problems with MTS test

[rsegreto]

Hi,

I have used the MTS test (commercial kit) for the first time to verify the viability of insect tissues after cryopreservation with culture medium, glycerol and FBS at -80. Since we work with tissues and not with single cells I weighted the tissue used (about 0.02 g). Beside the test on the cryopreserved samples (1), I tested the effect of glycerol on the viability of the tissues at room temperature (2), and added a positive control (only tissue in culture medium) (3), and a negative control (tissue in the culture medium directly stored at -80 without glycerol and FBS for 24 h) (4). I measured the absorbance at 490 as described in the kit. The absorbance in (1), (2) and (3) had a maximum after 1h and then went down again. (3) had an average abs. of 0.5 and (1) and (2) of about 0.2. The problem is that the negative control (4) gave also an abs. of about 0.2 (in this case the value did not change with the time). Was the tissue still alive? Did I use too much tissue?
If someone has experience with the use of this test and could help me to interpret these results I would really appreciate it.

Rossana