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Outward current and electrogenic sodium pump in Purkinje fibers
Abstract:
The effects of metabolic inhibitors (ouabain, dihydroouabain, and 2,4-dinitrophenol (2,4-DNP) and of cooling on the membrane current of Purkinje fibers were studied by means of a voltage clamp. Within seconds after cooling or application of the drugs the outward current was found to be reduced. On longer cooling or poisoning, the potassium equilibrium potential was shifted in positive direction, the time-dependent membrane currents were depressed, and possibly the potassium conductance was altered. It is suggested that the early reduction in outward current is caused by inhibition of an electrogenic sodium pump.
Insights
Metabolic inhibitors and cooling reduce outward membrane current in Purkinje fibers. This early reduction is likely due to inhibition of the electrogenic sodium pump, affecting ion transport.
Area of Science:
- Cardiovascular Physiology
- Cellular Electrophysiology
Background:
- Purkinje fibers play a crucial role in cardiac impulse propagation.
- Membrane currents are essential for cardiac electrical activity and are influenced by metabolic state.
Purpose of the Study:
- To investigate the impact of metabolic inhibition and hypothermia on Purkinje fiber membrane currents.
- To elucidate the mechanisms underlying changes in membrane current under these conditions.
Main Methods:
- Utilized voltage clamp techniques to precisely measure membrane currents in Purkinje fibers.
- Applied metabolic inhibitors (ouabain, dihydroouabain, 2,4-dinitrophenol) and controlled cooling.
Main Results:
- Rapid reduction in outward membrane current observed upon cooling or drug application.
- Prolonged cooling or inhibition led to a positive shift in potassium equilibrium potential.
- Time-dependent membrane currents were depressed, with potential alterations in potassium conductance.
Conclusions:
- The early decrease in outward current is attributed to the inhibition of the electrogenic sodium pump.
- Metabolic stress significantly alters Purkinje fiber electrophysiology, impacting ion gradients and membrane excitability.