VON DASSOW, Peter: Calcium mediated mechanotransduction in flow-stimulated bioluminescence of dinoflagellates

Many marine dinoflagellates emit bright discrete flashes of light nearly instantaneously in response to either laminar or turbulent flows as well as direct mechanical stimulation. This response is believed to function to deter consumption by planktivorous animals. The flash involves a unique pH-dependent luciferase and a proton-mediated action potential across the vacuole membrane. The mechanotranduction process initiating this action potential is unknown. Using two flow systems, including developing laminar Couette flow, I investigated the role of Ca²⁺ in the mechanotransduction process regulating bioluminescence in the red tide dinoflagellate Lingulodinium polyedrum. Calcium ionophores and digitonin stimulated bioluminescence in a calcium-dependent manner in the absence of mechanical stimulation. The intracellular Ca²⁺ chelator BAPTA-AM strongly inhibited mechanically sensitive bioluminescence. Gadolinium, a blocker of many stretch-activated ion channels, and several other known Ca²⁺ channel blockers rapidly inhibited mechanical stimulation of bioluminescence but did not reduce luminescent capacity. In contrast to previously reported results, there was only a weak and irreversible dependence on extracellular calcium for mechanical sensitivity. Ruthenium red, a blocker of intracellular calcium release channels, strongly inhibited mechanical sensitivity. These results indicate the involvement of both plasma membrane channels and intracellular Ca²⁺ stores in the coupling between the plasma membrane and the vacuole membrane, which might be similar to excitation-contraction coupling in skeletal muscle.