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Hormones of the Adrenal Gland
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
Catecholamines are synthesized from L-tyrosine, which may be present in the diet or derived from the hydroxylation of L-phenylalanine in the liver. Tyrosine is hydroxylated in the cytoplasm by tyrosine hydroxylase to L-dopa (3,4-dihydroxyphenylalanine). Dopa decarboxylase coverts dopa to dopamine in the cytoplasm. The dopamine is taken up by chromaffin granules, where it is converted to norepinephrine by dopamine β-hydroxylase. Some 20% of the chromaffin cells of the adrenal medulla contain norepinephrine; in the other 80% of cells, norepinephrine diffuses into the cytoplasm, where it is N-methylated by phenylethanolamine-N-methyl transferase. S-adenosylmethionine is the methyl donor, and epinephrine is synthesized. The catecholamines are bound to ATP and chromogranin (a soluble protein) and stored as specific granules (chromaffin granules).
Sympathetic Neurotransmission
Published in Kenneth J. Broadley, Autonomic Pharmacology, 2017
Synaptophysin may be a further vesicle membrane-spanning, Ca2+ binding protein, with the Ca2+ binding domain on the cytoplasmic side. It could serve as a Ca2+-regulated pore or junction between the vesicle and plasma membrane. Thus, the initial step for exocytosis may be the formation of a pore through which the vesicle contents pass across the neuronal membrane (Trimble et al. 1991). Another group of cytoplasmic Ca2+ binding proteins are the annexins. These can promote the fusion of chromaffin granules of the adrenal medulla in the presence of low Ca2+ levels and fatty acids. One of these, calpactin, is a strong candidate for linking the increase in [Ca2+]i to exocytosis by promoting the fusion of the vesicle with the inner surface of the plasma membrane (Trimble et al. 1991). Finally, it is suggested that specific GTP-binding proteins are also involved in the fusion of the vesicle with the plasma membrane (De Camilli & Jahn 1990).
The Water Permeability of Intact Subcellular Organelles
Published in Gheorghe Benga, Water Transport in Biological Membranes, 1989
Chromaffin granules are the storage site of catecholamines in the adrenal medulla. These organelles are osmotically tight, spheroidal vesicles,36 with an average in situ diameter of 115 nm.37 Chromaffin granules store the catecholamine neurohormones, epinephrine and norepinephrine, at very high internal concentration (0.5 M and 0.1 M, respectively), and deliver these hormones to the blood as a trigger of the body’s response to stress. In addition to the catecholamine hormones, chromaffin granules contain large concentrations (∼0.15 M) of nucleotides, primarily in the form of ATP, and chromogranins, which are a mixture of soluble, largely random-coil polypeptides. Chromaffin granules are close structural and functional analogs of neurotransmitter storage organelles and have been studied widely as model systems in this regard.38,39
Strong stimulation triggers full fusion exocytosis and very slow endocytosis of the small dense core granules in carotid glomus cells
Published in Journal of Neurogenetics, 2018
Amy Tse, Andy K. Lee, Noriko Takahashi, Alex Gong, Haruo Kasai, Frederick W. Tse
We found that even at 100 s after the UV flash, glomus cells retrieved only ∼40% of the vesicular membrane. In contrast, our previous study in corticotropes has shown that Cm returned to baseline within 10 s after the UV flash (Lee & Tse, 2001). The very slow classical endocytosis in glomus cells was correlated to the low densities of dynamin I, II and clathrin. It is generally accepted that the classical endocytosis in secretory cells is clathrin-dependent (Wu et al., 2014). In bovine chromaffin cells, pharmacological inhibitions of dynamin-II or clathrin were found to reduce slow endocytosis, and rapid endocytosis could be inhibited by the disruption of dynamin-I (Artalejo, Elhamdani, & Palfrey, 2002; Elhamdani, Azizi, Solomaha, Palfrey, & Artalejo, 2006b; Tsai et al.,2009). Since the cytoplasmic densities of dynamin I, II and clathrin in glomus cells were less than half of those in chromaffin cells (Figure 5(B)), it is probably that fewer endocytic machinery contribute to the slower classical endocytosis in glomus cells. The slow rate of endocytosis in glomus cells is probably related to their normally low secretory output for the paracrine/autocrine regulation of the carotid body functions. Thus, it is not essential for the glomus SDCGs to be rapidly replenished with transmitters. In contrast, chromaffin cells release large amount of hormones into the circulation during the ‘fight or flight response’ and a rapid replenishment of chromaffin granules would be crucial.