Exocytosis of bovine chromaffin granules in Ficoll captured by rapid freezing.

Exocytosis of cultured bovine adrenal chromaffin cells was examined in a balanced salt solution containing Ficoll using rapid freezing followed by freeze-substitution. In solution without Ficoll, exposure to Ba2+ produced many exocytotic lumina between the cells; in most cases, these lumina were large and empty. When chromaffin cells were exposed to Ba2+ in Ficoll, it was possible to observe a small pore between the plasmalemma and each granule. The granule retained the dense contents when the pore was approximately 20 nm in diameter, and became empty when the pore was widened in 14% Ficoll. The addition of Ficoll made it easy to catch the events occurring during exocytosis of individual bovine chromaffin granules.