Differences between the mechanisms of adrenaline and noradrenaline secretion from isolated, bovine, adrenal chromaffin cells.

Cultured, bovine, adrenal medullary chromaffin cells have been used to study the secretion of adrenaline (A) and noradrenaline (NA) in response to two consecutive stimulation periods. Cells were first exposed to nicotine, then rapidly washed before being exposed to elevated K+ levels. Both A and NA cell types secreted their catecholamine in response to nicotine; however, NA cells secreted 3 times more of their catecholamine stores as did A cells. The NA cells were desensitized to stimulation by K+ if they had previously been exposed to nicotine. A cells, on the other hand, were up to twice as responsive to K+ stimulation after having been stimulated with nicotine, in spite of substantial depletion of their catecholamine stores. This sensitization of A cells to K+ was neither due to carryover of nicotine from the first stimulation period, nor to accumulation of calcium in the cells during the nicotinic stimulation. The results suggest that stimulus-secretion coupling or the exocytotic machinery in A and NA chromaffin cells is different. These differences may contribute to the ratio A:NA secreted from the adrenal medulla during stress.