AJP - Regulatory, Integrative and Comparative Physiology, Vol 242, Issue 3 394-R400, Copyright © 1982 by American Physiological Society
Energy utilization by Limulus telson muscle at different sarcomere and A-band lengths
S. Davidheiser and R. E. Davies
Phosphorylargnine utilization (delta PArg) was determined in isolated
Limulus telson muscle during isometric and isovelocity contractions at
long, intermediate, and short lengths when thick filaments were either long
and staggered, long and aligned, or shortened. Muscles developed 30% of
maximum force at a length of 0.5 Lo (Lo 7 micrometers sarcomere length)
during isometric tetani of 5, 15, and 30 s; however, the rate of delta PArg
was the same in both the 0.5 Lo and Lo groups. External force and delta
PArg were both less during isometric tetani at lengths of 1.7 and 2.0 Lo
compared with the values at Lo, as expected due to a reduction in
thick-thin filament overlap. However, at lengths of 0.6 and 0.3 Lo delta
PArg was the same as at Lo despite a decrease in external isometric
tension. No significant delta PArg was measured when telson muscles
shortened rapidly (0.8 Vmax) at long or short lengths indicating the thick
filament shortening per se required little, if any, energy expenditure. The
overall chemical efficiency of telson muscles for performing external work
during slow isovelocity contractions was 31% in groups shortening
equivalent distances (0.5 Lo) from starting lengths of 1.6 and 1.3 Lo and
15% in the group shortening from 1.1 Lo.
