Cell Counting kit-8 (CCK-8) and Cell Counting Kit-SK (CCK-SK) allows convenient assays using Dojindo’s proprietary tetrazolium salt, WST-8. This produces a water soluble formazan dye upon reduction in the presence of the electron carrier, 1-methoxy PMS. The CCK-8 or SK solution is added directly to the cells, no pre-mixing of the components is required. These two kits are sensitive, non-radioactive colourimetric assays for determining the number of viable cells in cell proliferation and Cytoxicity assays. The WST-8 is bio reduced by cellular dehydrogenases to an orange formazan product that is soluble in tissue culture medium. The amount of formazan produced is directly proportional to the number of living cells. Since adherent cells have a higher metabolism than that of leucocyte cells , the O.D. form adherent cells are much larger than leucocyte cells. The detection sensitivity of cell proliferation assays using WST-* are higher than assays using other tetrazolium salts such as MTT, XTT, MTS or WST-1.Since the CCK-8 solution is vert stable and has low toxicity, a longer incubation such as 24 or 48 hours is possible. Because the CCK-8 solution is less toxic, after measurement of cell viability the cells can be used for further studies.
Cell Counting Kit-SK is an alternative kit to CCK-8 for cells with low metabolism as it is more sensitive. CCK-SK enables shorter incubation times to obtain a higher O.D. increase within 30-60 minutes. The assay principle and protocol are the same as for CCK-8.