Correlation of structure, speed of contraction, and total tension in fast and slow abdominal muscle fibers of the lobster (<i>Homarus americanus</i>)

Abstract

Abstract The fibers in the deep and superficial extensor muscles of the lobster abdomen differ in structural and physiological characteristics. The superficial extensor muscle fibers have relatively long (&gt; 6 μ) sarcomeres, in which thin and thick myofilaments overlap for about 3 μ per half‐sarcomere at rest length. The deep extensor muscle fibers have relatively short (&lt; 4 μ) sarcomeres, in which the region of overlap is about 1.5 μ per half‐sarcomere at rest length. The ratio of thin to thick filaments is 6:1 in the superficial muscle fibers and 3:1 in the deep muscle fibers. Contraction and relaxation are much more rapid in the deep muscle fibers. The superficial muscle fibers develop substantially more tension than the deep muscle fibers in high K + , in caffeine, in high K + plus caffeine, and during prolonged spikes in solutions containing tetraethylammonium chloride. The results are consistent with the predictions of the sliding filament hypothesis of muscle contraction.