Distinct pharmacology of 2-hydroxycarbazole-induced Ca2+ release in the sea urchin egg.
2-hydroxycarbazole, a compound structurally related to the Ca2+-mobilizing marine toxin 9-methyl-7-bromoeudistomin, has recently been proposed to activate both type 1 and type 2 ryanodine receptors in skeletal and cardiac muscle, respectively. This study was undertaken to evaluate the activity of this compound in the sea urchin egg homogenate, a model system used to characterize intracellular Ca2+ mobilization mechanisms. 2-Hydroxycarbazole was found to potently release Ca2+ in a concentration-dependent manner via a specific mechanism displaying apparent desensitization. Use of selective inhibitors of the Ca2+-mobilizing messengers inositol 1,4,5-trisphosphate, cyclic adenosine diphosphate ribose, and nicotinic acid adenine dinucleotide phosphate, as well as desensitization of homogenates to each of these molecules, failed to inhibit the response to 2-hydroxycarbazole. However, the response to 2-hydroxycarbazole was competitively antagonized by caffeine. Investigation of the Ca2+ stores accessed by 2-hydroxycarbazole revealed Ca2+ release from a thapsigargin-insensitive pool. Finally, 2-hydroxycarbazole failed to enhance [3H]ryanodine binding, suggesting the operation of a nonryanodine receptor mechanism. These results demonstrate that 2-hydroxycarbazole is acting to modulate a Ca2+ release mechanism with distinct pharmacological properties to those previously reported in the sea urchin egg.
Thomas
J M
JM
Department of Pharmacology, University of Oxford, Oxford, United Kingdom. justyn.thomas@pharmacology.oxford.ac.uk
Churchill
G C
GC
Patel
S
S
Galione
A
A
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002227:Carbazoles / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D009249:NADP / Q000494:pharmacology; D010063:Ovum / Q000187:drug effects / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism; D012617:Sea Urchins; D019284:Thapsigargin / Q000494:pharmacology
D002227:Carbazoles; D004791:Enzyme Inhibitors; D010726:Phosphodiesterase Inhibitors; D019837:Ryanodine Receptor Calcium Release Channel; D002110:Caffeine; D009249:NADP; D000244:Adenosine Diphosphate; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; C066713:2-hydroxycarbazole; D002118:Calcium