Ion channels, receptors, agonists and antagonists

This article describes the physiology of ion channels and their modulation by commonly used drugs in anaesthesia and intensive care. It should give the clinician a better understanding of ion channel physiology and the molecular mechanisms underpinning the actions of drugs used in an acute-care setting. The concept of efficient and selective transport of ions across ‘impermeable’ plasma membranes is introduced, together with the mechanisms responsible for electrochemical signalling within cells. The classification and composition of voltage-gated ion channels are described in the context of their contribution to action potential generation in excitable cells. Drug–receptor interaction of the four main classes of receptor (ligand-gated ion channels, G-protein-coupled, enzyme-linked and nuclear receptors) and the associated signal-transduction mechanisms that initiate the cascades of intracellular events to control cellular function are also discussed. Finally, the principles of drug–receptor interaction of agonists, antagonists and inverse agonists are discussed in relation to their affinity, efficacy and potency.