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Single-Cell Calcium Imaging for Studying the Activation of Calcium Ion Channels
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[Direct evidences of calcium traffic through pacemaker channel]
Rossiiskii Fiziologicheskii Zhurnal Imeni I.M. Sechenova
|December 2, 2014
Summary
Calcium ions can pass through pacemaker HCN2 channels, a finding demonstrated in both hamster cells and rat heart cells. This calcium permeability is regulated by cyclic adenosine monophosphate and blocked by ivabradine.
Area of Science:
- Cardiology
- Molecular Biology
- Ion Channel Physiology
Background:
- Pacemaker hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are crucial for heart rhythm.
- Previous research suggested HCN channels conduct Na+ and K+ ions.
- Emerging evidence indicated potential permeability to other ions, including calcium.
Purpose of the Study:
- To investigate the permeability of pacemaker HCN2 channels to calcium ions.
- To characterize the properties of calcium currents through HCN2 channels.
- To confirm calcium ion conduction in native f-channels.
Main Methods:
- Expression of HCN2 channel in Chinese hamster ovarian cells.
- Patch-clamp electrophysiology to measure ionic currents.
- Application of cyclic adenosine monophosphate (cAMP) and ivabradine to modulate channel activity.
- Electrophysiological recordings from neonatal rat ventricular cells.
Main Results:
- A low-amplitude calcium current (0.06±-0.87 nA) was measured through expressed HCN2 channels.
- The calcium current exhibited a low open probability (0.48%) at -110 mV.
- Cyclic adenosine monophosphate significantly increased HCN2-Ca2+ current open probability.
- The specific If-blocker ivabradine inhibited the measured calcium current.
- Calcium ion current was also observed in native f-channels of rat ventriculocytes.
Conclusions:
- Pacemaker HCN2 channels are permeable to calcium ions.
- Calcium ion conduction through HCN2 channels is regulated by cAMP and blocked by ivabradine.
- Demonstrated physiological relevance of calcium ion conduction through HCN2 and native f-channels in cardiomyocytes.
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