Differential Ca2+ responses of adrenergic and noradrenergic chromaffin cells to various secretagogues

Abstract

The effects of several physiological agonists on the cytosolic Ca2+ concentration ([Ca2+]i) of immunnocytochemically identified single adrenergic and noradrenergic bovine chromaffin cells were compared. No differences were observed in the responses to stimulation by high-K+ solutions with or without BAY K 8644, suggesting that the density and properties of voltage-dependent Ca2+ channels were similar in both cell types. The increase of [Ca2+]i induced by acetylcholine was greater in adrenergic cells, and this was due to differences in the response mediated through nicotinic receptors. The responses to bradykinin and to ATP were slightly greater in noradrenergic cells. Only a small fraction of the cells (18-28%) was responsive to ATP. The responses to angiotensin II and to histamine were much greater in adrenergic than in noradrenergic cells. Histamine was almost a selective stimulator of adrenergic cells. These differences suggest differential distribution of functional membrane receptors in both cell types and may be relevant to understanding the differential contribution of epinephrine- and norepinephrine-secreting cells during stressful conflicts in physiological or pathophysiological situations.