Pores, Channels and Transporters
It is clear from the data presented in Chapter 7 that the phospholipid bilayer is a very effective barrier to most small molecule solutes. Yet, there is a constant flux of polar and ionic substances across the cell plasma membrane, as well as across the membranes defining various organelles such as the mitochondria. This mass transport is all protein-mediated, and a wide variety of mechanisms have been elucidated by which solute flux across membranes is achieved. It is the primary purpose of this chapter to present a survey in which the general question addressed is how matter gets across a biomembrane. The next chapter addresses the question of how information is transmitted across the membrane and covers topics related to cellular communication, surface receptors, and signal transduction. The material in these two chapters is interrelated. For example, one response to certain signals (e.g., a molecule binding to a cell surface receptor) is to alter rapidly the membrane permeability to specific ions, resulting in an alteration in the transmembrane potential and/or changes in the intracellular concentration of the ions. Before discussing this and other mechanisms of signal transduction, however, it is important to understand how the cell regulates which molecules exit and enter various cellular compartments.
KeywordsSodium Channel Nicotinic Acetylcholine Receptor Transmembrane Potential Planar Membrane Free Energy Profile
Unable to display preview. Download preview PDF.