Abstract

Rat basophil leukemia (2H3) cells, like normal rat peritoneal mast cells, were shown to take up and decarboxylate histidine. Uptake was mediated by a temperature-dependent system with high affinity (apparent Km 24 +/- 4 microM) for histidine. Newly formed histamine was incorporated into the intracellular pool of histamine. In confluent cultures, substantial amounts of histamine were lost to the medium while intracellular histamine levels remained constant. As calculated from the rate of appearance of histamine in the medium, the maximum turnover time for the intracellular histamine pool (2-7 nmol/10(6) cells) was about 12 hr. Variation in histamine content, histidine uptake and histidine decarboxylation was noted with different passages of 2H3 cells, but with all passages there were characteristic changes in these parameters during growth and division of the cells. Separation of cells into fractions of different size by elutriation indicated low rates of histidine uptake and decarboxylation in the smallest 2H3 cells, a progressive increase in ability to take up and decarboxylate histidine as the cells approached the S phase of growth and marked decline in this ability in fractions containing the larger cells. The changes in kinetic constants suggested that fluctuation in histidine uptake during the life cycle of the 2H3 cell was due to changes in the number of active carriers or sites of histidine transport and that during cell division all components associated with histamine synthesis (i.e., histidine uptake and decarboxylation) were diminished.