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Cardiac Purkinje fibers: cesium as a tool to block inward rectifying potassium currents
Abstract:
When a cardiac Purkinje fiber is exposed to 20 mM Cs the membrane potential falls to about -60 mV within 1 min. In voltage clamp experiments, exposure to Cs blocks both the pacemaker current iK2 and the instantaneous outward current iK1, while the delayed outward rectifying potassium current ix is not affected. In the presence of 20 mM Cs, the steady state currents are related linearly to the clamp potential and are insensitive to alterations in [K]0. The Cs sensitive current was defined as the difference between control and membrane currents measured in the presence of 20 mM Cs. This current displays inward-going rectification and its reversal potential follows log E1K]0 with a slope of 60 mV per decade.
Insights
Cesium (Cs) blocks cardiac Purkinje fiber currents iK2 and iK1, altering membrane potential. The Cs-sensitive current shows inward rectification, with a reversal potential dependent on external potassium concentration.
Area of Science:
- Cardiovascular Physiology
- Electrophysiology
- Ion Channel Function
Background:
- Cardiac Purkinje fibers possess unique electrical properties crucial for heart rhythm.
- Ion channels, particularly potassium channels, play a vital role in regulating cardiac membrane potential.
Purpose of the Study:
- To investigate the effects of Cesium (Cs) on cardiac Purkinje fiber membrane potential and ion currents.
- To characterize the properties of Cs-sensitive currents in these cells.
Main Methods:
- Voltage clamp experiments were performed on cardiac Purkinje fibers.
- The effects of 20 mM Cesium (Cs) on membrane currents were analyzed.
- The Cs-sensitive current was isolated by subtracting currents in the presence of Cs from control currents.
Main Results:
- Exposure to 20 mM Cs caused a rapid decrease in membrane potential to -60 mV.
- Cesium blocked the pacemaker current (iK2) and instantaneous outward current (iK1), but not the delayed outward rectifying potassium current (iK).
- The Cs-sensitive current exhibited inward-going rectification, and its reversal potential correlated with external potassium concentration ([K]0).
Conclusions:
- Cesium selectively blocks specific potassium currents (iK2 and iK1) in cardiac Purkinje fibers.
- The identified Cs-sensitive current demonstrates inward rectification, suggesting a distinct functional role.
- The dependence of the reversal potential on [K]0 provides insights into the ionic basis of this current.