FUNCTIONAL EXPRESSION OF SHAKER K-NEURONS DERIVED FROM SH CDNA TRANSFORMANTS - DISTINCT PROPERTIES, DISTRIBUTION, AND TURNOVER( CHANNELS INCULTURED DROSOPHILA GIANT)
Ml. Zhao et al., FUNCTIONAL EXPRESSION OF SHAKER K-NEURONS DERIVED FROM SH CDNA TRANSFORMANTS - DISTINCT PROPERTIES, DISTRIBUTION, AND TURNOVER( CHANNELS INCULTURED DROSOPHILA GIANT), The Journal of neuroscience, 15(2), 1995, pp. 1406-1418
Expression of transgenic Shaker (Sh) channels has not previously been
examined in Drosophila neurons. We studied K+ current by whole-cell re
cording in cultured ''giant'' neurons derived from germline transforma
nts. 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)-i
nducible promoter. Transformants in wildtype and two different Sh muta
nt backgrounds all exhibited an HS-inducible, A-type K+ current that w
as characterized by a much slower recovery from inactivation and a hig
her sensitivity to 4-aminopyridine than native K+ currents or Sh 29-4
currents expressed in Xenopus oocytes. Despite similarities in the kin
etic and pharmacological properties of the HS-induced current in all b
ackgrounds examined, host-dependent differences in the peak current am
plitude have been consistently observed between multiple lines of 29-4
Sh(M) and 29-4 Sh(120) that might reflect differential channel subuni
t assembly in different hosts. Isolation of the novel 29-4 currents al
lowed determination of the channel turnover rate in cultured neurons.
These currents persisted for up to 3 d or more, comparable with the du
rations previously reported for Na+ and Ca2+ channels. Surprisingly, t
he percentage of cells expressing inactivating K+ currents remained ap
proximately the same with or without HS induction, suggesting that som
e mechanisms exist to restrict functional expression of inactivating K
+ channels, including transgenic Sh channels and those trot encoded by
the Sh locus, to certain types of neurons.