Hormone Secretion by Exocytosis with Emphasis on Information from the Chromaffin Cell System

This chapter discusses hormone secretion by exocytosis with an emphasis on information from the chromaffin cell system. Exocytosis is the general mechanism by which many hormones, transmitters, enzymes, and other special proteins and peptides are secreted from cells. Exocytosis means that the chemical species to be secreted is stored in a secretory vesicle, which, upon the appropriate stimulus, fuses with the cell membrane and deposits the vesicle contents outside the cell. The “handmaiden” of this process is usually calcium. In many cases, the ultimate signal for exocytosis seems to be an increase in the intracellular free calcium ion concentration. For many reasons, the chromaffin cell is the very best vantage point from which to examine the hormone-secretion process. From a biochemical viewpoint, the chromaffin cell has no peer, subcellular fractionation is simple, and the cells are easily cultured. Chromaffin cells in the adrenal medulla are joined and electrically coupled into cords of cells surrounded in the intact gland by an abundant fenestrated capillary bed.