Electrophysiological Recordings from Xenopus Oocytes

Abstract

A major goal of electrophysiology is to understand, at a molecular level, how an ion channel functions. How does ion permeation occur, how do channels activate and inactivate, how does it sense changes in the electric field, and how is the channel regulated? Our understanding of these fundamental processes has been severely hampered by the lack of a suitable experimental model system. Most cells simultaneously express a plethora of different channels, and it is therefore extremely difficult to study one type of channel in isolation. This is usually achieved by using complex voltage protocols and solutions rich in ion channel blockers and nonpermeant ions, neither of which is likely to be relevant physiologically. Moreover, it is not possible to artificially and systematically manipulate the channel gene in an intact cell, thereby precluding structure—function characterization. What is needed is a cell that has few endogenous ionic conductances and into which the channel under investigation can be exogeneously expressed. These criteria are adequately fulfilled by the Xenopus oocyte expression system. Following the key observation of Gurdon et al. in 1971 that foreign RNA injected into oocytes could be translated into proteins, Gundersen et al. (1983) and Miledi et al. (1983) were the first to demonstrate that a variety of receptors and channels from the central nervous system could be functionally expressed in the oocyte. The recent dramatic advances in both molecular biology, where proteins can be routinely cloned and mutated at specific loci, and electrophysiology (predominantly patch clamp) have combined to produce a powerful approach to the study of ion channels.