Ca²⁺-signal transduction in photoreceptor synapses

In this project Ca²⁺-dependent signalling mechanisms in the photoreceptor synapse will be analyzed. Photoreceptor synapses are ribbon-type synapses, specialized chemical synapses that are optimized to transmit sensory informations over a broad bandwidth of stimulus intensities. Fusion of synaptic vesicles with the presynaptic plasma membrane is initiated and regulated by Ca²⁺-influx through voltage-gated Ca²⁺-channels.

The ribbon synapse performs both fast, phasic exocytosis as well as slower, tonic vesicle exocytosis which can be maintained for prolonged periods of time. The high rate of vesicle exocytosis in ribbon synapses needs to matched by compensatory vesicle endocytosis to prevent synaptic fatiguing. Furthermore, in photoreceptor ribbon synapses the synaptic machinery needs to be adjusted to different levels of activity during light/dark adaptation.

The described processes are dependent on presynaptic Ca²⁺ although the molecular details are largely unknown. The molecular and functional characterization of these Ca²⁺-dependent pathways in photoreceptor synapses is the main goal of the research proposal.