WPI EVOM3 - Appendix F: Resistance Calculations

EVOM3
World Precision Instruments 41
APPENDIX F: RESISTANCE CALCULATIONS
Resistance
The value of the blank (control well) always adds to the total resistance measured
across a tissue culture membrane. The blank resistance must be measured and then
subtracted from the resistance reading across the tissue in order to obtain the true
tissue resistance. For example, suppose the resistance through a 0.15 M KCl solution
and across the membrane support (with no tissue present) of a 12-well cell culture
insert measures 130 Ω This is the blank or control reading for that cell culture insert.
(Resistance may vary for culture cups made by other manufacturers.) In this example,
ing  Ω a the amle meaement, the allated eitane  the tie itel
(R tissue) is:
R
Total
  Ω
R
blank
  Ω
R
blank
 R
true tissue
 R
Total
R
true tissue
 R
Total
- R
blank
R
true tissue
  Ω   Ω   Ω
Resistance Value of the “Blank” Insert
When using an EVOM3 with an STX2-PLUS to measure a blank insert, the resistance
ale i tiall eteen  t  Ω, deending n the eifi and  the inet,
and lower in EndOhms. This is not background resistance due to the resistance of the
lan filte Rathe, i the filte memane i emed m the inet, the eitane
reading of the insert will remain nearly the same, because the background resistance
eading i de mainl t the eletde ga, id eitane, the mall ga eteen
the bottom of the cell culture insert and the bottom of the cell culture plate. See Fig.
54. For a Millipore insert this gap is about 1 mm, with some insert brands having a
lightl lage ga than the he aiatin in thi ga i the ae  the dieene
eteen lan eading  dieent and he malle the ga, the highe the
eleti eitane he eitane  the filte memane itel i atall negligile
If an ENDOHM-24G-SNAP or ENDOHM-12G chamber is used, the blank resistance
eme nea e, eae the etenal eletde i dietl ndeneath the filte
and the gap does not exist.