30] Unidirectional fluxes through ion channels expressed in Xenopus oocytes

Abstract

Publisher Summary The measurement of unidirectional fluxes of substances across the plasma membrane of cells is a valuable tool for understanding many membrane transport processes. The movement of electrically charged substances can be followed with electrical current measurements, but the use of radiolabeled tracers is one of very few ways to assess the transport of uncharged molecules. Even though electrical current can monitor the net flux of ions, additional valuable information is contained in the unidirectional ion influx and efflux. In particular, the ratio of unidirectional fluxes through the pores of ion channels provides rather direct information on the number of ions that may simultaneously occupy the pore. This chapter is to describe some methods useful for measuring the unidirectional influx and efflux of K + ions through channels expressed in Xenopus oocytes. Specifically, these techniques have been applied to the question of the number of K + ions that simultaneously occupy the pore of Shaker and IRK1 K + channels. Even though designed for the determination of unidirectional ion fluxes through ion channels, many of the methods described here could be applied to the measurement of the unidirectional fluxes of other substances.