Sodium-dependent and sodium-independent nicotine-evoked catecholamine release from cat adrenals

Cat adrenal glands were stimulated with nicotine under Na-free conditions; subsequently, Na was gradually introduced as a continuously increasing gradient from 0 to 134 mM. With this experimental approach two catecholamine secretory peak responses were obtained: one was Na-independent and the second was dependent of this cation. This second response was greater in magnitude than the first and selectively blocked by (+)PN200-110, a potent dihydropiridine Ca channel blocker. The results suggest that Na, although not essential to evoke some degree of secretion, plays, however, a prominent role in amplifying the nicotine-secretory response by causing cell depolarization and opening of voltage-dependent Ca channels.