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121.
Aim A fraction of vesicles in cells treated with hypertonic solution exhibit multiple dense cores and this is enhanced by treatment
with l-3,4–dihydroxyphenylalanine (l-DOPA). These cells were examined to determine if the multicore vesicles are the product of endocytosis or homotypic fusion.
Methods Electron microscopy was used to determine the number of multicore vesicles and amperometry was used to examine if the multicore
vesicles are a competent fraction of the readily releasable pool.
Results In this study, we observed that a substantial portion (15.3%) of large dense core vesicles in PC12 cells contained multiple
cores in hypertonic saline loaded with l-DOPA, and amperometric measurements show a bimodal distribution of quantal sizes in treated cells.
Conclusions The results suggest that the multicored vesicles are formed from homotypic fusion of LCDVs prior to exocytosis. 相似文献
122.
Background
Speciation often occurs in complex or uncertain temporal and spatial contexts. Processes such as reinforcement, allopatric divergence, and assortative mating can proceed at different rates and with different strengths as populations diverge. The Central American Midas cichlid fish species complex is an important case study for understanding the processes of speciation. Previous analyses have demonstrated that allopatric processes led to species formation among the lakes of Nicaragua as well as sympatric speciation that is occurring within at least one crater lake. However, since speciation is an ongoing process and sampling genetic diversity of such lineages can be biased by collection scheme or random factors, it is important to evaluate the robustness of conclusions drawn on individual time samples. 相似文献123.
124.
The oxygen isotope composition (δ18O) of atmospheric CO2 is among a very limited number of tools available to constrain estimates of the biospheric gross CO2 fluxes, photosynthesis and respiration at large scales. However, the accuracy of the partitioning strongly depends on the extent of isotopic disequilibrium between the signals carried by these two gross fluxes. Chamber‐based field measurements of total CO2 and CO18O fluxes from foliage and soil can help evaluate and refine our models of isotopic fractionation by plants and soils and validate the extent and pattern of isotopic disequilibrium within terrestrial ecosystems. Owing to sampling limitations in the past, such measurements have been very rare and covered only a few days. In this study, we coupled automated branch and soil chambers with tuneable diode laser absorption spectroscopy techniques to continuously capture the δ18O signals of foliage and soil CO2 exchange in a Pinus pinaster Aït forest in France. Over the growing season, we observed a seasonally persistent isotopic disequilibrium between the δ18O signatures of net CO2 fluxes from leaves and soils, except during rain events when the isotopic imbalance became temporarily weaker. Variations in the δ18O of CO2 exchanged between leaves, soil and the atmosphere were well explained by theory describing changes in the oxygen isotope composition of ecosystem water pools in response to changes in leaf transpiration and soil evaporation. 相似文献
125.
Adams KL Maxson MM Mellander L Westerink RH Ewing AG 《Cellular and molecular neurobiology》2010,30(8):1235-1242
Fast neuromodulatory effects of 17-β-estradiol (E2) on cytosolic calcium concentration ([Ca2+]
i
) have been reported in many cell types, but little is known about its direct effects on vesicular neurotransmitter secretion
(exocytosis). We examined the effects of E2 on depolarization-evoked [Ca2+]
i
in PC12 cells using fluorescence measurements. Imaging of [Ca2+]
i
with FURA-2 revealed that depolarization-evoked calcium entry is inhibited after exposure to 10 nM and 10 μM E2. Calcium
entry after exposure to 50 μM E2 decreases slightly, but insignificantly. To relate E2-induced changes in [Ca2+]
i
to functional effects, we measured exocytosis using amperometry. It was observed that E2 in some cells elicits exocytosis
upon exposure. In addition, E2 inhibits depolarization-evoked exocytosis with a complex concentration dependence, with inhibition
at both physiological and pharmacological concentrations. This rapid inhibition amounts to 45% at a near physiological level
(10 nM E2), and 50% at a possible pharmacological concentration of 50 μM. A small percentage (22%) of cells show exocytosis
during E2 exposure (“Estrogen stimulated”), thus vesicle depletion could possibly account (at least partly) for the E2-induced
inhibition of depolarization-evoked exocytosis. In cells that do not exhibit E2-stimulated release (“Estrogen quiet”), the
E2-induced inhibition of exocytosis is abolished by a treatment that eliminates the contribution of N-type voltage-gated calcium
channels (VGCCs) to exocytosis. Overall, the data suggest that E2 can act on N-type VGCCs to affect secretion of neurotransmitters.
This provides an additional mechanism for the modulation of neuronal communication and plasticity by steroids. 相似文献
126.
NADIA BRUYNDONCKX FRANÇOIS BIOLLAZ SYLVAIN DUBEY JÉRÔME GOUDET PHILIPPE CHRISTE 《Molecular ecology》2010,19(13):2770-2778
Movements and spatial distribution of host populations are expected to shape the genetic structure of their parasite populations. Comparing the genetic patterns of both interacting species may improve our understanding of their evolutionary history. Moreover, genetic analyses of parasites with horizontal transmission may serve as indicators of historical events or current demographic processes that are not apparent in the genetic signature of their hosts. Here, we compared mitochondrial variation in populations of the ectoparasitic mite Spinturnix myoti with the genetic pattern of its host, the Maghrebian bat Myotis punicus in North Africa and in the islands of Corsica and Sardinia. Mite mitochondrial differentiation among populations was correlated with both host mitochondrial and nuclear differentiation, suggesting spatial co‐differentiation of the lineages of the two interacting species. Therefore our results suggest that parasite dispersal is exclusively mediated by host movements, with open water between landmasses as a main barrier for host and parasite dispersal. Surprisingly the unique presence of a continental European mite lineage in Corsica was inconsistent with host phylogeographical history and strongly suggests the former presence of European mouse‐eared bats on this island. Parasites may thus act as biological tags to reveal the presence of their now locally extinct host. 相似文献
127.
We report a significantly improved system for studying single-copy lacZ operon fusions in Yersinia enterocolitica: a simple procedure for the stable integration of lacZ operon fusions into the ara locus and a strain with a deletion mutation that abolishes the low level of endogenous β-galactosidase activity. 相似文献
128.
Serum testosterone (T) was studied developmentally in DBA/1/Bg and C57BL/10/Bg inbred mice, as well as in their reciprocal F1 hybrids. Testosterone determinations were made using a radioimmunoassay. At 35 and 40 days , DBA/1/Bg mice had higher levels of T than C57BL/10/Bg males. Comparison of the regression coefficients for the serum T values over days 30, 35, 40, and 50 also indicated statistical differences in the two curves of developmental changes in T. The pubertal rise in B10D1F1 but not D1B10F1 males was found to be steeper in slope over days 30, 35, 40, and 50 than that of C57BL/10/Bg males. These data suggest that during the pubertal period there may be a more rapid increase in serum T titer associated with the DBA/1 Y-chromosome. However, the developmental curves of T for the two reciprocal hybrids were not statistically different from each other or from that of the DBA/1/Bg males. These findings are suggestive of a Y-chromosome effect on developmental changes in T and of a genetic correlation with intermale aggression. 相似文献
129.
JÉRÔME MUNZINGER 《Botanical journal of the Linnean Society. Linnean Society of London》2001,137(1):91-97
While working on a treatment of Violaceae for the Flore de Nouvelle-Caledonie et dependences , two new species were recognized, Agatea veillonii Munzinger and A. lecointei Munzinger. These species are here described and illustrated. Some taxonomic notes and a regional identification key are provided. 相似文献
130.