title: Drosophila QVR/SSS modulates the activation and C-type inactivation kinetics of Shaker K(+) channels.
abstract: The quiver/sleepless (qvr/sss) gene encodes a small, glycosylphosphatidylinositol-anchored protein that plays a critical role in the regulation of sleep in Drosophila. Loss-of-function mutations in qvr/sss severely suppress sleep and effect multiple changes in in situ Shaker K(+) currents, including decreased magnitude, slower time-to-peak, and cumulative inactivation. Recently, we demonstrated that SLEEPLESS (SSS) protein modulates Shaker channel activity, possibly through a direct interaction at the plasma membrane. We show here that SSS accelerates the activation of heterologously expressed Shaker channels with no effect on deactivation or fast N-type inactivation. Furthermore, this SSS-induced acceleration is sensitive to the pharmacological disruption of lipid rafts and sufficiently accounts for the slower time-to-peak of in situ Shaker currents seen in qvr/sss mutants. We also find that SSS decreases the rate of C-type inactivation of heterologously expressed Shaker channels, providing a potential mechanism for the cumulative inactivation phenotype induced by qvr/sss loss-of-function mutations. Kinetic modeling based on the in vitro results suggests that the SSS-dependent regulation of channel kinetics accounts for nearly 40% of the decrease in Shaker current magnitude in flies lacking SSS. Sleep duration in qvr/sss-null mutants is restored to normal by a qvr/sss transgene that fully rescues the Shaker kinetic phenotypes but only partially rescues the decrease in current magnitude. Together, these results suggest that the role of SSS in the regulation of sleep in Drosophila correlates more strongly with the effects of SSS on Shaker kinetics than current magnitude.
authors.affiliation: Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Terry
authors.initials: T
authors.lastname: Dean
authors.forename: Rong
authors.initials: R
authors.lastname: Xu
authors.forename: William
authors.initials: W
authors.lastname: Joiner
authors.forename: Amita
authors.initials: A
authors.lastname: Sehgal
authors.forename: Toshinori
authors.initials: T
authors.lastname: Hoshi
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001703:Biophysics; D002461:Cell Line, Transformed; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004558:Electric Stimulation / Q000379:methods; D006801:Humans; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000235:genetics; D007700:Kinetics; D021962:Membrane Microdomains / Q000378:metabolism; D008564:Membrane Potentials / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009132:Muscles / Q000502:physiology; D009154:Mutation / Q000235:genetics; D018408:Patch-Clamp Techniques; D051637:Shaker Superfamily of Potassium Channels / Q000235:genetics / Q000378:metabolism*; D007319:Sleep Initiation and Maintenance Disorders / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D029721:Drosophila Proteins; D008565:Membrane Proteins; C530371:Qvr protein, Drosophila; C496929:Sh protein, Drosophila; D051637:Shaker Superfamily of Potassium Channels