Transmembrane sodium and potassium gradients modulate histamine secretion induced by ionophore A23187

The effect of Na+-K+ ATPase inhibition by ouabain on histamine release from human cutaneous mast cells

BACKGROUND

There are controversial reports on the effect of sodium-potassium adenosine triphosphatase (Na+-K+ ATPase) inhibition on mast cell mediator release. Some of them have indicated that ouabain (strophanthin G), a specific Na+-K+ ATPase inhibitor, inhibited the release, whereas the others have shown that ouabain had no effect or even had a stimulatory effect on the mediator secretion. Most of these studies have utilized animal-derived mast cells. The aim of this study was to determine the effect of Na+-K+ ATPase inhibition on human skin mast cells.

METHODS

Unpurified and purified mast cells were obtained from newborn foreskins and stimulated by calcium ionophore A23187 (1 microM) for 30 min following a 1 hr incubation with various concentrations (10(-4) to 10(-8) M) of ouabain. Histamine release was assayed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The results indicated that ouabain had no significant effect on the non-immunologic histamine release from human skin mast cells, in vitro.

CONCLUSIONS

Na+-K+ ATPase inhibition by ouabain had no significant effect on the non-immunologic histamine release from human cutaneous mast cells and suggested differences between human and animal mast cells.

Ouabain-induced enhancement of rat mast cells response. Modulation by protein phosphorylation and intracellular pH

The digitalic glicoside ouabain induces potentiation of rat mast cell histamine release in response to several stimuli, which is mediated by Na+/Ca2+ exchanger. In this work, we studied the effect of ouabain on cytosolic calcium, intracellular pH and histamine release with Ca2+ ionophore A23187 in conditions designed to maximize ouabain-induced potentiation of rat mast cells response. The effect of protein kinase C (PKC), cAMP and phosphatase inhibition was also tested. Ouabain induced an enhancement in histamine release, cytosolic calcium and intracellular pH. The adenylate cyclase activator forskolin reduced the effect of ouabain on histamine release and intracellular pH, but enhanced the effect on cytosolic calcium. PKC activator PMA enhanced the effect of ouabain on histamine release and cytosolic calcium, without affecting intracellular pH. A PKC inhibitor, GF-109203X, reduced ouabain-induced enhancement of histamine release and intracellular pH, but increased the enhancement on cytosolic calcium. Finally, inhibition of protein phosphatases 1 and 2A with okadaic acid, increased the effect of ouabain on histamine release and intracellular pH, but reduced cytosolic calcium in presence of ouabain. This result suggest that ouabain-induced potentiation of rat mast cell histamine release with A23187 is modulated by kinases, and this modulation may be carried out by changes in intracellular alkalinization. However, the mechanism underlying cellular alkalinization remains to be elucidated.

Inhibition of the sodium, potassium adenosine triphosphatase enzyme in peripheral blood mononuclear cells of subjects with allergic rhinitis

BACKGROUND

Previous investigations have documented that a sodium, potassium adenosine triphosphatase (Na+,K+ ATPase) enzyme inhibitor is bound to the platelet membrane, displaced from the platelet membrane by freezing, and present in the plasma of subjects with allergic rhinitis. Others have shown that stimulation of Na+,K+ ATPase is an important early event in mitogen-induced activation of peripheral blood mononuclear cells.

OBJECTIVE

The purpose of this study was to determine whether the Na+,K+ ATPase enzyme inhibition observed in the platelets of subjects with allergic rhinitis also extends to peripheral blood mononuclear cells.

METHODS

Na+,K+ ATPase activity of a particulate fraction of sonicated peripheral blood mononuclear cells was determined by spectrophotometry in asymptomatic adults with and without allergic rhinitis.

RESULTS

The mean Na+,K+ ATPase activity of peripheral blood mononuclear cells expressed as nanomoles per microgram protein per minute (nM/ microgram protein/ min) +/-1 standard deviation of the subjects with allergic rhinitis (n = 14) was 1.04 +/- 1.01, while that of the control subjects (n = 12) was 3.57 +/- 1.60 (P < or = .001). In contrast, when the peripheral blood mononuclear cell membranes were frozen and then thawed prior to assay, the mean Na+,K+ ATPase activity for the subjects with allergic rhinitis (n = 24) was 5.33 +/- 2.62, while that of the control subjects (n = 23) was 1.12 +/- 1.24 (P < or = .001). Samples from a subset of subjects (n = 5) were assayed for both pre-freezing and post-freezing Na+,K+ ATPase activity. The freezing process was associated with a striking increase in Na+,K+ ATPase levels of subjects with allergic rhinitis (4.42 +/- 2.06) but a decrease in those of the control subjects (-3.89 +/- 0.95; P < or = .001).

CONCLUSIONS

These data demonstrate that peripheral blood mononuclear cells from subjects with allergic rhinitis, like platelets, possess a membrane-bound Na+,K+ ATPase inhibitor that is displaced from the membrane by freezing. In vivo Na+,K+ ATPase inhibition could have significant effects on the activation and function of peripheral blood mononuclear cells in subjects with allergic rhinitis.

Mast cell activation involves plasma membrane potential- and thapsigargin-sensitive intracellular calcium pools

The regulation and role of the intracellular Ca2+ pools were studied in rat peritoneal mast cells. Cytosolic free calcium concentration ([Ca2+]i) was monitored in fura-2 loaded mast cells. In the presence of Ca2+ and K+, compound 48/80 induced a biphasic increase in [Ca2+]i composed of a fast transient phase and an apparent sustained phase. The sustained phase was partially inhibited by the addition of Mn2+. DTPA, a cell-impermeant chelator of Mn2+, reversed this inhibition, suggesting that a quenching of fura-2 fluorescence occurs in the extracellular medium. In the absence of extracellular Ca2+, the transient phase, but not the sustained one, could be preserved, provided that mast cells were depolarized. The transient phase was completely abolished by thapsigargin, a microsomal Ca(2+)-ATPase inhibitor. Maximum histamine release induced by either compound 48/80 or antigen was obtained in the absence of added Ca2+ only when mast cells were depolarized. These histamine releases were inhibited by low doses (< 30 nM) of thapsigargin. Thapsigargin at higher doses induced histamine release which was unaffected by changing the plasma membrane potential, but was completely dependent on extracellular Ca2+, showing that a Ca2+ influx is required for thapsigargin-induced exocytosis. Together, these results suggest that the mobilization of Ca2+ from thapsigargin sensitive-intracellular pools induced by compound 48/80 or antigen is sufficient to trigger histamine release. The modulation of these pools by the plasma membrane potential suggest their localization is close to the plasma membrane.

Ca(2+)-activated outward-rectifier K+ channels and histamine release by rat gastric enterochromaffin-like cells

Gastric enterochromaffin-like (ECL) cells were isolated from rat gastric fundic mucosa by Percoll density-gradient centrifugation and counter-flow elutriation. About 67% of cells in the purified cell suspension were ECL cells, which were reacted with anti-histidine decarboxylase antibody. A23187, a calcium ionophore, at 0.1-10 microM induced histamine release from ECL cell-rich suspension, indicating that the Ca2+ pathway is involved in the mechanism of histamine release from the ECL cells. A23187 at 5 microM significantly increased outward-rectifier cationic current in 62% of cells in the ECL cell-rich factions. A23187-sensitive cells showed acridine orange uptake. In single-channel recordings, a Ca(2+)-dependent outward-rectifier K+ channel of large conductance (146 +/- 22 picosiemens) was found in the cell that showed acridine orange uptake. The channel opened in a voltage-dependent manner at 0.1 microM of intracellular free Ca2+ concentration. These results may suggest that opening of the Ca(2+)-activated K+ channel is one of the steps involved in the mechanism of histamine release in ECL cells.

Peptidergic pathway in human skin and rat peritoneal mast cell activation

The common pathway of heterogenous mast cell activation as mediated by antigens is through the cross-linking of IgE bound to Fc epsilon RI receptors. The peptidergic pathway of mast cell activation, achieved by cationic secretagogues, is restricted to "serosal" mast cells, the experimental models being rat peritoneal and human skin mast cells. Cationic secretagogues include positively charged peptides but also various amines such as compound 48/80 and natural polyamines. An early intracellular event of this pathway is the activation of pertussis toxin-sensitive G proteins. The correlation observed between the ability of basic compounds to trigger mast cell exocytosis and their potency to activate purified G proteins strongly suggests that cationic compounds activate mast cell G proteins via a receptor-independent but membrane-assisted process. In this paper, alternative mechanisms are discussed. The consequence of G protein stimulation is the activation of phospholipase C with an increase in inositol triphosphates. Natural polyamines are relatively poor triggers of mast cells (10(-4) to 10(-2) M). Neuropeptides such as substance P, neuropeptide Y or vasoactive intestinal peptide, peptidic hormones such as kinins, and venoms such as mastoparan and mast cell degranulating peptide, are all active in a concentration range from 10(-7) to 10(-4) M. The cationic anaphylatoxin C3a also stimulates mast cells at concentrations below precursor complement C3 blood levels. The component C3 of the complement system is one of only a few plasma proteins having activation fragments (i.e. C3a) that can be generated at micromolar levels. The effects of basic secretagogues defines a peptidergic pathway of mast cell activation, which represents a potentially toxic process considering the tissue effects caused by exogenous basic compounds such as venom peptides and certain amine containing drugs. Peptidergic activation of mast cells may also be a pathophysiological process having an important role in neurogenic inflammation and in diseases involving extensive activation of the blood complement cascade.

The use of the potential-sensitive fluorescent probe bisoxonol in mast cells

The regulation of the plasma membrane potential of rat peritoneal mast cells at the resting state and during activation was investigated using bisoxonol as a potential-sensitive fluorescent dye. Fluorescence microphotography showed that this negatively charged probe was not only present in the plasma membrane, but was also distributed in the cytoplasm. The intracellular localization of bisoxonol was confirmed by conducting experiments which showed that bisoxonol fluorescence was not enhanced in ATP-permeabilized mast cells. Rotenone (10(-7) M) and oligomycin (10(-6) M) did not change the fluorescence of bisoxonol showing, therefore, mitochondrial depolarization was not recorded with bisoxonol and suggesting that bisoxonol may represent a useful probe to study plasma membrane potential changes in the absence of exocytosis. We showed that, in non-stimulated mast cells, the blockade of the sodium pump enhanced the fluorescence of bisoxonol as did gramicidin a non selective ionophore used to fully depolarize the cells. High concentration of potassium (30 mM) as well as different ionic channel blockers did not significantly change the fluorescence intensity of bisoxonol, suggesting that ionic channel permeabilities were not involved in maintaining the resting plasma membrane potential of mast cells. Mast cells stimulated by compound 48/80 completely lost the fluorescence, shown by fluorescence microphotography, suggesting that exocytotic phenomena might induce a dye redistribution which is not only due to changes in the plasma membrane potential. In mast cells pretreated with pertussis toxin, which blocks mast cell-exocytosis, compound 48/80 induced a delayed (2 min) decrease of bisoxonol fluorescence which was shown to be dependent on the activity of the sodium pump. Considering that bisoxonol is a useful potential-sensitive probe in exocytosis-deprived mast cells, our results suggest that the sodium pump is mainly involved in the changes of plasma membrane potential of mast cells.

Regulation of the Na(+)-K+ pump activity and estimation of the reserve capacity in intact rat peritoneal mast cells

Evidence is provided that regulation of the Na(+)-K+ pump activity in rat peritoneal mast cells occurs mainly through stimulation of the pump from inside the plasma membrane by sodium. It is demonstrated that there is a large reserve capacity for the exchange of intracellular sodium with extracellular potassium in these cells. The maximal pump activity was estimated to be 3230 pmol/10(6) cells per min and Km for extracellular potassium was 1.5 mM.

Inhibition of Na(+) -K+ pump activity by divalent cations in intact peritoneal mast cells of the rat

1. The inhibition by the divalent cations magnesium, barium and strontium and the trivalent ion lanthanum of the Na(+) -K+ pump in the plasma membrane of rat peritoneal mast cells was studied in pure mast cell populations by measurement of the ouabain-sensitive uptake of the radioactive potassium analogue, 86rubidium (86Rb+). 2. Exposure of the cells to magnesium induced a time- and concentration-dependent decrease in the ouabain-sensitive K+(86Rb+)-uptake of the cells without influencing the ouabain-resistant uptake. The time-dependent decrease was apparent after incubation of the cells for 10 min or more, but no decrease was observed after 2 min incubation when the cells are supposed to be loaded with sodium due to the cell isolation procedure. 3. Barium and strontium caused concentration-dependent decreases in the ouabain-sensitive K(+) -(86Rb+) -uptake of the cells but the ouabain-resistant uptake was not changed. Half maximum decrease in the ouabain-sensitive K+(86Rb+)-uptake was observed with 1.8 mM magnesium, 1.2mM barium and 0.7 mM strontium. 4. The trivalent ion lanthanum blocked almost completely the ouabain-sensitive K+(86Rb+)-uptake at a concentration of 1 microM as does 1 mM calcium. Combining either of these ions with magnesium had no further inhibitory effect on the ouabain-sensitive uptake. 5. In conclusion, in addition to the previously suggested modulation by calcium of the activity of the Na+ (-)K+ pump, evidence is provided in this investigation that the modulation may be a more general effect of divalent and polyvalent cations present in the extracellular space through their influence on the sodium permeability of the plasma membrane.

Reversal by EGTA of the enhanced secretory responsiveness of mast cells due to treatment with ouabain

The effect of EGTA on the enhancement by ouabain of compound 48/80-induced secretion from mast cells was compared with the effect on the Na(+)-K+ pump activity. The time-dependent secretory enhancement by ouabain was blocked by addition of EGTA to the cell suspension concomitantly with the addition of ouabain, and EGTA caused a large increase in the pump activity. Addition of 10 microM EGTA to ouabain-treated cells stopped but did not reverse the enhancement. The experiments show that the effect of ouabain was due to changes in a calcium pool utilized in compound 48/80-induced secretion following changes in the Na+,K+ pump activity.

The mode of inhibition of the Na+-K+ pump activity in mast cells by calcium

1 The inhibition by calcium of the Na(+)-K+ pump in the plasma membrane of rat peritoneal mast cells was studied in pure populations of the cells by measuring the ouabain-sensitive uptake of the radioactive potassium analogue, 86rubidium (86Rb+). 2 Exposure of the cells to calcium induced a time- and concentration-dependent decrease in the ouabain-sensitive K+(86Rb+)-uptake of the cells without influencing the ouabain-resistant uptake. The development of the inhibition required the presence of potassium in the medium in the millimolar range (1.5-8.0 mM), and it did not occur at a concentration of potassium (0.24 mM) that is probably rate limiting for the pump activity. In the presence of 1 mM calcium full inhibition developed almost immediately and was not readily reversed. The inhibition was not significantly reduced by 15 min incubation with 1.2 mM EGTA. 3 The inhibitory action of calcium did not develop when the mast cells were incubated in a potassium-free medium, which is known to block Na(+)-K+ pump activity and allow accumulation of sodium inside the cells. Likewise, increasing the sodium permeability of the plasma membrane by monensin abolished the inhibition of the pump activity. In both cases, incubation of the cells with 4.7 mM potassium and tracer amounts of 86Rb+ resulted in a very large uptake of K+ (86Rb+) into the cells (up to 2 nmol per 10(6) cells min-1), indicating a high activity of the Na(+)-K+ pump. 4. These observations support the view that long-term incubation of rat peritoneal mast cells in a calcium-free medium increases the permeability of the plasma membrane to sodium, and the consequent increase in the intracellular concentration of sodium causes an increase in the activity of the pump. Addition of calcium to the cell suspension decreases the sodium permeability, and hence the pump activity. This hypothesis is supported by the stimulation of pump activity produced by monensin, which is not inhibited by calcium. The enhancement of pump activity after exposure of calcium-deprived cells to EGTA might be the result of a further increase in the sodium permeability of the plasma membrane.

Na+ -K+ pump activity in rat peritoneal mast cells: inhibition by extracellular calcium

1. Pure populations of rat peritoneal mast cells were used to study cellular potassium uptake. The radioactive potassium analogue, 86rubidium, was used as a tracer for potassium for measurements of the activity of the cellular potassium uptake process. 2. The ouabain-sensitive and the ouabain-resistant potassium (86rubidium) uptake of mast cells incubated in the presence of calcium, 1 mmol l-1, were very low, 52 and 147 pmol per 10(6) cells min-1. 3. Calcium-deprivation of the cells uncovered a large capacity ouabain-sensitive potassium (86rubidium) uptake mechanism. The activity of the uptake mechanism was decreased by reintroduction of calcium into the cell suspension, and it was dependent on cellular energy metabolism, temperature and pH. 4. The potassium (86rubidium) uptake of mast cells incubated in a calcium-free medium occurs through an active and ouabain-sensitive mechanism that has the nature of an enzyme, and it is mediated by the Na+ -K+ pump located in the plasma membrane. It is demonstrated that the activity of the Na+ -K+ pump mechanism is inhibited by low concentrations of extracellular calcium (0.1-1.2 mmol l-1). The possibility is discussed that calcium-deprivation may increase the pump activity by increasing the permeability of the plasma membrane for Na+.

Preservation of the secretory response of peritoneal mast cells in the absence of extracellular calcium

The transfer of rat peritoneal mast cells from balanced salt solution to calcium-free buffer led to a time-dependent decrease in their response to compound 48/80 and to ionophore A23187. The concomittant absence of potassium from the calcium-free buffer enabled the mast cells to retain their secretory response. The increase in potassium level, with a parallel decrease in sodium to maintain osmolarity, led to a slight potentiation of the response to 48/80 and to a large but transient potentiation of the response to A23187. Mast cells can be considered nonexcitable. The apparent dependency upon extracellular calcium of mast cell secretory responses might be related to the presumed tight equilibrium between endoplasmic reticulum calcium stores and extracellular calcium. The control of this equilibrium by transmembrane gradients of monovalent ions is proposed.