title: Functional expression of Shaker K+ channels in cultured Drosophila "giant" neurons derived from Sh cDNA transformants: distinct properties, distribution, and turnover.
abstract: Expression of transgenic Shaker (Sh) channels has not previously been examined in Drosophila neurons. We studied K+ current by whole-cell recording in cultured "giant" neurons derived from germline transformants. Independent lines were generated by using a P-element vector, in which transcription of the 29-4 cDNA, one of the Sh splicing variants (Iverson and Rudy, 1990), was under the control of a heat shock (HS)-inducible promoter. Transformants in wild-type and two different Sh mutant backgrounds all exhibited an HS-inducible, A-type K+ current that was characterized by a much slower recovery from inactivation and a higher sensitivity to 4-aminopyridine than native K+ currents of Sh 29-4 currents expressed in Xenopus oocytes. Despite similarities in the kinetic and pharmacological properties of the HS-induced current in all backgrounds examined, host-dependent differences in the peak current amplitude have been consistently observed between multiple lines of 29-4 ShM and 29-4 Sh120 that might reflect differential channel subunit assembly in different hosts. Isolation of the novel 29-4 currents allowed determination of the channel turnover rate in cultured neurons. These currents persisted for up to 3 d or more, comparable with the durations previously reported for Na+ and Ca2+ channels. Surprisingly, the percentage of cells expressing inactivating K+ currents remained approximately the same with or without HS induction, suggesting that some mechanisms exist to restrict functional expression of inactivating K+ channels, including transgenic Sh channels and those not encoded by the Sh locus, to certain types of neurons.
authors.affiliation: Department of Biological Sciences, University of Iowa, Iowa City 52242.
authors.forename: M L
authors.initials: ML
authors.lastname: Zhao
authors.forename: E O
authors.initials: EO
authors.lastname: Sable
authors.forename: L E
authors.initials: LE
authors.lastname: Iverson
authors.forename: C F
authors.initials: CF
authors.lastname: Wu
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D002478:Cells, Cultured; D018076:DNA, Complementary / Q000235:genetics; D004330:Drosophila / Q000235:genetics* / Q000378:metabolism*; D004553:Electric Conductivity; D006358:Hot Temperature; D007700:Kinetics; D015335:Molecular Probes / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D012769:Shock / Q000503:physiopathology; D013997:Time Factors; D014018:Tissue Distribution
chemical_list: D018076:DNA, Complementary; D015335:Molecular Probes; D015221:Potassium Channels; D015761:4-Aminopyridine