Development and Evaluation of Novel Solution Pairs to Enhance Seal Resistance in Automated Patch Clamp Experiments

Gigaohm seals, or ‘gigaseals’, are crucial for patch clamp electrophysiology, ensuring excellent electrical access to cells to enable high-quality recordings. These seals form through chemical bonds and electrostatic forces between the cell membrane and the glass pipette in manual patch clamp, or between the cell membrane and chip substrate in planar patch clamp. Planar patch clamp often employs ‘seal enhancers’ to increase seal resistances, with CaF2 being the most commonly used. It is hypothesized that high extracellular Ca2+ and intracellular F- concentrations lead to CaF2 precipitate formation at the solution interface, promoting seal formation.
However, CaF2 as a seal enhancer has limitations. F- interacts with various internal components such as protein kinase A, adenylate cyclase, and lipid phosphatases, which can affect the biophysical properties of some ion channels. Additionally, F- is not ideal when recording from Ca2+- activated ion channels due to the resulting unknown concentrations of free intracellular Ca2+.
This study evaluates alternative insoluble salt pairs that provide the same seal-enhancing effect as CaF2 without the unwanted side effects of F-. Although there was no correlation between the different salt Ksp values and their ability to foster gigaseal formation, BaSO4 was identified as an equivalent seal enhancer to CaF2 in planar patch clamp electrophysiology. BaSO4 and CaF2 were characterized across two different ion channels, hNav1.5 and hCav1.2. While increasing concentrations of F- caused depolarizing shifts in the voltage dependence of inactivation of hNav1.5, SO42- had no effects on hNav1.5 biophysical properties. Additionally, pharmacological values were comparable between both solution pairs. In conclusion, we identified BaSO4 as an alternative salt pair to enhance seal resistances in automated patch clamp experiments.