Studies on Uptake and Decarboxylation of Histidine by Isolated Rat Mast Cells

Isolated rat mast cells, when incubated in a medium containing histidine‐H 3 , took up and decarboxylated histidine, thus forming histamine.Uptake and decarboxylation were measured as a function of incubation time and extracellular histidine concentration.The influence of amino acids, amines, inhibitors of cell metabolism, and inhibitors of histidine decarboxylase was studied on these two processes.It was concluded that at least part of the histidine transport into the cell was mediated by a carrier mechanism.In the presence of the histidine decarboxylase inhibitor NSD‐1055, the amount of histidine accumulated by the cells reached a certain level within 10 min and was not increased significantly by prolonging the incubation time.Histamine‐H 3 formed by the mast cells in vitro from histidine‐H 3 was bound to granules of sonically disintegrated cells, but to a lesser extent than that originally present in the cells.Only a very small proportion of the histidine taken up in the presence of a decarboxylase inhibitor was recovered in the granular fraction.Treatment of mast cells with compound 48/80 released the same relative amounts of the histamine formed in vitro and of that originally present in the cells.