On the relationships between membrane potential, calcium transient and tension in single barnacle muscle fibres

The calcium-sensitive photoprotein aequorin has been used to follow the rapid changes in intracellular calcium concentration that occur during the contraction of single muscle fibres from the barnacle Balanus nubilus, Darwin.2. The transient change in calcium-mediated light emission (calcium transient) and the changes in membrane potential and tension were recorded simultaneously, thus permitting an examination of the relationships between the chemical, electrical, and mechanical events of excitation-contraction coupling.3. With short-duration stimuli ( 250-300 msec), the calcium transient falls slowly from its maximum value despite continued membrane depolarization, suggesting a time-dependent change in the ratio of the rate of release of calcium to the rate of calcium binding. The results from brief tetanic stimulation also support this suggestion.