Electrophysiological, pharmacological and behavioural characterisation of the Drosophila KCNQ channel

• Main Author: Cavaliere, Sonia
• Published: University of Bristol 2011
• Subjects: 595.774
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.555722

There are five KCNQ (Kv7) channels in humans. The cardiac KCNQl channel when assembled with KCNEl mediates the cardiac IKs current with mutations causing short and long QT cardiac arrhythmias. Neuronal KCNQ2/3 channels form the M-current that controls excitability of most neurons with mutations causing a form of epilepsy called benign neonatal familial convulsions. KCNQ4 mutations cause deafuess and age dependent hearing loss. KCNQ5 is expressed in the hippocampus and cortex and is also thought to regulate excitability and plasticity in these brain regions. Drosophila has a single KCNQ channel (dKCNQ) that shares roughly 50-60% amino acid identity with mammalian KCNQ channels. dKCNQ is expressed in Drosophila neurons and heart and is thought to encode an M-current in neurons. In the heart mutations dKCNQ has previously been shown to cause age-dependent arrhythmias. In order to further validate Drosophila as a model to study KCNQ function and channelopathies, it has been performed for the first time a comparison of the physiological and pharmacological properties of dKCNQ with respect to the mammalian neuronal and cardiac KCNQ channels expressed in HEK cells. dKCNQ shares similar electrophysiological properties with mammalian KCNQs, being most similar to the neuronal KCNQ2/3 but having some features on the cardiac KCNQIIKCNEl channel. Furthermore, dKCNQ shows conserved pharmacology with the mammalian KCNQ channels including sensitivity to KCNQ blockers (chromanol 293B, XE991, linopirdine) and openers such as retigabine and zinc pyrithione. Finally was showed that dKCNQ and mammalian KCNQ2/3 display conserved sensitivity to acute low doses of ethanol. Subsequently was described for the first time the role of KCNQ in the Drosophila nervous system. Deletion mutations of dKCNQ result in ethanol hypersensitivity, a behavioural phenotype that maps to dopamine and serotonin neurons, neurotransmitter systems. In addition was identified that the dKCNQ mutant shows increased ethanol tolerance phenotype. Data is also presented showing that over-expression and knock-down of dKCNQ in Drosophila neurons results in a bi- directional change in neural excitability and disruption of neural release in dopamine and serotonin neurons. Furthermore, KCNQ mutants display decrements in associative learning with a role of dKCNQ in the mushroom body, amnesiac and associated learning neurons. It was demonstrated that after ethanol-exposure, wild-type flies have disrupted learning an effect removed by dKCNQ deletion mutants, suggesting that dKCNQ is a direct target of ethanol. Lastly, was showed that wild-type flies show memory impairment when they get old an effect mimicked by KCNQ mutations with young and old dKCNQ mutants having similar levels of impairment as aged wild-type flies. Aged wild-type flies display an 80-90% reduction in dKCNQ compared to young flies. This study characterises for the first time the in vivo consequence of loss of function and over-expression of dKCNQ on neuronal function and behaviour showing a role in ethanol sensitivity and tolerance as well as learning and memory. Therefore the single Drosophila KCNQ channel shows conserved and intermediate electrophysiological and pharmacology properties between the mammalian brain and cardiac KCNQ channels, with similar functions in these tissues in the whole animal, validating the future use of Drosophila as a genetic model of KCNQ function and channelopathies.