Calcium-dependent smooth muscle excitatory effect elicited by the venom of the hydrocoral Millepora complanata
2002; Elsevier BV; Volume: 40; Issue: 6 Linguagem: Inglês
10.1016/s0041-0101(01)00281-1
ISSN1879-3150
AutoresAlejandra Rojas‐Molina, Mónica Torres, Juana-Isela Rojas, Angélica Feregrino, Edgar P. Heimer-de la Cotera,
Tópico(s)Venomous Animal Envenomation and Studies
ResumoIn the present paper, we describe the results obtained from a preliminary pharmacological and biochemical study of the fire coral Millepora complanata, a regular component of coral reefs in the Mexican Caribbean. The protein-containing crude extract obtained from M. complanata (tested from 0.001 to 1000 μg protein/ml) caused a concentration-dependent stimulation of spontaneous contractions of the guinea pig ileum. The extract (EC50=11.55±2.36 μg/ml) was approximately 12-fold less potent than ionomycin (EC50=0.876±0.25 μg/ml) and its maximum induced contraction (1 mg protein/ml) was equivalent to 68% of the response to 60 mM KCl. FPLC size exclusion chromatography of the M. complanta extract afforded 12 primary fractions, of which only FV (containing proteins with molecular weights ranging from 17 to 44 kDa) and FVIII (consisting of peptides with molecular weights lesser than 1.8 kDa) elicited an excitatory effect when tested at the EC50 of the original extract. After incubation in Ca2+-free medium, the ileal response to FV and FVIII was significantly reduced. Blockage of L-type Ca2+ channels with nifedipine (1 μM) inhibited FV and FVIII-evoked contractions. Cd2+ (10 μM), an unspecific blocker of voltage-activated calcium channels, also antagonized FV and FVIII-induced effects, whereas the Na+ channel blocker tetrodotoxin (10 nM) did not significantly affect FV and FVIII responses. These results suggest that the contractions induced by the bioactive fractions obtained from the crude extract of M. complanata are caused mainly by a direct action on smooth muscle cells, via an increase in Ca2+ permeability that occurs, at least partly, through L-type voltage-dependent Ca2+ channels found in the cell membrane of smooth muscle.
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