Inhibition of cromolyn-induced phosphorylation of a 78-kDa protein by phorbol esters in rat peritoneal mast cells.

Disodium cromoglycate (cromolyn) is a well documented inhibitor of immunologically-induced histamine release from rat peritoneal mast cells and has been shown to stimulate the phosphorylation of a mast cell protein of apparent molecular mass 78,000 Da (78 kDa), an event which may be involved in terminating secretion. Here we aimed to determine the role of the ubiquitous enzyme, protein kinase C, in the phosphorylating activity of cromolyn by examining the effects of phorbol esters (activators of protein kinase C) on protein phosphorylation in [32P]orthophosphate loaded rat peritoneal mast cells. Protein kinase C-activating phorbol esters such as 12-O-tetradecanoyl phorbol-13-acetate (TPA) and 4beta-phorbol 12,13-dibutyrate (PdBu) were found to potently inhibit cromolyn-induced phosphorylation when added to mast cells simultaneously with cromolyn (IC50 22 and 79 nM respectively). 4Alpha-phorbol 12,13-didecanoate (PdD), a phorbol ester which does not activate protein kinase C, had no effect on cromolyn-induced phosphorylation. Addition of TPA to mast cells previously exposed to cromolyn for 60 sec (i.e. when 78-kDa protein phosphorylation is maximal) also caused a very rapid dephosphorylation of the 78-kDa protein. Phosphorylation of the 78-kDa protein can also be induced by dibutyryl cyclic GMP and this action was similarly inhibited by TPA and PdBu. Cromolyn inhibited secretion induced by anti-IgE, but not by TPA, and thus inhibition of secretion by cromolyn is further correlated to its phosphorylation of the 78-kDa protein. The data suggest that the inhibitory action of cromolyn on mast cell secretion and phosphorylation of the 78-kDa protein are not mediated through a phorbol ester-sensitive protein kinase C, but more likely that such an enzyme could be involved in regulating dephosphorylation of the 78-kDa protein. Further explanations for this novel dephosphorylating activity of phorbol esters are discussed.

Mechanistic aspects of cromolyn sodium action on the alveolar macrophage: inhibition of stimulation by soluble agonists.

Despite wide use of the drug cromolyn sodium, its mechanism of action remains unknown. The alveolar macrophage plays a major role in the regulation of the inflammatory responses of the lung which may contribute to asthma. Since the biochemical mechanism by which agonists stimulate the alveolar macrophage to produce superoxide anion has been described, the effects of cromolyn sodium on this process were examined. Cromolyn sodium (0.5-4 mM) reversibly blocked macrophage stimulation by formyl peptide and leukotriene B4, but not by phorbol diester and concanavalin A. Cromolyn sodium inhibition was not calcium dependent and could be reversed by increasing the dose of agonist. Cromolyn sodium did not elevate intracellular cAMP, nor did the characteristics of inhibition resemble those observed using cAMP to inhibit agonist stimulation. However, cromolyn sodium did block agonist-mediated stimulation of the phosphatidylinositol (PI) pathway. Taken together, the present results suggest that one site of action of cromolyn sodium may be at the GTP-binding protein of the PI pathway.

Acute chemotic reaction to cromolyn.

Two cases of an acute chemotic reaction of the conjunctiva occurred after the topical administration of cromolyn sodium (cromoglycate disodium). The reaction was not serious for the health or life of the patient but it caused symptoms and signs that might have veen confused with the disease for which the patient was being treated.

The inhibition by dexamethasone and disodium cromoglycate of anaphylactic bronchoconstriction in the rat.

1. A method for the measurement of anaphylactic bronchoconstriction in the rat is described.2. Dexamethasone inhibited this response in a dose-related manner.3. Disodium cromoglycate antagonized the response. A bell-shaped dose-response curve was obtained with peak activity at 1 mg/kg i.v.4. Meclofenamate was not active when given alone or in combination with dexamethasone.5. Methysergide significantly inhibited the response. Mepyramine, atropine, propranolol and adrenalectomy did not significantly modify the response.6. The relationships of anaphylactic bronchoconstriction in the rat to anaphylactic bronchoconstriction in the guinea-pig and to human asthma are discussed.