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The hyperpolarisation-activated current, I(f), is not required for pacemaking in single cells from the rabbit
Pflugers Archiv : European Journal of Physiology
|May 1, 1994
Summary
The majority of rabbit atrioventricular node (AVN) cells generate pacemaker activity without the hyperpolarisation-activated inward current (I(f)). This suggests I(f) channels may be absent in most AVN cells, challenging previous assumptions about cardiac pacemaking.
Area of Science:
- Cardiology
- Electrophysiology
- Cell Biology
Background:
- The atrioventricular node (AVN) is crucial for maintaining cardiac rhythm.
- The hyperpolarisation-activated inward current (I(f)) is a known contributor to pacemaker activity.
Purpose of the Study:
- To investigate the role of I(f) in generating pacemaker activity in rabbit AVN cells.
- To determine if I(f) is essential for normal pacemaker function in the AVN.
Main Methods:
- Whole-cell patch-clamp recordings were used on isolated rabbit AVN myocytes.
- The effects of isoprenaline and manganese on I(f) and action potential rate were assessed.
Main Results:
- 80%-90% of AVN cells (type 1) generated action potentials without detectable I(f).
- A small subset of AVN cells (type 2) exhibited I(f), which was modulated by isoprenaline and manganese.
- Isoprenaline increased the action potential rate in type 1 cells without activating I(f).
Conclusions:
- Pacemaker depolarization in the majority of AVN cells occurs independently of I(f).
- I(f) channels may be absent in most AVN cells, suggesting alternative mechanisms for pacemaking.
- I(f) likely plays a modulatory role in the smaller population of AVN cells that possess it.