Brominated pyrrole alkaloids from marine Agelas sponges reduce depolarization-induced cellular calcium elevation.

Seven pyrrole alkaloids isolated from Agelas sponges were tested for interactions with the cellular calcium homeostasis. Brominated pyrrole alkaloids reduced voltage dependent calcium elevation in PC12 cells. Dibromosceptrin was the most potent alkaloid with a half maximal concentration of 2.8 microM followed by sceptrin (67.5 microM) and oroidin (75.8 microM). 4,5-Dibromopyrrole-2-carboxylic acid reduced calcium elevation at concentrations exceeding 30 microM but did not eliminate calcium elevation at concentrations up to 1 mM. 4-Bromopyrrole-2-carboxylic acid and pyrrole-2-carboxylic acid were not active in this respect. The aminoimidazole group appeared to have a significant effect on voltage dependent calcium elevation shown by the comparison of oroidin with 4,5-dibromopyrrole-2-carboxylic acid. The degree of bromination of the pyrrole moiety is another important factor, as was shown by the comparison of 4,5-dibromopyrrole-2-carboxylic acid with 4-bromopyrrole-2-carboxylic acid, as well as oroidin with hymenidin and dibromosceptrin with sceptrin. The previously reported feeding deterrent activity of brominated pyrrole alkaloids in Agelas sponges against predatory reef fish may partly be explained by a general interaction of these alkaloids with the cellular calcium homeostasis. The chemoreception of bromopyrrole alkaloids in sea water is shown using sensory neurons in the rhinophore of the sea slug Aplysia punctata.