Mast Cells and 5-HT: Uptake of labelled 5-hydroxytryptamine (5-HT) and 5-hydroxytryptophan in relation to storage of 5-HT in individual rat mast cells

The capacity of individual rat peritoneal mast cells to take up and concentrate radioactively labelled 5-hydroxytryptamine (5-HT) and 5-hydroxytryptophan (5-HTP) was studied by quantitative cyto-chemical methods. By means of consecutive application of microfluorometric, autoradiographic and microinterferometric methods, the following parameters could be determined for each cell: 1. Relative amount of endogenous 5-HT. 2. Concentration of accumulated isotopes. 3. Dry mass. 4. Concentration of endogenous 5-HT. 5. Total amount of accumulated isotopes. The calculated correlations of these variables to each other showed general heterogeneity of the population, variations between the different cells being very large. However, on the whole, increasing dry mass of the mast cells was accompanied by an increase in 5-HT content, but with a decrease in concentrations of endogenous 5-HT and accumulated radioactive 5-HTP. Similarly, cells having large stores of endogenous 5-HT showed a higher total uptake, but a lower cellular concentration of exogenous 5-HT and 5-HTP, than cells that were poor in endogenous 5-HT. The results indicated that the uptake of ³H-5-HTP was proportional to the total area of the cell membrane, while the degree of 3-HT uptake was determined by other factors. When the concentrations of radioactivity in the incubation medium was compared to that of the living mast cell, it was found that the averagr cell was able to concentrate exogenous 5-HTP and 5-HT around 4 and 30 times, respectively.