Catecholamine secretion from adrenal chromaffin cells of the toad (Caudiverbera caudiverbera): effect of monensin.
1. Stimulus-secretion coupling studies were carried out on adrenal chromaffin tissue from the toad. Catecholamine (CA) secretion was generated in response to acetylcholine (ACh) or high K+. 2. The response to ACh was found to be dependent on the presence of external Ca2+. The secretion induced by ACh or high K+ was inhibited by the Ca-channel blockers CoCl2 and nifedipine. 3. The specific Na+/H+ ionophore, monensin, induced a strong secretory response only if Na+ was present in the Ringer. Monensin's effect did not depend on external Ca2+ and was unaffected by the channel blockers tetrodotoxin or CoCl2. 4. Secretion induced by monensin was exocytotic as was shown by measuring ATP release using a photoluminescence, luciferine/luciferase assay. 5. In conclusion, in the toad, as in higher species, stimulus-secretion coupling involves Ca2+ entry from the external medium, possibly through voltage-dependent channels. Monensin is a potent secretagogue and the mechanism by which the ensuing elevation of intracellular Na+ concentration might induce a secretory response remains to be determined.
Laboratorio de Fisiología Celular, Facultad de Ciencias, Universidad de Chile, Viña del Mar.
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Nassar-Gentina
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Luxoro
D000109:Acetylcholine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism; D000311:Adrenal Glands / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001001:Anura; D002118:Calcium / Q000494:pharmacology; D002395:Catecholamines / Q000378:metabolism*; D002838:Chromaffin System / Q000187:drug effects / Q000378:metabolism*; D003035:Cobalt / Q000494:pharmacology; D008985:Monensin / Q000494:pharmacology*; D009543:Nifedipine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology
D002395:Catecholamines; D003035:Cobalt; D013779:Tetrodotoxin; D000255:Adenosine Triphosphate; D008985:Monensin; D012964:Sodium; C018021:cobaltous chloride; D009543:Nifedipine; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium