Abstract
BackgroundCompound 48/80 is widely used in animal and tissue models as a “selective” mast cell activator. With this study we demonstrate that compound 48/80 also directly activates enteric neurons and visceral afferents.Methodology/Principal FindingsWe used in vivo recordings from extrinsic intestinal afferents together with Ca++ imaging from primary cultures of DRG and nodose neurons. Enteric neuronal activation was examined by Ca++ and voltage sensitive dye imaging in isolated gut preparations and primary cultures of enteric neurons. Intraluminal application of compound 48/80 evoked marked afferent firing which desensitized on subsequent administration. In egg albumen-sensitized animals, intraluminal antigen evoked a similar pattern of afferent activation which also desensitized on subsequent exposure to antigen. In cross-desensitization experiments prior administration of compound 48/80 failed to influence the mast cell mediated response. Application of 1 and 10 µg/ml compound 48/80 evoked spike discharge and Ca++ transients in enteric neurons. The same nerve activating effect was observed in primary cultures of DRG and nodose ganglion cells. Enteric neuron cultures were devoid of mast cells confirmed by negative staining for c-kit or toluidine blue. In addition, in cultured enteric neurons the excitatory action of compound 48/80 was preserved in the presence of histamine H1 and H2 antagonists. The mast cell stabilizer cromolyn attenuated compound 48/80 and nicotine evoked Ca++ transients in mast cell-free enteric neuron cultures.Conclusions/SignificanceThe results showed direct excitatory action of compound 48/80 on enteric neurons and visceral afferents. Therefore, functional changes measured in tissue or animal models may involve a mast cell independent effect of compound 48/80 and cromolyn.
Highlights
Mast cells play a fundamental role for physiological as well as pathological functions [1], [2]
Effects of Compound 48/80 in vivo Compound 48/80 applied intraluminally evoked a marked increase in discharge after a mean latency of 54 s which recovered towards baseline after about 1 min (Figure 1A)
We could only identify three studies which confirmed this mode of action in isolated mast cells; these studies demonstrated that compound 48/80 degranulates mast cells and that this effect is reversed by mast cell stabilizers [23,24,25]
Summary
Mast cells play a fundamental role for physiological as well as pathological functions [1], [2]. They contain a plethora of bioactive mediators which are released upon IgE-directed and non-IgE-directed stimulation. Compound 48/80 is a mixed polymer of p-methoxy-N-methyl phenylethylamine crosslinked by formaldehyde and widely used for non-IgE dependent stimulation of mast cells. It was first characterized as a histamine releaser in 1951 [3]. With this study we demonstrate that compound 48/80 directly activates enteric neurons and visceral afferents
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