Excitation-Contraction Coupling in Barnacle Muscle Fibers: Does Calcium Entry Trigger Contraction Directly?

Abstract

It is well known that mechanical activation of muscle from both vertebrates and invertebrates is triggered by an elevation of the concentration of free-calcium in the sarcoplasm. In skeletal muscle fibers from vertebrates this ion is actively transported into the sarcoplasmic reticulum (SR) and released at the level of the terminal cisternae of the SR following the regenerative depolarization of the transverse tubular membrane.(1)) However, the question of the origin of the calcium required for mechanical activation in invertebrate skeletal muscle has not been yet elucidated. (2)