Histidine transport by isolated rat peritoneal mast cells

Histamine content, diamine oxydase and histidine decarboxylase activities along the intestinal tract of the rat

Histamine is widely distributed in the intestine where it is involved in many pathological reactions. The relations between histamine content, diamine oxidase and histidine decarboxylase activity have been investigated along rat's intestine. Results showed significant variations along the intestine. A correlation was observed between histamine and histidine decarboxylase (p less than 0.01), both of them being even in the small intestine (11.8 +/- 2.3 ng/mg ww and 112.5 +/- 21.2 fmoles/hr/mg ww respectively), significantly higher in the caecum (16.3 +/- 1.9 and 178 +/- 20.1) and significantly smaller in the colon (7.3 +/- 1.1 and 65.3 +/- 11.5) than in other intestinal segments. Diamine oxydase activity was higher in ileum (30.7 +/- 7.2 pmoles/min/mg ww) than in jejunum (17.1 +/- 2.8), caecum (4.3 +/- 0.8) and colon (2.6 +/- 2.7), and could not be linked to histamine content. The results fitted in the hypothesis that histamine in rat intestine is mainly located in mast cells where HDC is probably the main enzyme involved in its modulation.

Amine uptake into intact mast cell granules in vitro

Histamine, the principal amine of rat peritoneal mast cells, is taken up into isolated granules with intact membranes. Uptake is pH- and concentration-dependent and is not stimulated by the addition of Mg2+-ATP. The saturable uptake has a Km of 91.1 microM and a Vmax of 95.4 pmol (mg of protein)-1 min-1. Uptake is abolished by 5 mM ammonium ion. 5-HT, the other endogenous amine of the granules, and dopamine and tyramine, which do not occur naturally in rat mast cells, each competitively inhibits [3H]-histamine uptake with Ki's close to 1 microM. Reserpine, a putative amine carrier blocker, inhibits uptake at nanomolar concentrations. At high concentrations, uptake of [3H]-5-HT is nonsaturable; at low concentrations, a saturable component is observed with a Km of 1.6 microM. Uptake of [3H]-5-HT is not enhanced by Mg2+-ATP. It is pH-dependent but with a lower apparent pKa than that of histamine. [3H]-5-HT uptake can be completely inhibited by ammonium ions. Amine inhibition of [3H]-5-HT gives nonlinear Dixon plots, and high concentrations of the competing amines or reserpine cannot completely block uptake. We propose a model consistent with these results in which amine uptake occurs by several distinct saturable transport systems. According to the model, histamine is transported by a single system, which also transports 5-HT and dopamine. 5-HT and dopamine are transported by one or more other systems.

Evidence for rapid histamine turnover and loss of histamine from immature rat mast cells

Histamine synthetic activity which is high in young mast cells decreases as the cells mature [Beaven et al., J. Pharmac. exp. Ther. 224, 620 (1983)]. In this study we show that a substantial proportion of newly formed histamine in young mast cells leaked to the extracellular environment. The cells acquired the full ability to sequester newly formed histamine once the numbers of intracellular granules and the supply of sulfated mucopolysaccharide material within them had increased. Rat peritoneal mast cells were separated into successive fractions of increasing size and maturity by counter current elutriation. Loss of histamine from fractions of immature cells was demonstrated by a progressive accumulation of histamine in the medium without any decrease in intracellular histamine content. The estimated turnover time of histamine was less than 10 hr. In fractions of more mature cells, the proportion of cellular histamine released into the medium was substantially lower, giving estimated turnover times of 20 hr or longer. Studies with radiolabeled histidine also indicated that little, if any, newly formed histamine was lost from fractions of mature cells. Both release of endogenous histamine and formation of radiolabeled histamine from labeled histidine were inhibited by the histidine decarboxylase inhibitor alpha-fluoromethylhistidine (10 microM). Histamine turnover times were similar in the presence or absence of external histidine, a possible indication that the supply of intracellular histidine was sufficient to maintain normal histamine synthetic activity.

Effect on mast cell histamine of inhibiting histamine formation in vivo with alpha-fluoromethylhistidine

An irreversible inhibitor of histidine decarboxylase, alpha-fluoromethylhistidine (FMH), was used to inhibit histamine formation by mast cells in vivo. Even at doses of FMH sufficient to reduce histamine formation more than 95%, the ability of mast cells to synthesize histamine recovered rapidly. It was possible, however, to sustain levels of histamine-forming activity below 10% of normal with continuous administration of FMH from subcutaneously implanted osmotic pumps. Administration of FMH under these conditions did not deplete significantly mast cell histamine but did prevent the increase in total mast cell histamine that occurs over 14 days and also prevented the reconstitution of mast cell histamine stores after depletion by treatment with polymyxin B.

Stimulation by epinephrine of histamine synthesis by rat peritoneal fluid mast cells in vitro

In vitro exposure of mast but not of other cells of rat peritoneal fluid to epinephrine leads, within 1 min, to progressing levels of histamine in both fluid and sedimentable phases of the incubates, which present no increase in their free/total histamine ratio. Histamine increase was blocked by alpha-fluoromethyl histidine (alpha FMH), acting after a significant lag period. When compared with controls under the electron microscope, epinephrine-treated mast cells show less electron-dense, swollen intracellular granules, apparent maintenance of cell membrane continuity and an apparent decrease of peripheral finger-like projections. Histamine accumulation by epinephrine-treated mast cells may be the result of an enhanced ability of pre-formed mast cell histidine decarboxylase to attack its cell-borne substrate, consequent to an unfolding of the cell membrane during cell tumefaction evoked by epinephrine.

Transport of L-histidine by human diploid fibroblasts in culture

The transport of L-histidine has been characterized in skin derived diploid human fibroblasts, cultured under strictly controlled conditions. The transport measurements were made on cells grown to subconfluency after 60 to 90 min timed preincubation. The data, at substrate concentrations ranging from 0.050 to 10 mmol/l, were analyzed by a computer program. A saturable transport system (Km = 0.25 mmol/l, Vmax = 17 nmol/mg protein per min) and a nonsaturable component of influx (Kd = 1.6 +/- 0.4 nmol/mg protein/min per mmol) were found. L-Histidine displayed no Na+ requirement at either low or high concentrations. Inhibition analysis demonstrated that L-histidine uptake at low concentration was poorly inhibited by amino acids known to be effective inhibitors of system A. The largest fraction of L-histidine uptake was inhibited by 2-amino-bicyclo (2,2,1)-heptane-2-carboxylic acid (BCH), leucine, and tryptophan. These results indicated that L-histidine is transported in human fibroblasts mainly by the Na+ independent system L. The differences between this cell type and others studied previously are discussed.

Histidine uptake by isolated rat peritoneal mast cells. Effect of inhibition of histidine decarboxylase by alpha-fluoromethylhistidine

Preincubation with (S)-alpha-fluoromethylhistidine, an irreversible inhibitor of histidine decarboxylase, was found to markedly reduce, but not eliminate, the uptake of [3H]histidine by rat peritoneal mast cells. The Vmax for histidine transport for cells in which decarboxylation of histidine had been completely inhibited was 11.9 pmoles per min per 10(6) cells, compared to a Vmax of 18.9 pmoles per min per 10(6) cells in the presence of active mast cell histidine decarboxylase. The Km of uptake was 139 microM in the presence of alpha-fluoromethylhistidine, several times higher than the Km of 44.0 microM in the uninhibited cell. alpha-Fluoromethylhistidine did not inhibit mast cell uptake of phenylalanine, a competitive inhibitor of histidine uptake but not a substrate for histidine decarboxylase; nor did it inhibit the uptake of histidine by non-mast cells, which lack histidine decarboxylase. Levels of intracellular [3H]histidine in mast cells were similar in the presence and absence of the decarboxylase inhibitor. Based on these observations, we propose that intracellular decarboxylation of histidine in the mast cell serves to specifically enhance the uptake of histidine by the relatively non-specific amino acid transporter present in the plasma membrane of the cell.