Comparison of Cell Expression Formats for the Characterization of GABA A Channels Using a Microfluidic Patch Clamp System

Abstract

Ensemble recording and microfluidic perfusion are recently introduced techniques aimed at removing the laborious nature and low recording success rates of manual patch clamp. Here, we present assay characteristics for these features integrated into one automated electrophysiology platform as applied to the study of GABA_A channels. A variety of cell types and methods of GABA_A channel expression were successfully studied (defined as I_GABA>500 pA), including stably transfected human embryonic kidney (HEK) cells expressing α₁β₃γ₂ GABA_A channels, frozen ready-to-assay (RTA) HEK cells expressing α₁β₃γ₂ or α₃β₃γ₂ GABA_A channels, transiently transfected HEK293T cells expressing α₁β₃γ₂ GABA_A channels, and immortalized cultures of human airway smooth muscle cells endogenously expressing GABA_A channels. Current measurements were successfully studied in multiple cell types with multiple modes of channel expression in response to several classic GABA_A channel agonists, antagonists, and allosteric modulators. We obtained success rates above 95% for transiently or stably transfected HEK cells and frozen RTA HEK cells expressing GABA_A channels. Tissue-derived immortalized cultures of airway smooth muscle cells exhibited a slightly lower recording success rate of 75% using automated patch, which was much higher than the 5% success rate using manual patch clamp technique by the same research group. Responses to agonists, antagonists, and allosteric modulators compared well to previously reported manual patch results. The data demonstrate that both the biophysics and pharmacologic characterization of GABA_A channels in a wide variety of cell formats can be performed using this automated patch clamp system.