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GPCRs are primarily responsible for our sense of smell, taste, and vision. The binding of a sensory stimulus activates GPCR to stimulate effector proteins, many of which are ion channels in the sensory organs. GPCRs modulate the opening and closing of the target ion channels either directly by binding them, or by releasing second messengers that activate these channels. As ions move across the membrane, the membrane potential is altered, which induces an appropriate response.
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Voltage-gated Ion Channels

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Mechanically-gated Ion Channels

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Mechanically-gated ion channels are proteins found in eukaryotic and prokaryotic cell membranes that open in response to mechanical stress. Tension, compression, swelling, and shear stress can alter the conformation of the protein, opening a transmembrane channel that allows the passage of ions for signal transmission. In eukaryotes, mechanically-gated channels are distributed in several regions like the neurons, lungs, skin, bladder, and heart, where they play critical roles in numerous...

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Related Experiment Video

Updated: Jul 4, 2025

Voltage-Dependent Potassium Current Recording on H9c2 Cardiomyocytes via the Whole-Cell Patch-Clamp Technique

Voltage-Dependent Potassium Current Recording on H9c2 Cardiomyocytes via the Whole-Cell Patch-Clamp Technique

Published on: November 11, 2022

A high affinity switch for cAMP in the HCN pacemaker channels.

Alessandro Porro¹, Andrea Saponaro², Roberta Castelli¹

¹Department of Biosciences, University of Milan, Milano, Italy.

Nature Communications

|January 29, 2024

Summary

Hyperpolarization activated cyclic nucleotide gated (HCN) channels possess an affinity switch for cAMP. Alpha helices D and E stabilize the cyclic nucleotide binding domain, significantly increasing cAMP binding affinity and efficacy.

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Last Updated: Jul 4, 2025

Voltage-Dependent Potassium Current Recording on H9c2 Cardiomyocytes via the Whole-Cell Patch-Clamp Technique

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Published on: November 11, 2022

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Published on: November 11, 2016

Recapitulation of an Ion Channel IV Curve Using Frequency Components

Recapitulation of an Ion Channel IV Curve Using Frequency Components

Published on: February 8, 2011

Area of Science:

Molecular biology
Biophysics
Neuroscience

Background:

Hyperpolarization activated cyclic nucleotide gated (HCN) channels are crucial for neuronal excitability.
cAMP binding to the cyclic nucleotide binding domain (CNBD) regulates HCN channel activity.
The lower in vitro cAMP affinity of the isolated CNBD compared to full-length channels remains unexplained.

Purpose of the Study:

To elucidate the mechanism behind the higher cAMP affinity of full-length HCN channels compared to the isolated CNBD.
To identify the structural elements responsible for modulating cAMP binding affinity in HCN channels.

Main Methods:

Patch clamp electrophysiology to measure cAMP-dependent channel activity.
Isothermal Titration Calorimetry (ITC) to quantify binding affinity.
Structural analysis of the HCN channel cyclic nucleotide binding domain (CNBD) and associated helices.

Main Results:

HCN channels exhibit an intrinsic "affinity switch" for cAMP.
Alpha helices D and E, located downstream of the CNBD, stabilize the holo CNBD in a high-affinity state.
These helices enhance cAMP efficacy by 30-fold (patch clamp) and affinity (ITC).
Helices D and E interact with helix C of the CNBD, mimicking regulation by TRIP8b.

Conclusions:

An intramolecular mechanism involving helices D and E regulates HCN channel activity by modulating cAMP binding affinity.
This mechanism provides a novel layer of HCN channel regulation, independent of cAMP concentration.
Understanding this affinity switch is critical for comprehending HCN channel function in physiological and pathological conditions.