Dr Tsien's lab is studying how the location and identity of presynaptic calcium channels is regulated. Voltage-gated Ca2+ channels provide the critical link between the firing of a presynaptic nerve terminal and its release of neurotransmitter. The Ca2+ channels must be positioned very close to sites of vesicle fusion, and come in diverse forms with distinct activity-dependence, responsiveness to GABA, dopamine, acetylcholine and other neuromodulators, and susceptibility to neurological disorders such as migraine, ataxia or dystonia. Our working hypothesis involves molecular "slots" for particular types of channels. Slots regulate the mix of channel types and also help explain how defective channels might displace normal ones in genetically dominant disorders.