The Na:K pump in red cells is electrogenic.

Area of Science:

• Cellular Physiology
• Membrane Biophysics
• Ion Transport

Background:

• The membrane potential (E) of red blood cells is crucial for cellular function.
• The Na:K pump plays a vital role in maintaining ion gradients and membrane potential.
• Understanding the electrogenic nature of the Na:K pump requires specific experimental conditions.

Purpose of the Study:

• To investigate the electrogenic contribution of the Na:K pump to red blood cell membrane potential.
• To determine the membrane resistance (Rm) of red blood cells using pump activity.
• To compare Rm values derived from pump current and residual sulfate flux.

Main Methods:

• Measurement of red blood cell membrane potential (E) using the fluorescent dye 3,3'-dipropylthiadicarbocyanine iodide.
• Activation of the Na:K pump with external potassium (K+) and inhibition with ouabain.
• Experimental manipulation of intracellular sodium (Na+), external chloride (Cl-), and sulfate (SO2-(4)) permeability using 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS).

Main Results:

• Na:K pump activation caused hyperpolarization, while ouabain addition led to depolarization of the red cell membrane potential.
• The electrogenic component of the Na:K pump contributed approximately 6 mV to membrane potential changes in human red cells.
• Membrane resistance (Rm) was estimated to be around 1 X 10(6) ohm-cm2 in human red cells, consistent between pump-dependent and sulfate flux measurements.

Conclusions:

• The Na:K pump is a significant electrogenic component in red blood cells, directly affecting membrane potential.
• Membrane resistance (Rm) can be reliably estimated from the electrogenic activity of the Na:K pump.
• The net current flow across the red blood cell membrane is largely accounted for by the Na:K pump's transport activity.