Fig. 6.

Schematic model illustrating constitutive vs. regulated secretory pathways (A), with B and C indicating magnifications of secretory granules to illustrate the catecholamine biosynthetic pathway (B) and the catecholamine-regulated secretory pathway (C). For most definitions of abbreviations, see Table 2. TYR, tyrosine; DOPA, dihydroxyphenylalanine; DA, dopamine; NE, norepinephrine; EPI, epinephrine; AADC, aromatic amino acid decarboxylase; NET, norepinephrine transporter; VAMP, vesicle-associated membrane protein; SCAMP, secretory carrier membrane protein; PNMT, phenylethanolamine N-methyltransferase; DBH, dopamine β-hydroxylase.