Recording of Endogenous GABAA Channel in Human Airway Smooth Muscle Cells using the IonFlux System

Classical cell based screening assays employ cell lines in which the channel under study has been transfected to achieve elevated levels of channel expression. However, dis- parities exist between experimental results of screening assays using cells over ex- pressing the target of interest as compared to cells found in vivo with endogenous levels of ion channel expression. This has raised concerns regarding the physiological relevance of the screening. In non- transfected cells, the assay targets are expressed in a more physiologically relevant environment, and the complex interplay of the endogenously expressed ion channels, secondary messengers and other cell signaling proteins can be better recapitulated than in the recombinant cell lines. Therefore, there is a growing interest in the use of non-transfected cells for drug discovery screening.
Patch clamp recording is the gold standard in studying ion channels. Automated patch clamp (APC) systems can achieve higher throughput than the conventional manual patch clamp and are less labor intensive, which allow greater capacity to conduct ion channel screening. To date, the most common APC assays use transfected cell lines. It is of great interest to explore the capability of the APC system recording of endogenous channels in non-transfected cells to achieve maximal native cell physiological relevance for compound screening studies.
In this report, we present recordings from endogenous GABAA channels in human air- way smooth muscle cells using IonFlux automated patch clamp system. Dr. Charles Emala’ s group (Columbia University) is the first to demonstrate the expression and function of endogenous ionotropic GABAA channels on human smooth muscle cells 1. We show that IonFlux system can measure currents of these endogenous GABAA channels on the smooth muscle cells with a high success rate, and good quality whole cell, loose patch current.