Sodium-dependent transporters in health and disease—a special issue

Abstract

Sodium-dependent transporters utilize the energy stored in the transmembrane sodium gradient to move ions or other solutes against their concentration gradient across the plasma membrane. This sodium gradient is established and maintained by the sodium pump or Na + –K + ATPase that directly hydrolysis ATP. The Na + –K + ATPase pumps three sodium ions out of the cell in concert with pumping two potassium ions into the cell, thus maintaining an intracellular environment that has low sodium and high potassium (the opposite of extracellular fluid). In most cells, 50 % of the total energy expended is used to run these ion pumps. In neurons, which repeatedly gain sodium during action potentials, two thirds of the ATP usage goes toward fueling this single pump. Sodium-dependent transporters belong to the class of cotransporters including symporters and antiporters. Some of which carry both solutes in the same direction (symport), while others transport sodium into the cell and anion or solute out of the cell (antiport). In general, cotransporters are one of three main classes of integral membrane proteins known as transporters that move solutes and ions across the plasma membrane. The cotransporters belong the solute carrier (SLC) group of membrane transport with nearly 400 members organized into 52 families [2, http://slc.bioparadigms.org/]. The SLC gene nomenclature system was originally proposed