Calcium uptake and catecholamine secretion by cultured bovine adrenal medulla cells.
The uptake of 45Ca2+ and secretion of catecholamines by primary cultures of adrenal medulla cells were studied. Nicotine, veratridine, potassium, and Ionomycin stimulate both the accumulation of 45Ca2+ and the secretion of catecholamines. Nicotinic antagonists block 45Ca2+ uptake induced by nicotine, tetrodotoxin blocks 45Ca2+ uptake induced by veratridine, and D600 or secretion induced by Ionomycin. The EC50 for nicotine is 3 microM for catecholamine secretion and 10 microM for 45Ca2+ uptake, while the EC50s for veratridine-stimulated uptake and secretion are approximately the same (75 microM). Kinetic studies show that the uptake of Ca2+ is rapid and appears to precede the secretion of catecholamines, and that the rate of uptake declines rapidly. The 50 mM-K+ show saturation kinetics with respect to external calcium concentrations at about 2 mM. On the other hand, the uptake of 45Ca2+ stimulated by nicotine does not become saturated at external calcium concentrations of 10 mM although the secretion of catecholamines reaches a maximum at external calcium concentrations of 2 mM. The data suggest that depolarizing agents such as veratridine and 50 mM-K+ stimulate 45Ca2+ entry through voltage-sensitive calcium channels, while nicotinic agonists stimulate calcium entry through the acetylcholine receptor ion channels as well as through voltage-sensitive calcium channels.
D000313:Adrenal Medulla / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D002837:Chromaffin Granules / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005711:Gallopamil / Q000494:pharmacology; D009538:Nicotine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D013997:Time Factors; D014403:Tubocurarine / Q000494:pharmacology; D014701:Veratridine / Q000494:pharmacology
D002395:Catecholamines; D005711:Gallopamil; D009538:Nicotine; D014701:Veratridine; D011188:Potassium; D002118:Calcium; D014403:Tubocurarine