Examples of Applications of Electrophysiology

All the techniques that we have discussed, flux measurements, steady-state and transient current measurements, as well as single-channel recordings and the corresponding analysis can be applied to the analysis of structure-function relationships. Such structure-function information can be obtained if we characterize and compare the function of wild-type and chemically or genetically modified transporters by using these techniques. The latter also includes naturally occurring mutations that are the source of various diseases; this is an important feature for the understanding and curing of such diseases. For many of the transporters the amino acid sequence and the possible orientation of the protein in the membrane, or even the three-dimensional structures have been determined. In this chapter on Examples of Applications of Electrophysiology, we will illustrate the strategy of an electrophysiologist in investigating structure, function and regulation of membrane transport using as an example the Na(+),K(+)-ATPase, the neurotransmitter transporter GAT (Na(+)-dependent GABA transporter), and the nucleotide receptors that form channels in the presence of extracellular ATP. For an understanding of drug action as well as the development of new drugs for the treatment of diseases, electrophysiology is a powerful method to elucidate drug receptor interaction. As an example, this will be illustrated for viral ion channels that are essential for virus reproduction.