Membrane Transporter/Ion Channel

Membrane transporters and ion channels are encoded by numerous gene families with 406 genes encoding ion channels and 883 encoding a broad variety of transporters, of which 350 were classified as intracellular transporters. Many of these proteins play key roles in pharmacology, affecting entry and extrusion of drugs into and out of cells. In particular, ATP-binding cassette (ABC) transporters, such as the multiple drug resistance transporter MDR1 (multidrug resistance 1, ABCB1 or P-glycoprotein), mediate energy-dependent drug efflux and play a main role in chemoresistance.Most of molecules enter or leave cells mainly via membrane transport proteins, which play important roles in several cellular functions, including cell metabolism, ion homeostasis, signal transduction, binding with small molecules in extracellular space, the recognition process in the immune system, energy transduction, osmoregulation, and physiological and developmental processes. 
There are three major types of transport proteins, ATP-powered pumps, channel proteins and transporters. Ion channels are expressed in many cancers and contribute to disease progression. A number of ion channels are well established as clinical targets for a range of (noncancer) pathologies. This chapter will introduce the principal ion channel classes that have been identified in cancer cells, including those permeant to K+, Na+, Ca2+, and Cl−, and their functional role. Particularly important is that in addition to regulating ion flux, a number of ion channels also play critical roles in nonconducting signaling pathways, eg, via cell–cell or cell–substrate adhesion, and interaction with manifold intracellular signaling partners and cascades.