title: Hyperpolarization-activated cyclic nucleotide-gated channels in pancreatic beta-cells.
abstract: Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels mediate the pacemaker current (Ih or If) observed in electrically rhythmic cardiac and neuronal cells. Here we describe a hyperpolarization-activated time-dependent cationic current, beta-Ih, in pancreatic beta-cells. Transcripts for HCN1-4 were detected by RT-PCR and quantitative PCR in rat islets and MIN6 mouse insulinoma cells. beta-Ih in rat beta-cells and MIN6 cells displayed biophysical and pharmacological properties similar to those of HCN currents in cardiac and neuronal cells. Stimulation of cAMP production with forskolin/3-isobutyl-1-methylxanthine (50 microM) or dibutyryl-cAMP (1 mM) caused a significant rightward shift in the midpoint activation potential of beta-Ih, whereas expression of either specific small interfering (si)RNA against HCN2 (siHCN2b) or a dominant-negative HCN channel (HCN1-AAA) caused a near-complete inhibition of time-dependent beta-Ih. However, expression of siHCN2b in MIN6 cells had no affect on glucose-stimulated insulin secretion under normal or cAMP-stimulated conditions. Blocking beta-Ih in intact rat islets also did not affect membrane potential behavior at basal glucose concentrations. Taken together, our experiments provide the first evidence for functional expression of HCN channels in the pancreatic beta-cell.
authors.affiliation: Department of Medicine, University of Toronto, Toronto, Canada M5S 1A8.
authors.forename: Wasim
authors.initials: W
authors.lastname: El-Kholy
authors.forename: Patrick E
authors.initials: PE
authors.lastname: MacDonald
authors.forename: Jocelyn Manning
authors.initials: JM
authors.lastname: Fox
authors.forename: Alpana
authors.initials: A
authors.lastname: Bhattacharjee
authors.forename: Tian
authors.initials: T
authors.lastname: Xue
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Gao
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.forename: Juliane
authors.initials: J
authors.lastname: Stieber
authors.forename: Ronald A
authors.initials: RA
authors.lastname: Li
authors.forename: Robert G
authors.initials: RG
authors.lastname: Tsushima
authors.forename: Michael B
authors.initials: MB
authors.lastname: Wheeler
mesh_terms: D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000502:physiology; D054815:Cyclic Nucleotide-Gated Cation Channels; D004594:Electrophysiology; D005089:Exocytosis / Q000187:drug effects; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D007340:Insulinoma / Q000473:pathology; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D010880:Piperidines / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats
chemical_list: D001552:Benzazepines; D054815:Cyclic Nucleotide-Gated Cation Channels; C578666:Hcn1 protein, mouse; C578667:Hcn1 protein, rat; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007328:Insulin; D010880:Piperidines; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D011743:Pyrimidines; D034741:RNA, Small Interfering; C082246:ICI D2788; C490484:cilobradine; D000242:Cyclic AMP