MYOFILAMENT OVERLAP IN SWIMMING CARP .1. MYOFILAMENT LENGTHS OF RED AND WHITE MUSCLE

To assess myofilament overlap during locomotion, we estimated the length of myosin and actin filaments in axial red and white muscle of carp. Myosin filament lengths were 1.52 +/- 0.009 and 1.50 +/- 0.037-mu-m (means +/- SD) in the red and white muscle, respectively, as measured from thin sections. After correction for shrinkage (using the troponin-based 385-angstrom axial periodicity), thin filaments were 0.96 +/- 0.009 and 0.97 +/- 0.023-mu-m in the red and white muscles, respectively. Filaments were also isolated from the white muscle and negatively stained. Myosin filaments were 1.56 +/- 0.025-mu-m, and actin filaments were 0.99 +/- 0.024-mu-m in length. The data from thin sections and isolated filaments agreed within 2% for actin and 4% for myosin filaments. The number of actin filament periods (24 for the red and white muscle) and the length of the filaments are the same as in frog. This suggests that the classic sarcomere length-tension curve of frog muscle may be used to estimate the functional properties of carp red and white muscle.