On the interaction in solution of a candidate mucoadhesive polymer, diethylaminoethyl-dextran, with pig gastric mucus glycoprotein.

apparent. Instead we found a broad distribution of fluorescent power. To ascertain the fluorescent power corresponding to one Dil-LDL-receptor complex, we attached labelled LDL particles to a polylysine-coated slide and imaged under identical conditions to the cells. The fluorescent power histogram is shown in Fig. 1( b). The histogram shows a long-tailed distribution; this is at variance with the Poisson distribution assumed by Gross & Webb [4] in their analysis. Electron micrographs, however, of the DiI-LDL showed variability in the particle sizes and a histogram of their corresponding surface areas gave a similar shape to that of Fig. 1( h). This would reasonably suggest that the amount of label incorporated into the lipid shell of an individual LDL particle is dependent on surface area. The data for LDL attached to a polylysine-coated slide can be fitted by a log-normal distribution and the peak position and width obtained used to convolve and fit the cell data. We can quantify the single and double receptors reasonably accurately, but the long tail of this model leads to large errors in the values for cluster sizes of three or more. In view of the inaccuracies involved when using a variably labelled marker such as DiI-LDL to determine cluster sizes, it should be possible instead to use LDL-receptor antibodies labelled with a uniform, unit number of probes to obtain precise values. Further work adopting this approach is envisaged to establish these values.