Abstract
Many ion channels show low basal activity, which is increased hundreds-fold by the relevant gating factor. A classical example is the activation G-protein-activated K(+) channels (GIRK) by Gbetagamma subunit dimer. The extent of activation (relative to basal current), R(a), is an important physiological parameter, usually readily estimated from whole cell recordings. However, calculation of R(a) often becomes non-trivial in multi-channel patches because of extreme changes in activity upon activation, from a seemingly single-channel pattern to a macroscopic one. In such cases, calculation of the net current flowing through the channels in the patch, I, before and after activation may require different methods of analysis. To address this problem, we utilized neuronal GIRK channels activated by purified Gbetagamma in excised patches of Xenopus oocytes. Channels were expressed at varying densities, from a few to several hundreds per patch. We present a simple and fast method of calculating I using amplitude histogram analysis and establish its accuracy by comparing with I calculated from event lists. This method allows the analysis of extreme changes in I in multichannel patches, which would be impossible using the standard methods of idealization and event list generation.