Electric current generated by squid giant axon sodium pump: external K and internal ADP effects

Area of Science:

• Neuroscience
• Cellular Physiology
• Biochemistry

Background:

• The sodium pump (Na+/K+-ATPase) is crucial for maintaining cellular ion gradients.
• Understanding its stoichiometry and electrogenic properties is key to cellular function.

Purpose of the Study:

• To investigate the stoichiometry and electrogenic behavior of the sodium pump in squid giant axons.
• To explore how intracellular ADP levels and external potassium concentrations affect pump function.

Main Methods:

• Simultaneous measurement of sodium efflux using 22Na and transmembrane current.
• Calculation of pump-generated current from membrane resistance and digitalis-sensitive membrane potential.
• Manipulation of intracellular ADP levels via L-arginine injection.

Main Results:

• In normal axons, Na:K pump stoichiometry (3:2) is constant across varying external potassium (K+) levels.
• Elevated ADP levels induce electroneutral Na:Na exchange in the absence of external K+.
• High-ADP axons exhibit increased electrogenic pumping with rising external K+, altering charge translocation per extruded sodium.

Conclusions:

• The Na:K pump stoichiometry is relatively stable under normal conditions.
• Intracellular ADP levels significantly influence the mode of sodium transport by the pump.
• Extracellular potassium modulates the electrogenic nature of the sodium pump, particularly under conditions of elevated ADP.