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Media type:
E-Book;
Thesis
Title:
Role of individual subunits in Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channel gating
Parallel title:
Die Rolle der einzelnen Untereinheiten beim Schalten des durch Hyperpolarisation aktivierten und durch zyklische Nucleotide modulierten (HCN) Kanals
University thesis:
Dissertation, Friedrich-Schiller-Universität Jena, 2019
Footnote:
Tag der Verteidigung: 22.10.2019
Zusammenfassungen in deutscher und englischer Sprache
Description:
Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels are tetramers that elicit electrical rhythmicity in special brain neurons and cardiomyocytes. These channels are non-selective cationic channels which are activated by hyperpolarizing voltages and modulated by the binding of adenosine 3’, 5’ -cyclic monophosphate (cAMP) to the four cyclic nucleotidebinding domains (CNBD). The binding of cAMP shifts steady-state activation to more positive voltages, thereby accelerating the activation and increasing the current along with a slowing effect on deactivation. Inspite of knowing the structure of the isolated CNBDs by crystals and X-ray analysis and very recent insights into the HCN1 structure by cryo-electron microscopy, many questions on the function of these channels remain open. In particular, how the successive binding of four cyclic nucleotides is transmitted to change the operation of the channels and how the two stimuli,hyperpolarization and cAMP binding, are interlinked. So, the aim of this work was to study the role of individual subunits in the ligand (cAMP)-dependent activation and deactivation process of HCN2 channels with the help of patch-clamp technique and Xenopus laevis oocytes as an expression system. This project was focused to analyze the effects of cAMP binding to the subunits of HCN2 concatameric channels with a defined number of functional CNBDs. It was found that each liganded CNBD promotes channel activation in an additive manner irrespective of their position within the tetramer. In contrast, the open probability reached its maximum already when only two subunits were liganded. However, the process of deactivation was differently influenced by cAMP binding. Liganding of four, three, or at least two CNBDs in trans position slowed the deactivation process, whereas channels with either two functional CNBDs in cis position or with a single functional subunit were ineffective to decelerate the deactivation process. Together the results showed herein support an activation mechanism in which each single liganded CNBD (out of four) supports channel opening by causing a turning momentum on the tetrameric intracellular gating ring, thereby stabilizing the open pore. For maintaining activation, however, at least two subunits in trans position are needed to be liganded.