THE MARINE NATURAL PRODUCT 3,5-DIBROMO-2-(2,4-DIBROMO-PHENOXY)PHENOL,INHIBITS CONTRACTILE ACTIVITY IN THE GUINEA-PIG ILEUM

1. The tetrabrominated diphenyl ether 3,5-dibromo-2-(2,4-dibromophenox y)phenol (BPE), a natural marine product isolated from a sponge, was t ested for pharmacological activity in guinea-pig ileum. 2. BPE (2 mumo l/L) decreased basal force and the frequency of spontaneous contractio ns of the ileum. It also significantly decreased contractions of the i leum induced by 5 mmol/L barium and to electrical stimulation at param eters which stimulated intrinsic nerves. 3. The slopes of concentratio n-response curves to acetylcholine (ACh), histamine and 5-hydroxytrypt amine (5-HT) were significantly reduced by BPE at concentrations of 2 mumol/L or greater. 4. BPE (2 mumol/L) did not affect calcium-induced contractions of longitudinal muscle fibres from guinea-pig ileum which were stripped of their cellular membrane. It (6 mumol/L) also had no effect on ATP levels in longitudinal muscle fibres. 5. BPE (2 mumol/L) reduced both phasic and tonic components of contractions induced by r aising the extracellular concentration of K+ to 15, 30, 45 or 60 mmol/ L (in the presence of atropine, propranolol, phentolamine and desensi tization to 5-HT to inhibit the effects of nerve transmitter release). 6. BPE (2 mumol/L) reduced carbachol-induced contractions of ileum pr e-incubated in 1 mumol/L felodipine, a blocker of L-type voltage-opera ted calcium channels (VOCC). 7. BPE dose dependently (0.6-6 mumol/L) r educed contractions induced by Ca2+ in both K+ depolarized ileum and i n tissue exposed to carbachol (10 mumol/L) in the presence of felodipi ne (0.1 mumol/L). 8. These results suggest that BPE affects intracellu lar messenger systems controlling cytosolic calcium and/or blocks entr y of calcium into the cell through both VOCC and receptor-operated cha nnels (ROC).