DIRECT OBSERVATION OF EPINEPHRINE AND NOREPINEPHRINE COSECRETION FROM INDIVIDUAL ADRENAL-MEDULLARY CHROMAFFIN CELLS

Cyclic voltammetry at Nafion-coated carbon fiber microelectrodes has been used to monitor directly the release of catecholamines from individual adrenal medullary chromaffin cells and to identify the released catecholamine as epinephrine or norepinephrine. The cultured cells were induced to secrete by exposure to 100-mu-M nicotine, a recognized secretagogue at these cells. Each cell contains on average 167 fmol of catecholamines, and the secretion event involves only a small percentage of the total stores for a time interval of less than 60 s. Identification of epinephrine and norepinephrine is accomplished because of differences in the rates of intracyclization for the oxidized forms of these compounds which results in differences in the shapes of their voltammograms. Approximately 75% of the cells studied released only epinephrine or norepinephrine in response to a 100-mu-M nicotine stimulus, while 25% released mixtures of both catecholamines. The ratio of epinephrine:norepinephrine releasing cells is in good agreement with the epinephrine:norepinephrine ratios of total catecholamine stores for the cell populations. Analysis of individual cell catecholamine content by microcolumn liquid chromatography following secretion measurements indicates that the individual cells release catecholamines in the same proportions in which they store catecholamines.