The application of Poisson units to the determination of median lethal cell culture dose.

The median lethal cell culture dose (CCLD(50)) and its 95% confidence interval were determined using the Behrens and Kärber area method with subsequent regression analysis by the action of methylmercury iodide (CH(3)HgI; MMI) on monolayer cultures of HeLa cells. The concentrations of MMI were 0.45, 0.9, 1.8, 3.65, 7.3 and 14.6 microM/l. The duration of MMI action was 24 h. All the calculations were performed with means of sample cell numbers derived from Poisson units. The basis for deriving the Poisson units is the Poisson distribution property on the equality mean to variance or, which is the same, on the equality standard deviation to the root square of mean. Because the size of Poisson unit is predetermined, it is a simple task to find the mean. The outcome of any single count of discrete random objects in the definite area or time interval is divided by the number of Poisson units. The Poisson unit for counting cultured cells was derived by us in relation to Gorjaev's net. In this case it is appropriate to count the cells on the square equal to two Gorjaev's nets. The corresponding Poisson unit is equal to 1/5 of Gorjaev's net (45 big squares). Near-coincidence of CCLD(50) as well as its 95% confidence intervals by use of logarithmic and linear models was observed. However, the former approach was better than the second. CCLD(50) and its 95% confidence interval values, obtained with the aid of the logarithmic model in three series of experiments, were 2.56+/-0.33, 2.09+/-0.37 and 2.31+/-0.37 microM/l.