Otilonium: a potent blocker of neuronal nicotinic ACh receptors in bovine chromaffin cells.
1. Otilonium, a clinically useful spasmolytic, behaves as a potent blocker of neuronal nicotinic acetylcholine receptors (AChR) as well as a mild wide-spectrum Ca2+ channel blocker in bovine adrenal chromaffin cells. 2. 45Ca2+ uptake into chromaffin cells stimulated with high K+ (70 mM, 1 min) was blocked by otilonium with an IC50 of 7.6 microM. The drug inhibited the 45Ca2+ uptake stimulated by the nicotinic AChR agonist, dimethylphenylpiperazinium (DMPP) with a 79 fold higher potency (IC50 = 0.096 microM). 3. Whole-cell Ba2+ currents (IBa) through Ca2+ channels of voltage-clamped chromaffin cells were blocked by otilonium with an IC50 of 6.4 microM, very close to that of K(+)-evoked 45Ca2+ uptake. Blockade developed in 10-20 s, almost as a single step and was rapidly and almost fully reversible. 4. Whole-cell nicotinic AChR-mediated currents (250 ms pulses of 100 microM DMPP) applied at 30 s intervals were blocked by otilonium in a concentration-dependent manner, showing an IC50 of 0.36 microM. Blockade was induced in a step-wise manner. Wash out of otilonium allowed a slow recovery of the current, also in discrete steps. 5. In experiments with recordings in the same cells of whole-cell IDMPP, Na+ currents (INa) and Ca2+ currents (ICa), 1 microM otilonium blocked 87% IDMPP, 7% INa and 13% ICa. 6. Otilonium inhibited the K(+)-evoked catecholamine secretory response of superfused bovine chromaffin cells with an IC50 of 10 microM, very close to the IC50 for blockade of K(+)-induced 45Ca2+ uptake and IBa. 7. Otilonium inhibited the secretory responses induced by 10 s pulses of 50 microM DMPP with an IC50 of 7.4 nM. Hexamethonium blocked the DMPP-evoked responses with an IC50 of 29.8 microM, 4,000 fold higher than that of otilonium. 8. In conclusion, otilonium is a potent blocker of nicotinic AChR-mediated responses. The drugs also blocked various subtypes of neuronal voltage-dependent Ca2+ channels at a considerably lower potency. Na+ channels were unaffected by otilonium. This extraordinary potency of otilonium in blocking nicotinic AChR, unrecognised until now, might account in part for its well known spasmolytic effects.
Gandía
L
L
Departamento de Farmacología, Universidad Autónoma de Madrid, Spain.
Villarroya
M
M
Lara
B
B
Olmos
V
V
Gilabert
J A
JA
López
M G
MG
Martínez-Sierra
R
R
Borges
R
R
García
A G
AG
D000818:Animals; D001464:Barium / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D002838:Chromaffin System / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004246:Dimethylphenylpiperazinium Iodide / Q000378:metabolism; D005730:Ganglionic Blockers / Q000494:pharmacology; D006584:Hexamethonium Compounds / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000494:pharmacology*; D010276:Parasympatholytics / Q000494:pharmacology*; D011188:Potassium / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism
D015220:Calcium Channels; D002395:Catecholamines; D005730:Ganglionic Blockers; D006584:Hexamethonium Compounds; D018733:Nicotinic Antagonists; D010276:Parasympatholytics; D000644:Quaternary Ammonium Compounds; D015222:Sodium Channels; D001464:Barium; C013934:octylonium; D004246:Dimethylphenylpiperazinium Iodide; D011188:Potassium; D002118:Calcium