Exocytosis: the common release mechanism of secretory granules in glandular cells, neurosecretory cells, neurons and paraneurons

Abstract

Exocytotic granule release in glandular cells (exocrine and endocrine), neurosecretory cells, neurons and paraneurons was discussed. Attention was focused on the neurosecretory terminals in the mammalian posterior pituitary gland and adrenomedullary cells. The concept of "exocytosis-vesiculation sequence" proposed by Douglas and Nagasawa was introduced. This theory states that the exocytotic release of secretory granules was followed by the mechanism of granule membrane recovery; this process occurred at the bottom of the exocytotic pit in the form of coated microvesicles. Experimental results were presented which substantiated the theory for the transformation of coated microvesicles into smooth microvesicles. The origin and the nature of long enigmatic "synaptic vesicles" in the posterior pituitary gland was thus explained. The exocytotic release probably operates as the general and perhaps sole mechanism of granule release in a variety of glandular cells, neurosecretory cells, neurons and paraneurons.