Quantal Secretion of Catecholamines Measured from Individual Bovine Adrenal Medullary Cells Permeabilized with Digitonin.

Abstract
Secretion of catecholamines from individual bovine adrenal medullary cells grown in primary culture has been investigated. Oxidation of catecholamines with a carbon-fiber electrode adjacent to the cells results in changes in current, which give a real-time measure of catecholamine secretion. However, permeabilization of a cell by exposure to 20 uM digitonin for 15 s results in a Ca 2-+ -dependent secretion, and the contents of individual vesicles are detected in the form of sharp spikes. The rate at which spikes occur is a function of the Ca 2+ concentration in the external media, and reaches a maximum at 19 microM Ca 2+ . The area of the majority of spikes are less than 2 picocoulombs, corresponding to less than 6 x 106 Molecules detected per spike. Histograms of the spike areas are essentially independent of Ca 2+ concentration, indicating that the population of vesicles which undergo exocytosis is the same for all concentrations. Secretion from these cells has also been examined under conditions where exocytosis would not be expected to occur. Long exposure of individual cells to 20 micro M digitonin results in Ca 2+ -independent secretion in the form of temporally broadened spikes, consistent with rupture of the vesicles inside the cell. Hypoosmotic solutions result in transient secretion which is in the form of a broad envelope with few spikes.

This publication has 0 references indexed in Scilit: