Calcium Uptake and Catecholamine Secretion by Cultured Bovine Adrenal Medulla Cells

Abstract

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 blocks uptake induced by K⁺, nicotine, and veratridine, but not ⁴⁵Ca²⁺ uptake or secretion induced by Ionomycin. The EC₅₀ for nicotine is 3 μm for catecholamine secretion and 10 μm for ⁴⁵Ca²⁺ uptake, while the EC₅₀S for veratridinestimulated uptake and secretion are approximately the same (75 μm). 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 uptake of ⁴⁵Ca²⁺ and secretion of catecholamines stimulated by veratridine and 50 mm-K⁺ show saturation kinetics with respect to external calcium concentrations at about 2 mm. On the other hand, the uptake of ⁴⁵ Ca²⁺ 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.