EVIDENCE AGAINST THE SWELLING HYPOTHESIS FOR INITIATION OF EXOCYTOSISIN TERMINALS OF CHROMAFFIN CELL PROCESSES

Exocytosis of transmitter-containing granules was directly visualized in neurite terminals of cultured chromaffin cells under a video-enhanc ed contrast microscope. The granule diameter did not change immediatel y before their exocytotic responses. Large granules responded as early as small ones. These findings are inconsistent with the swelling hypo thesis for initiation of exocytosis.