Regional electroporation of single cardiac myocytes in a focused electric field

There is now a significant interest in being able to locate single cells within geometrically defined regions of a microfluidic chip and to gain intracellular access through the local electroporation of the cell membrane. This paper describes the microfabrication of electroporation devices which can enable the regional electroporation of adult ventricular myocytes, in order to lower the local electrical resistance of the cell membrane. Initially three different devices, designed to suit the characteristic geometry of the cardiomyocyte, were investigated (all three designs serve to focus the electric field to selected regions of the cell). We demonstrate that one of these three devices revealed the sequence of cellular responses to field strengths of increasing magnitudes, namely, cell contraction, hypercontraction, and lysis. This same device required a reduced threshold voltage for each of these events, including in particular membrane breakdown. We were not only able to show the gradual regional increase in the electric conductivity of the cell membrane but were also able to avoid changes in the local intra- and extracellular pH (by preventing the local generation of protons at the electrode surface, as a consequence of the reduced threshold voltage). The paper provides evidence for new strategies for achieving robust and reproducible regional electroporation, a technique which, in future, may be used for the insertion of large molecular weight molecules (including genes) as well as for on-chip voltage clamping of the primary adult cardiomyocyte.