NaGradient

NaGradient refers to the electrochemical gradient of sodium ions (Na+) across a biological membrane. It results from the difference in Na+ concentration between the compartments (typically high extracellular Na+ and much lower intracellular Na+) and the electrical potential difference across the membrane. Together, these factors define a driving force for Na+ movement that can be exploited by channels, transporters, and pumps.

In many animal cells, extracellular Na+ is about 140 mM while the cytoplasm contains roughly 10–15 mM Na+. The resting membrane potential is commonly around −60 to −70 mV. According to the Nernst equation, the equilibrium potential for Na+ is typically around +60 to +70 mV, indicating a strong tendency for Na+ to enter the cell if a pathway is available. The overall gradient is actively maintained by the Na+/K+-ATPase, which exports three Na+ ions for every two K+ ions imported, using ATP. This pump sustains the gradient against leak currents and supports secondary active transport.

The NaGradient underpins a range of physiological processes. In neurons and muscle cells, it powers action potentials via rapid Na+ influx through voltage-gated Na+ channels, followed by repolarization through K+ efflux. It also drives secondary transporters, such as Na+-coupled glucose cotransporters, and contributes to renal and intestinal reabsorption of solutes.

Disruption of the gradient, whether by metabolic failure, toxins, or ischemia, impairs excitability and transport and can contribute to cellular injury. The NaGradient is therefore a fundamental parameter in cellular physiology and pharmacology.