抄録
The streaming potential (Vstream) is an outcome of the electroosmosis that arises from coupled flux of ion and water in the pore. Vstream gives quantitative information on the coupling ratio of ion-water flux and, thus, it is prerequisite for investigating ion permeation mechanisms. Vstream is evaluated as a shift of the reversal potential (Vrev) upon changes in osmotic gradient. Measurements of Vstream are, however, technically challenging. High osmotic gradient must be imposed across the membrane and planar bilayer method has been used exclusively. Moreover, the value of Vstream is so small that precise evaluation of Vrev is necessary. Here, we developed a novel method for measuring Vstream under the whole-cell patch-clamp configuration. Two features are essential in this method. Firstly, exposure time to high osmotic gradient was defined for short period of time by the ultra-fast solution-exchange system, thus circumvented cellular damages and subsequent responses. Secondly, Vrev was evaluated with great accuracy from macroscopic current measurements upon a series of ramp command. Whole time courses of current traces during a ramp voltage were used for optimizing the parameters of an equivalent membrane circuit. We applied this method to HERG potassium channel expressed in HEK293 cells and revealed that the ion-water coupling ratio changed with potassium concentration. [Jpn J Physiol 55 Suppl:S136 (2005)]
