Modulation of reconstituted ATP-sensitive K+ channels by GTP-binding proteins in a mammalian cell line

摘要

The action of GTP-binding proteins on ATP-sensitive potassium (KATP) channels was investigated. KATP channels were expressed in a mammalian cell line (COS-1 cells) by cotransfecting vectors carrying the sulphonylurea receptor (SUR1) and BIR (Kir6.2), a member of the inward rectifier K+ channel family. G proteins were also tested on KATP channels composed of an isoform of SUR1, SUR2A, in combination with Kir6.2.The α and βγ subunits of the GTP binding protein Gi were tested separately in inside-out patches under continuous recording. Gα-i1 increases the activity of SUR1-Kir6.2 and SUR2A-Kir6.2 channels by 200 and by 30 %, respectively.Gα-i2 does not increase the activity of SUR1-Kir6.2 channels, but increases the activity of SUR2A-Kir6.2 channels by 30 %.Control experiments showed that GTPγS, a specific activator of G proteins, and heat- inactivated Gα-i1 do not increase the single channel activity.No effects of the other subunits (βγ) from either Gi1 or Gi2 on the single channel activity were observed.The protein kinase C inhibitors H7 and an inhibitory peptide (FARKGALRQKNV) had no effect on the modulatory action of Gα-i1 on SUR1-Kir6.2 channels.We conclude that both types of reconstituted KATP channels are modulated by G proteins.