Peripheral vesicles

Fig. 2 Routine preparation of a hydrogenosome (H) in Trichomonas vaginalis (a), Tri-trichomonas foetus (b), and Monocercomonas sp. (c). Note that in T. foetus the hydrogenosome is spherical, enveloped by a double membrane (arrows), and presents a single peripheral vesicle, whereas in T vaginalis several peripheral vesicles are seen surrounding the organelle (arrows) and in Monocercomonas the hydrogenosome is very elongated. ER, endoplasmic reticulum N, nucleus. Bars = 100 nm. (From Benchimol 2001 Diniz and Benchimol 1998)...

Fig. 5 Thin sections of a I foetus (a) and a fungal (b) hydrogenosome (H) from Neo-callimastix frontalis. Both hydrogenosomes are clearly enveloped by a double membrane (arrow in (a), arrowheads in (b)). Invaginations of the hydrogenosome membrane were occasionally observed (arrow in (a)). The black spot in (a) is a calcium deposit in the peripheral vesicle (asterisks). CW, cell wall. Bars = 100 nm. (Fig. 5a from Benchimol, unpublished Fig. 5b, from Benchimol et al. 1997)...

Fig. 6 Carbohydrates in hydrogenosomes. Monocercomonas sp. after the Thiery technique (a). The hydrogenosomal membranes are positive for carbohydrates, b T. foetus cryosection labeled with gold-conjugated WGA. Hydrogenosome (H) shows that the membrane lining the peripheral vesicle, but not other portions of the organelle, is labeled. Bars = 100 nm. (Fig. 6a from Diniz and Benchimol 1998 Fig. 6b from Benchimol et al. 1996a)...

Fig. 7 Freeze-fracture images of hydrogenosomes from T. foetus, a Fractured cell showing a prominent Golgi (G) with several lamellae and fenestrae, as well profiles of endoplasmic reticulum (ER) in close proximity (arrows) with hydrogenosomes (H). Bar = 100 nm. b Hydrogenosomes from an isolated fraction observed by freeze-fracture. Note the clusters of intramembranous particles forming rosettes (arrow). The peripheral vesicle is smooth and does not present clusters of particles or rosettes. Bar = 50 nm. (From Benchimol et al. 2001). c Two freeze-fractured hydrogenosomes exhibiting different fracture planes (arrows). Bar = 100 nm. (From Benchimol et al. 1996a)...

Fig. 8 Different views of T. foetus hydrogenosomes ( ) after field-emission scanning electron microscopy (FESEM) (a) and freeze-etching (b,c). An isolated hydrogenosome obtained from T. foetus observed by FESEM, where details of its surface can be seen, b A calcium deposit in the peripheral vesicle (asterisk) c shows that the peripheral vesicle (arrow) presents a smooth surface, distinct from the organelle body. Bars = 50 nm. (From Benchimol 2000)...

Golgi apparatus A system of flattened membrane-bounded vesicles often stacked into a complex. Numerous small vesicles are found peripheral to the Golgi and contain secretory material packaged by the Golgi. Involved in the packaging and processing of macromolecules for secretion and for delivery to other cellular compartments. 

It is a very large vesicle enclosed by a single membrane called the tonoplast. Vacuoles tend to be smaller in young cells, but in mature cells, they may occupy more than 50% of the cell s volume. Vacuoles occupy the center of the cell, with the cytoplasm being located peripherally around it. They resemble the lysosomes of animal cells. 

ACh and considered to be the vesicles in the labile releasable pool. The evidence for and the actual mechanism of the vesicular release of ACh, mostly gained from studies at peripheral synapses, has been covered in Chapter 4. 

ATP certainly fulfils the criteria for a NT. It is mostly synthesised by mitochondrial oxidative phosphorylation using glucose taken up by the nerve terminal. Much of that ATP is, of course, required to help maintain Na+/K+ ATPase activity and the resting membrane potential as well as a Ca +ATPase, protein kinases and the vesicular binding and release of various NTs. But that leaves some for release as a NT. This has been shown in many peripheral tissues and organs with sympathetic and parasympathetic innervation as well as in brain slices, synaptosomes and from in vivo studies with microdialysis and the cortical cup. There is also evidence that in sympathetically innervated tissue some extracellular ATP originates from the activated postsynaptic cell. While most of the released ATP comes from vesicles containing other NTs, some... 

In contrast, iproniazid, introduced in 1951 for treatment of tuberculosis, induced euphoria and was described as a psychic energiser . In fact, these patients, when given iproniazid, could become quite disruptive and this action was regarded as an undesirable side-effect However, its beneficial effects in depression were soon recognised and it was regarded as the first effective antidepressant drug. Studies of peripheral sympathetic neurons, later extended to noradrenergic neurons in the brain, showed that iproniazid irreversibly inhibits the catalytic enzyme, monoamine oxidase (MAO). Because only cytoplasmic monoamines are accessible to MAO, inhibition of this enzyme first increases the concentration of the pool of soluble transmitter but this leads to a secondary increase in the stores of vesicle-bound transmitter i.e. the pool available for impulse-evoked release (Fillenz and Stanford 1981). 

Peripheral Cuanethidine Uptake by transmitter vesicles in nerve depletes and replaces norepinephrine in neurosecretory vesicles. 

Cysteine string protein (CSP) Cytochrome b561 Peripheral membrane protein that is paimitoylated on >10 cysteines. May have a role in Ca2+ sensitivity of exocytosis. Electron-transport protein required for intravesicular monooxygenases in subsets of secretory vesicles. Required for dopamine- -hydroxylase and peptide amidase activity. 

Reserpine blocks vesicular storage of monoamines, prolonging their presence in cytoplasm. There they are degraded by MAO, leading to a depletion of monoamines in synaptic terminals of central and peripheral neurons, so that little or no neurotransmitter is released when the neuron depolarizes (Oates 1996). Reversal of this process requires synthesis of new vesicles, which occurs over a period of days to weeks after discontinuation of the drug. 

The main limitation to the clinical use of the MAOIs is due to their interaction with amine-containing foods such as cheeses, red wine, beers (including non-alcoholic beers), fermented and processed meat products, yeast products, soya and some vegetables. Some proprietary medicines such as cold cures contain phenylpropanolamine, ephedrine, etc. and will also interact with MAOIs. Such an interaction (termed the "cheese effect"), is attributed to the dramatic rise in blood pressure due to the sudden release of noradrenaline from peripheral sympathetic terminals, an event due to the displacement of noradrenaline from its mtraneuronal vesicles by the primary amine (usually tyramine). Under normal circumstances, any dietary amines would be metabolized by MAO in the wall of the gastrointestinal tract, in the liver, platelets, etc. The occurrence of hypertensive crises, and occasionally strokes, therefore limited the use of the MAOIs, despite their proven clinical efficacy, to the treatment of atypical depression and occasionally panic disorder. 

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