Introduction

The field of electrophysiology explores the mechanisms of electrical signal generation and propagation in living tissues. Contemporary electrophysiology has tended to focus on electrically excitable cells, for example observing action potentials propagating along a neuronal membrane. However, the birth of electrophysiology was concerned with a more global approach, looking at “bioelectricity” in the whole organism. Galvani, the father of “bioelectricity”, hooked up lightning rods to cut nerves in a frog’s leg and observed twitching of the leg muscles during a lightning storm. Matteucci, in 1831, was the first to measure the so-called “injury potentials” using a galvanometer in a cut nerve ending and demonstrated the existence of action potentials in nerves and muscles. His work was extended by Du Bois-Reymond, who in 1843 was able to directly measure the propagation of action potentials and also the injury potentials from cuts in his own finger. While rapid changes in membrane conductance of individual cells may be viewed as a somewhat “obvious” target that has been intensely studied, other, slower bioelectric phenomena such as those seen in wound healing have been somewhat neglected. The field of “bioelectricity” has seen a re-emergence in the past decade, thanks in part to new techniques in molecular physiology. In addition, the ensemble of electric phenomena in biology is rarely considered. Instead of solely focusing on action potentials in individual cells, it can be instructive to consider electrical characteristics in groups or arrays of cells. In this chapter we focus on the electrical measurement of arrays of cells or tissue layers. We attempt to widen the traditional definition of electrophysiology in a more general sense, as the electrical measurement of ion flow in biological systems. We review a subset of literature on methods for measuring ion flow in tissues in vitro in both electrically active and non-electrically active cells. We will particularly highlight dynamic methods for monitoring cell cultures, and the new trend of using transistors rather than simple electrodes with a special emphasis on the use of conducting polymers to do so.