Valinomycin, a degranulating agent in rat mast cells which inhibits calcium-uptake

Endoplasmic reticulum membrane reorganization is regulated by ionic homeostasis

Recently we described a new, evolutionarily conserved cellular stress response characterized by a reversible reorganization of endoplasmic reticulum (ER) membranes that is distinct from canonical ER stress and the unfolded protein response (UPR). Apogossypol, a putative broad spectrum BCL-2 family antagonist, was the prototype compound used to induce this ER membrane reorganization. Following microarray analysis of cells treated with apogossypol, we used connectivity mapping to identify a wide range of structurally diverse chemicals from different pharmacological classes and established their ability to induce ER membrane reorganization. Such structural diversity suggests that the mechanisms initiating ER membrane reorganization are also diverse and a major objective of the present study was to identify potentially common features of these mechanisms. In order to explore this, we used hierarchical clustering of transcription profiles for a number of chemicals that induce membrane reorganization and discovered two distinct clusters. One cluster contained chemicals with known effects on Ca²⁺ homeostasis. Support for this was provided by the findings that ER membrane reorganization was induced by agents that either deplete ER Ca²⁺ (thapsigargin) or cause an alteration in cellular Ca²⁺ handling (calmodulin antagonists). Furthermore, overexpression of the ER luminal Ca²⁺ sensor, STIM1, also evoked ER membrane reorganization. Although perturbation of Ca²⁺ homeostasis was clearly one mechanism by which some agents induced ER membrane reorganization, influx of extracellular Na⁺ but not Ca²⁺ was required for ER membrane reorganization induced by apogossypol and the related BCL-2 family antagonist, TW37, in both human and yeast cells. Not only is this novel, non-canonical ER stress response evolutionary conserved but so also are aspects of the mechanism of formation of ER membrane aggregates. Thus perturbation of ionic homeostasis is important in the regulation of ER membrane reorganization.

Nonimmunological release of histamine from rat mast cells elicited by antineoplastic agents: effect of drug combinations

We studied the release of histamine elicited by some antineoplastic drugs in rat pleural and peritoneal mast cells. The drugs tested included the antibiotic mitomycin; the anthracyclines daunorubicin, doxorubicin, and epirubicin; the glycopeptide bleomycin; the chromopeptide dactinomycin; the platinum coordination complexes carboplatin and cisplatin; and the anthracenedione mitoxantrone. Mitomycin and bleomycin failed to elicit any release of histamine, whereas all of the other drugs induced histamine release from either pleural or peritoneal mast cells, the release being independent of extracellular calcium. The results indicate that antineoplastic drugs activate histamine release in a manner similar to that shown by compound 48/80, which may contribute to some of their secondary effects.

Dual effect of dihydropyridines on 45Ca uptake induced by the K+ -channel blocker, 4-aminopyridin on mast cells

The 1,4-dihydropyridines (DHP) are calcium antagonists and represent a new class of drugs which act by a selective inhibition of Ca++ influx through voltage-operated calcium channels. We report the effect of nifedipine (Bay A 1040), nisoldipine (Bay K 5552) and nitrendipine (Bay E 5009) on the histamine release and on the 45Ca uptake promoted by 4-aminopyridin in mast cells. These cells treated with DHP (10(-12)-10(-3) M) activated the secretory response in a dose-dependent manner in the range of concentrations 10(-6)-10(-3) M, whereas concentrations of 10(-12)-10(-6) M did not significantly inhibit the secretion. 4-Aminopyridin, a known K+ -channel blocker, induced 45Ca uptake. Pretreatment of mast cells with DHP prior to 4-aminopyridin stimulation inhibited or stimulated 45Ca uptake depending on concentration; thus, concentrations of DHP below 10(-12) of nitrendipine and 10(-9) for nisoldipine and nifedipine were inhibitory, while higher doses potentiated 45Ca uptake. These results demonstrate a diversity of pharmacological effects of DHP on mediator secretion and 45Ca uptake in mast cells and throw into question their only properties as Ca++ antagonists.