The cellular response of individual adrenal medullary cells to a prolonged stimulation with carbamylcholine (carbachol) was studied using microcolumn high-performance liquid chromatography (MHPLC) with electrochemical detection. Chromaffin cells will not release all of their catecholamine stores when continuously exposed to a secretagogue. The process of desensitization prevents the continued release of catecholamines after a certain percentage of chemical stores have been depleted. The percentage of a cell's chemical stores released upon stimulation was determined, and whether there is a difference in release between the cell types was examined. A single cell was exposed to a stimulation solution for 5.0 min at 25 degrees C. Approximately 80% of the solution was removed and analyzed on a microcolumn reversed-phase chromatography column. A lysing solution was immediately added to the miniaturized vial which still contained the cell, and this solution was also analyzed chromatographically. The first run was used to determine the amount of catecholamine the cell released upon stimulation. The second run determined the amount of catecholamine that remained in the cell. From these values the percentage of catecholamine released was calculated. Twenty-seven individual cells were studied by this method, and 22 could be classified as norepinephrine or epinephrine dominant. There was no statistical difference in the amount of catecholamine the norepinephrine dominant cells released (14 +/- 5%, n = 11) as compared to the epinephrine dominant cells (12 +/- 4%, n = 11).