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Correlation between electrical activity and the size of rabbit sino-atrial node cells
H Honjo1, M R Boyett, I Kodama
1Department of Circulation, Nagoya University, Japan. honjo@riem.nagoya-u.ac.jp
The Journal of Physiology
|November 1, 1996
Summary
Larger rabbit sino-atrial node cells exhibit faster spontaneous activity and greater electrical signal properties due to increased hyperpolarization-activated current (i(f)) and TTX-sensitive sodium current (iNa). This indicates electrophysiological heterogeneity within the SA node.
Area of Science:
- Cardiovascular Physiology
- Electrophysiology
- Cell Biology
Background:
- The sino-atrial (SA) node is the primary pacemaker of the heart.
- Understanding the electrophysiological properties of SA node cells is crucial for comprehending cardiac rhythm regulation.
Purpose of the Study:
- To investigate the relationship between the size of rabbit SA node cells and their electrical activity.
- To determine how cell size influences membrane currents and action potential characteristics.
Main Methods:
- Single SA node cells were isolated from rabbits using enzymatic dissociation.
- Whole-cell patch clamp technique was employed to record spontaneous action potentials and membrane currents.
- Cell capacitance was measured to estimate cell size.
Main Results:
- Larger SA node cells demonstrated increased action potential amplitude, faster upstroke velocity, and a higher rate of diastolic depolarization.
- The density of hyperpolarization-activated current (i(f)) and TTX-sensitive sodium current (iNa) was greater in larger cells.
- TTX-sensitive sodium current (iNa) was absent in smaller cells (capacitance < 25 pF).
Conclusions:
- Rabbit SA node cells are electrophysiologically heterogeneous, with size correlating to electrical properties.
- Differences in i(f) and iNa densities contribute to the faster spontaneous activity observed in larger SA node cells.
- Cell size is a key determinant of electrical membrane properties in SA node pacemaker cells.