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K(+) current distribution in rat sub-epicardial ventricular myocytes
Kimiaki Komukai1, Fabien Brette, Tomoko T Yamanushi
1School of Biomedical Sciences, University of Leeds, Leeds LS2 9NQ, UK.
Pflugers Archiv : European Journal of Physiology
|July 24, 2002
Summary
Transient outward potassium current (I(TO)) is uniformly distributed in rat ventricular cells. This finding clarifies the functional distribution of I(TO) and other ion currents between the cell surface and t-tubules.
Area of Science:
- Cardiovascular Physiology
- Molecular Cardiology
- Ion Channel Biophysics
Background:
- The transient outward potassium current (I(TO)) in the rat ventricle is crucial for action potential repolarization.
- I(TO) is primarily carried by heteromeric channels composed of Kv4.2 and Kv4.3 subunits.
- The precise localization of I(TO) channels within cardiac ventricular cells, specifically between the sarcolemma and t-tubules, remains poorly understood.
Purpose of the Study:
- To investigate the functional distribution of the transient outward potassium current (I(TO)) in rat ventricular myocytes.
- To determine whether I(TO) is uniformly distributed across the cell surface membrane and transverse tubules (t-tubules).
- To compare the distribution of I(TO) with other potassium currents (I(K), I(K1), I(SS)) and the L-type calcium current (I(Ca)).
Main Methods:
- Utilized the patch-clamp technique on isolated rat ventricular myocytes.
- Employed formamide treatment to selectively detubulate cardiac cells, differentiating between surface membrane and t-tubule contributions.
- Monitored various potassium currents (I(TO), I(K), I(K1), I(SS)) and L-type calcium current (I(Ca)) in control and detubulated cells.
Main Results:
- Detubulation reduced cell capacitance by 20% but did not significantly alter the density of I(TO), I(K), or I(K1).
- The density of the steady-state potassium current (I(SS)) and L-type calcium current (I(Ca)) was significantly decreased in detubulated cells.
- These findings indicate a uniform distribution of I(TO), I(K), and I(K1) between the sarcolemma and t-tubules.
Conclusions:
- The transient outward potassium current (I(TO)), along with the delayed rectifier (I(K)) and inward rectifier (I(K1)) potassium currents, are functionally distributed uniformly across the surface and t-tubule membranes in rat ventricular cells.
- The steady-state potassium current (I(SS)) and L-type calcium current (I(Ca)) are predominantly localized to the t-tubules.
- This differential distribution has significant implications for understanding cardiac electrophysiology and action potential dynamics.