Patch-Clamp and Perfusion Techniques to Study Ion Channels Expressed in Xenopus Oocytes.

The Xenopus oocyte expression system is ideal for electrophysiological characterization of voltage-dependent and ligand-dependent ion channels because of its relatively low background of endogenous channels and the large size of the cell. Here, we present a protocol to study voltage- and ligand-dependent activation of ion channels expressed in Xenopus oocytes using patch-clamp techniques designed to control both the membrane voltage and the intracellular solution. In this protocol, the large conductance voltage- and Ca2+-activated K+ (BK) channel is studied as an example. After injection of BK channel mRNA, oocytes are incubated for 2-7 d at 18°C. Inside-out membrane patches containing single or multiple BK channels are excised with perfusion of different solutions during recording. The protocol can be used to study structure-function relations for ion channels and neurotransmitter receptors.