Kinetic investigations in single muscle fibres using luminescent and fluorescent Ca 2+ probes

Abstract

The Ca 2+-sensitive photoprotein aequorin and the Ca 2+-dependent fluorescent indicators quin 2 and TnCDANZ have been used to investigate contractile processes in single crustacean muscle fibres. The investigations with quin 2 indicate that the free Ca 2+ rises to a maximum value before peak force as with aequorin light (∼ 200 msec delay at 12°C) and subsequently decays more slowly, unlike the majority of the aequorin signal, although an aequorin ‘tail’ signal remains. The resting quin 2 fluorescence from the cell suggests an upper limit of 348 nM for the resting calcium concentration. Experiments with TnCDANZ indicate that this fluorescence response rises rapidly but then the rate of rise slows to reach a maximum value at a time when peak force is achieved and then the fluorescence signal decays more slowly than force. The latter result implies that Ca 2+ is attached to the Ca 2+-specific sites of TnC when externally recorded force is small.