An In Vitro Fluorescence-Based Assay to Measure Plasma Membrane Resealing Efficiency

To set up a high throughput fluorescence-based assay for the repair permissive conditions, wash the cells two times with 200 microliters of 37 degrees Celsius M1 medium per well, and add 100 microliters of fresh 37 degrees Celsius M1 medium supplemented with 30-micromolar propidium iodide after discarding the second wash.

For repair restrictive conditions, wash the cells one time with 200 microliters of 37 degrees Celsius M2 medium supplemented with 5-millimolar EGTA per well, followed by one wash with 200 microliters of M2 medium alone.

After discarding the second wash, add 100 microliters of fresh 37 degrees Celsius M2 medium supplemented with 30-micromolar propidium iodide per well. Then, image the plate under transmitted light, GFP, and PI, as just demonstrated. While the plate is being imaged, place a 96-well round-bottom polypropylene microplate on ice, and configure the plate as just demonstrated for the previous plate.

For repair permissive conditions, add 100 microliters of ice-cold M1 medium supplemented with 60 micromolar propidium iodide per well, followed by the addition of 100 microliters of ice-cold M1 with or without 4x listeriolysin O per well.

For repair restrictive conditions, add 100 microliters of ice-cold M2 medium supplemented with 60 micromolar propidium iodide per well, followed by the addition of 100 microliters of ice-cold M2 with or without 4x listeriolysin O per well.

It is imperative to prepare listeriolysin O at the appropriate experimental concentration on ice approximately 5 minutes prior to the start of the kinetic assay when plate 1 is on ice and plate 2 is being prepared.

When the first plate is finished imaging, immediately transfer the plate onto a sheet of aluminum foil on ice. After 5 minutes, transfer 100 microliters from each well of the second plate to the appropriate corresponding well in the first cooled plate, inserting the pipette tips below the meniscus of solution in each well before ejecting the volume without mixing for proper distribution of the toxin.

Allow the toxin to bind to the host cells for 1 minute, and immediately transfer the first plate to the plate reader for the postkinetic assay using the spectrofluorometer mode. At the end of the kinetic assay, immediately acquire a postkinetic imaging of the plate image as demonstrated for the prekinetic imaging.