Commercial cuvettes come with different gap sizes between the electrodes.
Typically a cuvette for bacteria will have a gap of 1mm
A cuvette for mammalian transefction will have a gap of 2mm or 4mm.
I appreciate that field strength plays an important role in successful electroporation and the gap distance has a bearing in field strength
Ec=Vc/(0.75 x dcell)
Where Ec= Critical field strength (V/cm)
Vc = Permeation voltage of the membrane (1V @ 22 deg C and 2V @ 4 deg C)
dcell= diameter of cell
For calculating the voltage to be set on the electroporator, the field strength Ec is multiplied by the gap width of the
V = Ec x dcuv
V = Ec x dcuv
V: Voltage (setting on Multiporator) [V]
Ec: Critical field strength [V/cm]
dcuv: Electrode distance (cuvette type) [cm]
This means at room temp Ec of a 20uM cell will be 667 V/cm
and in a 1mm cuvette voltage required for poration will be 66.7V
and in a 2mm cuvette 133 V and 4mm cuvette 267 V.
I therefore ask why do people use 2mm and 4mm cuvettes for mammalian cell electroporation and not use 1mm cuvettes and lower voltages?
Does it have something to do with increases in resistance (which would reduce current for a given voltage [I=V/R]) with the smaller gap between the electrodes? Or is it just because to electroporate 500000 mammalin cells takes a larger volume than 500000 bacterial cells?