Cell Membrane Transport

Abstract

Oscar Wilde obviously was not attempting to describe the importance of the ion-conducting channels, the energy-driven pumps, or the other systems which are involved in transporting calcium ions across membranes — because if he had he might have chosen his words more carefully. The mechanisms which are involved in maintaining intracellular ionic homeostasis, particularly with respect to Ca²⁺ and Na⁺, are complex but gradually the relative significance and modus operandi of these systems is being untangled. Thus it is now well established that the ionic composition of the cytosol in excitable cells, including cardiac and smooth muscle cells, is controlled to a large extent by the semipermeable hydrophobic barrier provided by the plasma membrane, since it is this membrane which prevents the free movement of ions along their concentration gradients. The controlled movement of selected ions across these and other membranes involves a network of membrane-spanning proteins. These membrane spanning proteins can be subdivided into four main classes.

“There is nothing improbable about my explanation at all In fact it is perfectly ordinary.”

Oscar Wilde in, “The Importance of Being Earnest.”