A cytofluorometric and radiochemical analysis of the uptake and turnover of 5-hydroxytryptamine in mast cells.

Uptake and turnover of 5-hydroxytryptamine (5-HT) after the administration of 5-hydroxytryptophan (5-HTP) has been studied in rat peritoneal mast cells using radiochemical and quantitative cytofluorometric methods. There was a close agreement between the results obtained with the two methods. The extreme sensitivity of the cytofluorometric method was indicated by the fact that 0.2 pg 5-HT contained in mast cells from control rats could be readily quantitated. The cytofluorometric analysis demonstrated a large variation in 5-HT content of individual mast cells within the mast cell populations. The storage capacity for 5-HT greatly exceeded the amount found in normal mast cells. Intraperitoncally injected 5-HTP was rapidly taken up and eliminated from the mast cells within 12 hr, while 5-HT, probably derived from intracellular decarboxylation of 5-HTP, was retained in the cells and slowly eliminated. The elimination of 5-HT followed an exponential course and the half-life was found to be about 10 days. The results indicate that the turnover of 5-HT is much slower in mast cells than in other cells which normally store 5-HT.