Electrogenic sodium pump in rabbit atrio-ventricular node cell

Area of Science:

• Cardiovascular Physiology
• Electrophysiology
• Cellular Electrogenesis

Background:

• The electrogenic nature of the sodium-potassium pump (Na pump) is crucial for cellular function in excitable tissues.
• Understanding the Na pump's role in the atrioventricular (A-V) node is vital for comprehending cardiac rhythm regulation.

Purpose of the Study:

• To demonstrate the electrogenicity of the Na pump in rabbit A-V node cells.
• To characterize the Na pump's activation by monovalent cations and its contribution to membrane potential.

Main Methods:

• Analysis of potassium (K)-induced hyperpolarization in rabbit A-V node cells following K-free perfusion.
• Application of strophanthidin to assess Na pump inhibition.
• Measurement of membrane slope conductance and cation activation potencies.

Main Results:

• Transient hyperpolarization, abolished by strophanthidin, indicated Na pump electrogenicity.
• Hyperpolarization exceeded the expected equilibrium potential for K+ (EK), reaching -69 mV.
• Monovalent cation activation followed the order Tl > Rb ≈ K > NH4 ≈ Cs > Li, consistent with known Na pump kinetics.
• Michaelis-Menten kinetics characterized the K+ site activation of the Na pump.

Conclusions:

• The Na pump in A-V node cells exhibits electrogenic properties similar to other excitable tissues.
• Direct contribution of Na pump activity to the physiological membrane potential was observed.
• These findings highlight the Na pump's significance in A-V node function and cardiac electrophysiology.