Sodium fluoride--a stimulus for a calcium-triggered secretory process

Exocytotic enzyme release from rabbit polymorphonuclear leukocytes after treatment with fluoride and calcium

Treatment of rabbit polymorphonuclear leukocytes (PMNs) with 20 mM sodium fluoride for 10 min, followed by removal of fluoride and addition of Ca2+ results in extensive exocytosis. This is apparent from a strong lysozyme release, together with a slight LDH release. During fluoride-activated Ca2+-dependent exocytosis an increase of indo fluorescence and a strong association of 45Ca with the cells occurs. Different inhibitors inhibit both 45Ca association and lysozyme release. Pretreatment of PMNs with pertussis toxin, or the presence of AI3+ in the medium has little effect on fluoride-activated Ca2+-dependent exocytosis. During pretreatment with fluoride, the ATP level strongly decreases. Exocytosis nevertheless occurs upon addition of Ca2+, indicating that a normal ATP level is not required for exocytosis. The glycogen content of the cell strongly decreases during exposure to Ca2+ after pretreatment with fluoride, but not during pretreatment with fluoride. Breakdown of glycogen and accumulation of 3-phosphoglycerate suggest that glycolysis is blocked at the enolase step, but proceeds as far as that step.

Effect of NaF on cAMP accumulation, cAMP-dependent protein kinase activity in, and amylase secretion from, rat parotid gland cells

Stimulation of amylase secretion from parotid glands by beta-adrenergic agonists is mediated by the activation of adenylate cyclase and the resultant increase in cellular cAMP. Since NaF is known to increase adenylate cyclase activity and cAMP accumulation in intact cells, we investigated whether it would stimulate amylase secretion from isolated rat parotid gland cells. The results provide evidence that the addition of NaF (0.01-10 mmol/L) increased cAMP concentration (1.5-2.8-fold) in, and amylase secretion (16-93%) from, isolated parotid gland acinar cells. NaF was found to increase cAMP-dependent protein kinase activity ratios (51-84%) in a concentration- and time-dependent manner. The data suggest that the stimulation of amylase secretion from parotid gland cells by NaF may be mediated by an increase in the cellular cAMP concentration, which exerts its effect, at least in part, by increasing the activity of cAMP-dependent protein kinase.

Histamine-releasing properties of mast cells from various strains of mice

A comparison has been made of the in vitro histamine releasing capacity of peritoneal mast cells from BALB/c, C3H/A, C57BL/6J and CFW mouse strains in response to immunological and non-immunological stimuli namely anti-mouse IgE, Concanavalin A (Con A), ionophore A23187 and sodium fluoride. Anti-IgE-induced histamine secretion was highest in mast cells of CFW mice, intermediate in the cells of C57BL/6J and C3H/A mice and lowest in the cells of BALB/c mice. Similar, although less pronounced, strain-dependent differences were observed in Con A-induced release. Mast cells of C57BL/6J and CFW mice were significantly more sensitive to the action of ionophore A23187 compared to the two other strains, although the cells of each strain responded in different manner. Sodium fluoride-induced histamine release occurred in two ways: from mast cells of BALB/c and C57BL/6J it was dose-dependent at NaF concentrations of 1-15 mM, whereas cells of the two other strains were insensitive to the action of NaF at concentrations of 1-5 mM but at a concentration of 7.5 mM, a very strong potentiation of release was observed. Our results suggest functional heterogeneity of mast cells from various strains of mice, a point to be considered in further studies of mast cell function.

Involvement of guanine nucleotide-binding protein in the gating of Ca2+ by receptors

The introduction of impermeant aqueous solutes into individual cells by microinjection has long been established but the difficulties of manipulating the cytosol composition of large populations of microscopic cells have only recently been overcome. Successful techniques include a dielectric breakdown procedure, treatment with micromolar concentrations of ATP4- (ref. 7) and also with very small (that is nonagglutinating, non-fusogenic) amounts of Sendai virus. So far, attention has been concentrated on the behaviour of the cells (generally their response to applied Ca2+ buffers) at the time when the membrane permeability lesions are open, and thus cytosol and external medium are in contact. I now report a novel technique for monitoring the state of molecular solute permeability in cell membranes and show that the lesions generated by ATP4- in the membrane of mast cells can be closed within seconds of adding Mg2+ so that a cycle of permeabilization and resealing can be used to explore the effect of foreign compounds trapped in the cytosol of effectively intact cells. I show that non-hydrolysable GTP analogues, introduced into the cytosol of mast cells, cause them to undergo exocytotic secretion in response to addition of extracellular Ca2+. This finding is discussed in the light of previous experience relating guanine nucleotide regulatory proteins as intermediaries between receptors and the transducers which they control.

Sodium fluoride evoked histamine release from mast cells. A study of cyclic AMP levels and effects of catecholamines

Calcium triggers the secretion of histamine from mast cells after previous exposure to sodium fluoride. The secretory process can be divided into a fluoride-activation step and a calcium-induced secretory step. It was observed that the fluoride-activation step is accompanied by an elevation of cAMP levels within the cells. The attained high levels of cAMP persist during histamine release. It was further found that catecholamines do not markedly alter the fluoride-induced histamine release. It was also confirmed that the second, but not the first, step in sodium fluoride-induced histamine secretion is inhibited by theophylline.

On the mechanism of histamine release from sodium fluoride-activated mouse mast cells

We have found that sodium fluoride-induced histamine release from mouse mast cells occurs in two separate steps, activation in the presence of fluoride and absence of calcium, and secretion triggered by calcium. The amount of released histamine was dependent either on the time of cell exposure to fluoride or on the final fluoride concentration in the incubation medium. The secretory step depends on the concentration of extracellular calcium; it increased as the concentration of calcium was increased. However, a substantial part of the release was both calcium and energy independent. This part, probably cytotoxic, increased markedly at the highest concentration and with extended times of cell exposure to fluoride. Among other divalent cations tested only strontium could partly substitute calcium to trigger secretion. The activating action of fluoride slowly decayed with time and addition of calcium for up to 2 h caused histamine release. Both steps were dependent on temperature and pH and were inhibited by antimycin A, suggesting that the reaction was enzymatic. The action of fluoride on mouse mast cells closely resembles its action on rat mast cells; however, some differences were also observed.

Cyclic nucleotide involvement in histamine release from mast cells--a reevaluation

Secretory events in cells in general are accompanied by increased levels of cyclic AMP. In mast cells, however, the pattern is reversed. Thus histamine release is associated with a fall in cAMP. It has been suggested that the lowered levels of cAMP lead to an increase in membrane permeability towards calcium and that an influx of such ions triggers the release mechanisms. It has further been reported that high levels of cAMP inhibit histamine release by decreasing the permeability. However, evidence has now accumulated indicating that this general concept is far too simplistic. Studies are reviewed which imply that there is little or no correlation between histamine release and intracellular levels of cyclic nucleotides. A new working hypothesis with respect to the role of these nucleotides in mast cell secretion is proposed.

The influence of hypertonicity on histamine release from isolated rat mast cells

Increasing the tonicity of the incubation medium gradually inhibited histamine release from isolated rat mast cells when induced A-23187, ATP, Thapsigargin, sodium fluoride and compound 48/80 in the presence of extracellular calcium, as well as by the latter in the presence of calcium. In contrast, hypertonicity had but negligible effect on the release caused by the monovalent cation inophore X-537A. The swelling action induced by both ATP and X-537A on rat mast cells was markedly depressed by hypertonicity. Thus, the swelling action seemed to be inherent to the mechanism by which ATP stimulates mast cells to a calcium-dependent histamine secretion, whereas this was not the case with X-537A. For Thapsigargin and sodium fluoride it was demonstrated that only the secretory step, induced by calcium, was inhibited by hypertonicity, and this could be reversed by adjusting the incubation medium to isotonicity. Therefore, the results suggest that the uptake of calcium in the rat mast cells after stimulation is a passive process.

On the mechanism of histamine release induced by thapsigargin from Thapsia garganica L

Thapsigargin (Tg) is a pure chemical compound isolated from Thapsia garganica with a molecular weight of 650. It releases histamine from isolated rat mast cells but not from isolated histamine-retaining mast cell granules. The rate of release is markedly influenced by pretreatment of mast cells with Tg prior to the addition of calcium. In agreement with the effect of the ionophore A23187 but in contrast to many other calcium-dependent histamine-releasing agents, cells preincubated with Tg respond to the secretory action of calcium whenever the ion is introduced. However, after dilution of Tg-pretreated cells histamine release induced by the addition of calcium became dependent on the time of its addition. The secretory reaction induced by Tg and calcium can be divided into a two-step reaction at 37 degrees C. Pretreatment of mass cells with Tg renders the cells insensitive to the secretory action of compound 48/80 in the absence of calcium, and this effect could be partly counteracted if 1 mM of strontium was added together with compound 48/80. It is concluded that among various calcium- and energy-dependent histamine-releasing agents Tg most closely resembles the action of fluoride on isolated rat mast cells.