NONUNIFORMITY OF SARCOMERE LENGTHS CAN EXPLAIN THE CATCH-LIKE EFFECT OF ARTHROPOD MUSCLE

The 'catch-like' effect, a hysteresis phenomenon in arthropod skeletal muscle contraction thought to be related to the catch of molluscan sm ooth muscle, was investigated in the closer muscle of the crab Eriphia spinifrons. Several parameters were varied to determine their influen ce on the catch-like effect. These parameters were (1) the frequency o f repetitive stimulation of the slow excitatory neuron, (2) additional stimulation of: the inhibitory neuron, (3) the amount of stretch appl ied to the muscle and (4) the stiffness of the mechano-electrical tran sducer. The results show that the catch-like effect is not related to the catch of molluscan smooth muscle but rather to the 'residual force enhancement' or 'creep' phenomenon described for vertebrate muscle. A hypothesis for residual force enhancement implies that the increase i n force is caused by non-uniformity of sarcomere lengths along the mus cle fibre. Based on this hypothesis and the actual force-length relati onship of the crab muscle studied, calculations were carried out to de termine, if the observed catch-like effect can be explained by such a model. The calculations corroborate the experimental evidence. The cat ch-like effect of arthropod muscles can thus be explained by the same mechanism responsible for residual force enhancement and creep in vert ebrate muscle. A physiological relevance of the catch-like effect in a rthropod muscle is inferred.