SNARE-dependent membrane fusion initiates α-granule matrix decondensation in mouse platelets

Platelet α-granule cargo release is fundamental to both hemostasis and thrombosis. Granule matrix hydration is a key regulated step in this process, yet its mechanism is poorly understood. In endothelial cells, there is evidence for 2 modes of cargo release: a jack-in-the-box mechanism of hydration-dependent protein phase transitions and an actin-driven granule constriction/extrusion mechanism. The third alternative considered is a prefusion, channel-mediated granule swelling, analogous to the membrane “ballooning” seen in procoagulant platelets. Using thrombin-stimulated platelets from a set of secretion-deficient, soluble N-ethylmaleimide factor attachment protein receptor (SNARE) mutant mice and various ultrastructural approaches, we tested predictions of these mechanisms to distinguish which best explains the α-granule release process. We found that the granule decondensation/hydration required for cargo expulsion was (1) blocked in fusion-protein-deficient platelets; (2) characterized by a fusion-dependent transition in granule size in contrast to a preswollen intermediate; (3) determined spatially with α-granules located close to the plasma membrane (PM) decondensing more readily; (4) propagated from the site of granule fusion; and (5) traced, in 3-dimensional space, to individual granule fusion events at the PM or less commonly at the canalicular system. In sum, the properties of α-granule decondensation/matrix hydration strongly indicate that α-granule cargo expulsion is likely by a jack-in-the-box mechanism rather than by gradual channel-regulated water influx or by a granule-constriction mechanism. These experiments, in providing a structural and mechanistic basis for cargo expulsion, should be informative in understanding the α-granule release reaction in the context of hemostasis and thrombosis.

OPTIMASI FORMULA MATRIKS KITOSAN DENGAN METILSELULOSA PADA PELEPASAN TERKENDALI SEDIAAN GRANUL TEOFILIN

The in vitro study was carried out on the release of active ingradient theophylline from granules prepared by moist granulation method. The granule matrix was prepared from the mixture of chitosan isolated from SwaIIo shrimp (Metapenaeus monoceros) (in accordance with the Protan Laboratories, Inc standard requirement) and methylceliuiose 1500 cps. The granules were filled into 850 mg capsules containing 200 mg theophylline. The maximum weight of chitosan and methylcellulose for each capsule was determined by factorial design 22.The result showed that, when the amount of chitosan was kept constant, an increase in the amount of methylcellulose will increase the release rate of theophylline from granules. The optimum weight of chitosan and methyIceIIuIose are 609.24 mg and 20.00 mg, respectively for one capsule.

Granule matrix property and rapid “kiss-and-run” exocytosis contribute to the different kinetics of catecholamine release from carotid glomus and adrenal chromaffin cells at matched quantal size

Catecholamine-containing small dense core granules (SDCGs, vesicular diameter of ∼100 nm) are prominent in carotid glomus (chemosensory) cells and some neurons, but the release kinetics from individual SDCGs has not been studied in detail. In this study, we compared the amperometric signals from glomus cells with those from adrenal chromaffin cells, which also secrete catecholamine but via large dense core granules (LDCGs, vesicular diameter of ∼200–250 nm). When exocytosis was triggered by whole-cell dialysis (which raised the concentration of intracellular Ca2+ ([Ca2+]i) to ∼0.5 µmol/L), the proportion of the type of signal that represents a flickering fusion pore was 9-fold higher for glomus cells. Yet, at the same range of quantal size (Q, the total amount of catecholamine that can be released from a granule), the kinetics of every phase of the amperometric spike signals from glomus cells was faster. Our data indicate that the last phenomenon involved at least 2 mechanisms: (i) the granule matrix of glomus cells can supply a higher concentration of free catecholamine during exocytosis; (ii) a modest elevation of [Ca2+]i triggers a form of rapid “kiss-and-run” exocytosis, which is very prevalent among glomus SDCGs and leads to incomplete release of their catecholamine content (and underestimation of their Q value).

ESSENTIAL FACTORS INFLUENCING TUNNELING GIANT MAGNETORESISTANCE OF GRANULAR FILMS

A series of ferromagnetic-insulator granular films were prepared at room temperature with a spc350 multi-target magnetron controlled sputtering system and all of the tunneling giant magnetoresistences were measured with the conventional four probes method. Experimental results revealed that TMR depends strongly on the magnetic granule, matrix and the size distribution of magnetic granules. Accordingly, a modified phenomenological theory is presented to investigate comprehensively the effect of the magnetic granule, matrix and the size distribution of magnetic granules on the TMR. In this theory, the size distribution of granules was described by the log-normal function and all granules can be divided into three categories which have different contributions on TMR by two critical sizes: D1(T) as the critical size distinguishing superparamagnetic granules from single domain ferromagnetic granules and D2(T) as the critical size distinguishing the single domain from the multi-domain. The calculated results, including TMR versus applied magnetic field, measured temperature, granule size or volume fraction, are in agreement with the experiments when the single domain ferromagnetic granules play a key role in TMR for granular films, which indicates that our modified model is reasonable.