Patch-clamping of primary cardiac cells with micro-openings in polyimide films

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Abstract
Patch-clamping is a powerful method for investigating the function and regulation of ionic channels. Currently, great efforts are being made to automate this method. As a step towards this goal, the feasibility of patch-clamping primary cells with a microscopic opening in a planar substrate was tested. Using standard microfabrication and ion beam technology, small-diameter openings (2 and 4 μm) were formed in polyimide films (thickness 6.5 μm). Single cells (sheep Purkinje heart cells, Chinese hamster ovary cells) in a suspension were positioned on top of the opening and sucked towards the opening to improve adhesion of the cell to the planar substrate, hence increasing the seal resistance. Voltage/current measurements yielded a median seal resistance of 1.3MΩ with 4 μm openings (n=24) and 26.0 MΩ with 2 μm openings (n=75), respectively. With 2 μm openings, successful loose-patch recordings of TTX-sensitive inward currents and action potentials in sheep Purkinje heart cells (n=18) were made. In rare cases, gigaseals (n=4) were also measured, and a whole-cell configuration (n=1) could be established. It was concluded that the simple planar patch approach is suitable for automated loosepatch recordings from cells in suspension but will hardly be suitable for highthroughput whole-cell patch-clamping with high-resistance seals.