Blocking effects of otilonium on Ca2+ channels and secretion in rat chromaffin cells.
We describe here the effects of otilonium bromide (an anticholinergic agent widely used as an intestinal spasmolytic) on whole-cell currents through Ca2+ channels (IBa) and catecholamine secretion in rat adrenal glands and isolated rat chromaffin cells. Otilonium blocked the peak IBa current in voltage-clamped chromaffin cells in a concentration-dependent manner; the IC50 to block IBa was 4.7 microM. Blockade was not accompanied by a significant shift in the I-V relationship for IBa, suggesting that such blockade was not affecting a specific subtype of Ca2+ channel. When given intracellularly through the patch pipette, otilonium (10 microM) did not block IBa. However, its external application to the same cell (10 microM) reversibly reduced IBa by 70%. Otilonium caused a concentration-dependent blockade of catecholamine release from perfused rat adrenal glands intermittently stimulated with methacholine, high K+ or histamine. The IC50 to block secretion after a 5 min incubation with otilonium was 0.02, 0.7 and 3 microM, respectively, for methacholine, K+ and histamine. The blocking effects of otilonium were fully reversible at concentrations below 10 microM. The Ca2+ channel agonist Bay K 8644 (methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyr idine-5- carboxylate) partially antagonized the effects of otilonium on K(+)-evoked secretion and accelerated the time course of recovery from inhibition. The results are compatible with the idea that otilonium blocks Ca2+ entry into chromaffin cells by blocking voltage-dependent Ca2+ channels. This would lead to a limitation in the rise in cytosolic Ca2+ at secretory sites and to inhibition of catecholamine release in response to stimulation of chromaffin cells.
Gandía
L
L
Departamento de Farmacología y Medicina Física, Universidad de la Laguna, Tenerife, Spain.
López
M G
MG
Villarroya
M
M
Gilabert
J A
JA
Cárdenas
A
A
García
A G
AG
Borges
R
R
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects*; D002838:Chromaffin System / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005260:Female; D008297:Male; D010276:Parasympatholytics / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D051381:Rats; D013997:Time Factors
D015220:Calcium Channels; D010276:Parasympatholytics; D000644:Quaternary Ammonium Compounds; C013934:octylonium