C terminus-mediated control of voltage and cAMP gating of hyperpolarization-activated cyclic nucleotide-gated channels.
The hyperpolarization-activated cyclic nucleotide-gated (HCN) family of "pacemaker" channels includes 4 isoforms, the kinetics and cAMP-induced modulation of which differ quantitatively. Because HCN isoforms are highly homologous in the central region, but diverge more substantially in the N and C termini, we asked whether these latter regions could contribute to the determination of channel properties. To this aim, we analyzed activation/deactivation kinetics and the response to cAMP of heterologously expressed isoforms mHCN1 and rbHCN4 and verified that mHCN1 has much faster kinetics and lower cAMP sensitivity than rbHCN4. We then constructed rbHCN4 chimeras by replacing either the N or the C terminus, or both, with the analogous domains from mHCN1. We found that: 1) replacement of the N terminus (chimera N1-4) did not substantially modify either the kinetics or cAMP dependence of wild-type channels; 2) replacement of the C terminus, on the contrary, resulted in a chimeric channel (4-C1), the kinetics of which were strongly accelerated compared with rbHCN4, and that was fully insensitive to cAMP; 3) replacement of both N and C termini led to the same results as replacement of the C terminus alone. These results indicate that the C terminus of rbHCN4 contributes to the regulation of voltage- and cAMP-dependent channel gating, possibly through interaction with other intracellular regions not belonging to the N terminus.
Viscomi
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Dipartimento di Fisiologia e Biochimica Generali, Laboratorio Fisiologia Molecolare e Neurobiologia, and INFM, Unità Milano Università, via Celoria 26, 20133 Milano, Italy.
Altomare
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Bucchi
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Camatini
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Baruscotti
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Moroni
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DiFrancesco
D
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D000818:Animals; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism*; D054815:Cyclic Nucleotide-Gated Cation Channels; D004594:Electrophysiology; D049452:Green Fluorescent Proteins; D006801:Humans; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D007700:Kinetics; D008164:Luminescent Proteins / Q000378:metabolism; D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014162:Transfection
D054815:Cyclic Nucleotide-Gated Cation Channels; C119587:HCN4 protein, human; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels; D008164:Luminescent Proteins; D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D000242:Cyclic AMP