Activity-Dependent Regulation of Ether á … go-go K+ Channels.

[摘要] The Drosophila ether á go-go (eag) gene encodes a partially inactivating, voltage-gated K+ channel expressed at neuromuscular and CNS synapses. Recordings from the larval neuromuscular junctions (NMJs) of eag mutants, compared to wild type, reveal a high level of spontaneous activity in the motor nerve and broader evoked excitatory junctional potentials.Also, EAG is one of the few K+ channels that demonstrate a role in learning and memory as assayed by habituation and courtship conditioning protocols.The goals of my thesis are to better understand the mechanisms by which neuronal activity affects EAG function and how EAG channels contribute to neuronal function.Since neuronal activity changes Ca2+ concentrations within the cell, I focused on how Ca2+-dependent mechanisms could regulate EAG channels.Proteins that modulate EAG current include calmodulin (CaM), the calcium (Ca2+)/calmodulin (CaM)-dependent protein kinase II (CaMKII) and the Camguk/CASK (CMG) adaptor protein.Phosphorylation of EAG by CaMKII and association with CMG produce relatively long-term effects by regulating EAG surface expression, whereas CaM binding acutely down-regulates EAG current.In addition, EAG channels regulate CaMKII activity by a mechanism not dependent on ion conduction, but rather, depends on conformational changes associated with the position of the voltage sensor.The temporal difference in the regulation of EAG by increased intracellular Ca2+ suggests a model in which CaM binding affects short-term plasticity, whereas CaMKII and CMG regulation of EAG affect more long-term, homeostatic adjustments to increased neuronal activity.In vivo, signaling deficient channels fail to rescue high levels of spontaneous activity characteristic of eag mutants, suggesting that voltage-dependent, conductance-independent EAG signaling plays a role in the homeostatic regulation of neuronal activity.These results identify, until now, an unknown function for voltage sensing of EAG and suggest this mechanism may serve as a direct link between neuronal activity and the state of intracellular messengers.Transgenic expression of EAG channels that cannot bind CaM or be phosphorylated by CaMKII show Ca2+/CaM and CaMKII independently modulate EAG currents. Inhibition of EAG by CaM binding is necessary for facilitation at the larval NMJ, and phosphorylation of EAG at its CaMKII site is essential for proper synaptic function.

[发布机构] University of Michigan

[效力级别] Drosophila

[关键词] Potassium Channel;Drosophila;Synapse;Calcium;Molecular;Cellular and Developmental Biology;Health Sciences;Molecular, Cellular, and Developmental Biology