the cell surface; the statistical distribution of their spacing was nearly the same as that of the interdistances between the current-sensitive spots on the Z-line which triggered localized contraction (Huxley and Taylor, 1958). The caffeine contracture of frog sartorius muscles remained unchanged in isotonic Ringer solutions which were Ca++-free or contained Mn++ or La+++; however, contracture was blocked by prior exposure of the muscles to the same solutions made 2 × hypertonic with sucrose (known to produce swelling of T tubules and (TC). Since Mn++ and La+++ are known to depress Ca++ influx, these results suggest that washout of Ca++ from the TC, and penetration of La+++ or Mn++ into it, occur more rapidly due to the swelling of T tubules and TC associated with hypertonicity. It is concluded that at least some of the terminal cisternae are open to the interstitial fluid via the T tubules. Thus, depolarization of the T tubules could readly depolarize the cisternae and lead to Ca++ influx into the myoplasm.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00335454
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