The molecular basis of electrical signaling is that nerve cells maintain ion concentration gradients across their surface membranes, which allows one or more of these ions (Na+, K+, Cl–, and Ca2+) to diffuse down their electrochemical gradients and form electrical signaling transduction effects. The work of generating and maintaining ionic concentration gradients for particular ions is carried out by a group of plasma membrane proteins known as active transporters.
Moving ions uphill requires the consumption of energy, and neuronal transporters fall into two classes based on their energy sources:
1) ATPase pumps refer to transporters that acquire energy directly from the hydrolysis of ATP.
The most prominent example of an ATPase pump is the Na+ pump (or, more properly, the Na+/K+ ATPase pump), which is responsible for maintaining transmembrane concentration gradients for both Na+ and K+.
Another is the Ca2+ pump, which provides one of the main mechanisms for removing Ca2+ from cells.
2) Ion exchangers are a kind of transporters that does not use ATP directly, but depends instead on the electrochemical gradients of other ions as an energy source. This type of transporter carries one or more ions up its electrochemical gradient while simultaneously taking another ion (most often Na+) down its gradient. Because at least two species of ions are involved in such transactions, these transporters are usually called ion exchangers.
An example of such a transporter is the Na+/Ca2+ exchanger, which shares with the Ca2+ pump the important job of keeping intracellular Ca2+ concentrations low.
Another exchanger in this category regulates both intracellular Cl– concentration and pH by swapping intracellular Cl– for another extracellular anion, bicarbonate.
Na+/H+ exchanger, also regulate intracellular pH, in this case by acting directly on the concentration of H+.
Purves D, Augustine G J, Fitzpatrick D, et al. Neuroscience, chapter 4[J]. 2004.