Direct observation of membrane retrieval in chromaffin cells by capacitance measurements

This study was focussed on the identification of the endocytic organelles i n chromaffin cells which retrieve large, dense core vesicle (LDCV)-membrane components from the plasma membrane. For this purpose, 'on-cell' capacitan ce measurements and electron microscopy were employed. We found capacitance steps and capacitance flickers, corresponding to single exo- and endocytic events. The analysis revealed that the total membrane surface of completel y fused LDCVs is recycled by large endocytic vesicles and smaller, most lik ely clathrin-coated vesicles, at approximately the same ratio. These result s were confirmed by rapid-freeze immuno-electron microscopy, where an extra cellular marker was rapidly internalized into endocytic vesicles that morph ologically resembled LDCVs. (C) 2001 Federation of European Biochemical Soc ieties. Published by Elsevier Science B.V. All rights reserved.