DIFFERENTIAL CA2+ RESPONSES OF ADRENERGIC AND NORADRENERGIC CHROMAFFIN CELLS TO VARIOUS SECRETAGOGUES

The effects of several physiological agonists on the cytosolic Ca2+ co ncentration ([Ca2+](i)) of immunocytochemically identified single adre nergic and noradrenergic bovine chromaffin cells were compared. No dif ferences were observed in the responses to stimulation by high-K+ solu tions with or without BAY K 8644, suggesting that the density acid pro perties of voltage-dependent Ca2+ channels were similar in both cell t ypes. The increase of [Ca2+](i) induced by acetylcholine was greater i n adrenergic cells, and this was due to differences in the response me diated through nicotinic receptors. The responses to bradykinin and to ATP were slightly greater in noradrenergic cells. only a small fracti on of the cells (18-28%) was responsive to ATP. The responses to angio tensin II and to histamine were much greater in adrenergic than in nor adrenergic cells. Histamine was almost a selective stimulator of adren ergic cells. These differences suggest differential distribution of fu nctional membrane receptors in both cell types and may be relevant to understanding the differential contribution of epinephrine- and norepi nephrine-secreting cells during stressful conflicts in physiological o r pathophysiological situations.