Volume changes of the myosin lattice resulting from repetitive stimulation of single muscle fibers.
Single muscle fibers at 1 degreesC were subjected to brief tetani (20 Hz) at intervals of between 20 s and 300 s over a period of up to 2 h. A band lattice spacing increased during this period at a rate inversely dependent on the rest interval between tetani. Spacing increased rapidly during the first 10 tetani at a rate equivalent to the production of 0.04 mOsmol.liter-1 of osmolyte per contraction, then continued to expand at a much slower rate. For short rest intervals, where lattice expansion was largest, spacing increased to a limiting value between 46 and 47 nm (sarcomere length 2.2 micrometer), corresponding to accumulation of 30 mOsmol.liter-1 of osmolytes, where it remained constant until repetitive stimulation was terminated. At this limiting spacing, force was reduced by up to 30%. The effect of lattice swelling on the lattice compression that accompanies isometric force recovery from unloaded shortening was to increase the compression, similar to that observed in hypotonic media at a similar spacing. During recovery from repetitive stimulation, spacing recompressed to its original value with a half-time of 15-30 min. These findings suggest that mechanical activity produces an increase in osmotic pressure within the cell as a result of product accumulation from cross-bridge and sarcoplasmic reticulum ATPases and glycolysis.
Rapp
G
G
EMBL Outstation, Deutsches Elektronen-Synchrotron, D-22603 Hamburg, Germany.
Ashley
C C
CC
Bagni
M A
MA
Griffiths
P J
PJ
Cecchi
G
G
D000818:Animals; D001696:Biomechanical Phenomena; D055592:Biophysical Phenomena; D001703:Biophysics; D003198:Computer Simulation; D004558:Electric Stimulation; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D009218:Myosins / Q000737:chemistry* / Q000502:physiology*; D009997:Osmotic Pressure; D011896:Rana temporaria
D009218:Myosins