Histamine release by compound 48/80: evidence for the depletion and repletion of calcium using chlortetracycline and 45calcium

Mast cell degranulation breaks peripheral tolerance

Mast cells (MC) have been shown to mediate regulatory T-cell (T(reg))-dependent, peripheral allograft tolerance in both skin and cardiac transplants. Furthermore, T(reg) have been implicated in mitigating IgE-mediated MC degranulation, establishing a dynamic, reciprocal relationship between MC and T(reg) in controlling inflammation. In an allograft tolerance model, it is now shown that intragraft or systemic MC degranulation results in the transient loss of T(reg) suppressor activities with the acute, T-cell dependent rejection of established, tolerant allografts. Upon degranulation, MC mediators can be found in the skin, T(reg) rapidly leave the graft, MC accumulate in the regional lymph node and the T(reg) are impaired in the expression of suppressor molecules. Such a dramatic reversal of T(reg) function and tissue distribution by MC degranulation underscores how allergy may causes the transient breakdown of peripheral tolerance and episodes of acute T-cell inflammation.

Ionomycin and 2,5'-di(tertbutyl)-1,4,-benzohydroquinone elicit Ca2+-induced Ca2+ release from intracellular pools in Physarum polycephalum

Calcium level in organelles of the slime mold Physarum polycephalum was monitored by chlortetracycline, a low-affinity calcium indicator. It was found that 2,5'-di(tertbutyl)-1,4,-benzohydroquinone (BHQ) at a concentration of 100 microM, but not the highly specific inhibitor of sarco-endoplasmic reticulum Ca2+-ATPase (SERCA), thapsigargin (1-10 microM), elicited calcium release from the CTC-stained intracellular calcium pool. Ionomycin also caused a calcium release (23.7+/-5.1%), which was less than that induced by BHQ (30.1+/-6.0%). Procaine (10 mM), a blocker of ryanodine receptor, completely abolished the responses to BHQ and ionomycin. Another blocker, ryanodine (100 microM), only slightly diminished the responses to ionomycin and BHQ. Apparently, BHQ and ionomycin acting as a Ca2+-ATPase inhibitor and an ionophore, respectively, elicit an increase in [Ca2+]i, which in turn triggers a calcium-induced calcium release (CICR) via the ryanodine receptor. Caffeine, an activator of ryanodine receptor, at a concentration of 25-50 mM produced a Ca2+-release (5.6-16.0%), which was not similar in magnitude to CICR. The response to 25 mM caffeine was only moderately inhibited by 25 mM procaine, and almost completely abolished by 50 mM procaine and 100 microM ryanodine.

Histamine release from rat mast cells induced by econazole

1. Econazole released histamine from rat mast cells in vitro. This response was not affected by the addition of calcium or by prior treatment of mast cells with EDTA or cromoglycate. 2. Rat mast cells treated with econazole were stained by the vital dye trypan blue. 3. The intradermal injection of econazole increased vascular permeability. This response was antagonized by chlorpheniramine and cyproheptadine. 4. Our results demonstrate that econazole releases histamine by the "nonselective" mechanism. It is suggested that econazole inflammatory effects may be due to histamine release from mast cells.

Replenishment of the cellular calcium required for non-immunologic stimulation of mast cell histamine secretion: temperature sensitivity and inhibition by manganese and sodium-free conditions

Mast cells depleted of cellular calcium (Ca) by a 3 hr exposure to Ca-free conditions and then bathed in Ca-free Locke failed to release histamine when stimulated by compound 48/80 or peptides. The cellular Ca required for histamine release could be replenished by a 5 sec exposure to extracellular Ca at 37 degrees C. To inhibit this replenished cellular Ca dependent histamine secretion required an additional 3 hr exposure to Ca-free conditions. When cellular Ca was replenished at 4 degrees C, an additional 2 min incubation at 37 degrees C was required to restore stimulated secretion to a maximum. During this 2 min incubation period the replenished cellular Ca is suggested to be "processed" so that it can be used for secretion. Manganese (Mn) or cobalt added during (but not after) this 2 min incubation period prevented the restoration of histamine release. Preincubation of cellular Ca depleted mast cells in Mn (0.1-1 mM) blocked the effect of subsequent Ca replenishment at 37 degrees C while cobalt and barium were less inhibitory. Neither magnesium nor strontium were inhibitory. Extracellular sodium (Na) was required for the restoration of cellular Ca dependent histamine secretion. Lithium could substitute for Na but rubidium and potassium were ineffective.

The role of a Ca2+/calmodulin dependent plasma membrane Ca2+ channel during concanavalin A activation of MC9 mast cells

The effects of Con A on free cytoplasmic calcium concentrations in the cloned murine mast cell, MC9, have been measured using the fluorescent calcium indicator quin 2. Con A causes a rapid, small yet sustained rise in free cytosolic calcium (up to 245 nM) followed closely by increased 45calcium uptake and more slowly by histamine release. The increases in 45calcium uptake and histamine release require extracellular calcium. However, the Ca2+ influx blockers, nifedipine and verapamil inhibit these responses only at concentrations significantly higher than those used in smooth muscle to oppose potential-dependent events, and diltiazem is inactive. These observations suggest that, in these mast cells, other types of channels control Ca2+ entry. In contrast, the intracellular Ca2+ blocker, TMB-8, inhibits both the Con A-induced histamine release and the Ca2+ changes. The calmodulin antagonists calmidazolium, trifluoperazine and W-7 are also highly effective inhibitors of both the Ca2+ changes and histamine release in direct proportion to their potency against calmodulin-dependent phosphodiesterase, implicating calmodulin in the regulation of stimulus-secretion in MC9 cells. These data imply that histamine release follows increases in intracellular Ca2+ concentration. Free intracellular Ca2+ results from rapid release from internal stores and is followed by a slower but more sustained influx of extracellular Ca2+.

Lack of specificity of melittin as a probe for insulin release mediated by endogenous phospholipase A2 or lipoxygenase

The effects of the basic polypeptide melittin on islet phospholipid degradation and insulin release were studied in static incubations of intact rat islets as a possible model of endogenous phospholipase A2 (PLA2) activation. Melittin (2 micrograms/ml) increased [3H]-arachidonic acid [( 3H]-AA) release from prelabeled islets (at 1.7 mM glucose) to 371% of basal values. Concomitantly, melittin induced degradation of islet phospholipids labeled with [3H]-AA or [14C]-stearic acid, and led to the accumulation of stearate-labeled (but not AA-labeled) lysophosphatidylcholine (LPC, 605% of control). These findings suggested, for the first time in intact rat islets, the presence and activation of a PLA2. Under identical conditions, melittin initiated insulin secretion (at 1.7 mM glucose) in a manner that represented stimulation of physiologic exocytosis--that is, it was dose-dependent, reversible (albeit slowly), unassociated with impairment of other physiologic islet processes (i.e. the response to 16.7 mM glucose after removal of the drug) and inhibitable by reduced ambient temperature. The effect of melittin seemed to be independent of extracellular Ca2+ influx or mobilization of intracellular Ca2+ stores but was blocked by nickel or lanthanum, indirectly suggesting that the effects of this cationic amphiphile might involve a superficial pool of Ca2+. Unexpectedly, melittin-induced insulin release (at least at low glucose concentrations) was not greatly or consistently altered by a battery of inhibitors of endogenous PLA2 or of enzymes affecting AA oxygenation. Furthermore, significant contamination by bee venom PLA2 of the commercially-available melittin preparation was found, and insulin release could be induced by pure bee venom PLA2, probably through the generation of lysophospholipids. Although estimates of the amount of PLA2 in the melittin preparation suggested that such contamination was insufficient to explain at least some of the islet phospholipid hydrolysis and insulin release caused by melittin, we conclude that this agent does not serve as a specific probe of the role of endogenous PLA2 or of AA lipoxygenation in hormone release.