The role of Ca2+ in stimulated bioluminescence of the dinoflagellateLingulodinium polyedrum

Many marine dinoflagellates emit bright discrete flashes of light nearly instantaneously in response to either laminar or turbulent flows as well as to direct mechanical stimulation. The flash involves a unique pH-dependent luciferase and a proton-mediated action potential across the vacuole membrane. The mechanotransduction process initiating this action potential is unknown. The present study investigated the role of Ca(2+) in the mechanotransduction process regulating bioluminescence in the dinoflagellate Lingulodinium polyedrum. Calcium ionophores and digitonin stimulated luminescence in a Ca(2+)-dependent manner in the absence of mechanical stimulation. Mechanically sensitive luminescence was strongly inhibited by the intracellular Ca(2+) chelator BAPTA-AM [1,2-bis(o-aminophenoxy)ethane-N,N,N',N'- tetraacetic acid acetoxymethyl ester]; there was only a partial and irreversible dependence on extracellular Ca(2+). Ruthenium Red, a blocker of intracellular Ca(2+) release channels, inhibited mechanically sensitive luminescence. Luminescence was also stimulated by increasing K(+), even in the absence of extracellular Ca(2+); K(+) stimulation was inhibited both by BAPTA-AM and Ruthenium Red. These results support the hypothesis that Ca(2+) mediates stimulated bioluminescence and also indicate the involvement of intracellular Ca(2+) stores. Rapid coupling between mechanical stimulation and mobilization of intracellular Ca(2+) stores might occur through a mechanism similar to excitation-contraction coupling in skeletal muscle.