Seal-promoting solutions and pipette perfusion for patch clamping plant cells

Patch-clamp technology has greatly increased our knowledge of plant membrane transport. However, the success of patch clamping crucially relies on establishing a high resistance (GΩ) seal between the membrane and the patch-clamp pipette. This can prove problematic in many plant-cell preparations. It is therefore of great importance to develop protocols for protoplast isolation, maintenance and seal formation that improve seal rate. This study investigated whether the pH and the K⁺ and the Cl^- concentration of the pipette solution had an effect on the seal formation. High pH and absence of K⁺ significantly promoted membrane sealing, whereas the concentration of Cl^- had no effect. To reap the benefit of seal-promoting pipette solutions and yet retain the option to adjust this solution to experimental requirements, a pipette perfusion apparatus was implemented. The perfusion system was successfully applied in cell-attached patch, excised-patch and whole-cell configurations, using plasma membrane and tonoplast of three different species. The system enables complete solution exchange within minutes end is potentially of great benefit in the study of channel selectivity, the application of (cytoplasmic) channel blockers and the study of primary and secondary transport.