Spatial buffering

Although spatial buffering can effectively prevent accumulation of moderate concentrations of extracellular K+, this diffusion process may be inadequate at very high rates... 

FIGURE 5-14 Spatial buffering by astrocytes. This conceptual diagram indicates the pathways available for potassium ions to diffuse through the glial syncytium (light red) subsequent to their release from neuronal membranes (dark red) during neural activity. 

Pow, D. V., and Barnett, N. L. (1999). Changing patterns of spatial buffering of glutamate in developing rat retinae are mediated by the Muller cell glutamate transporter GLAST. Cell Tissue Res. 297, 57-66. 

Two types of sulfoximinocarboxylates (analogous to sulfinylcarboxylates 16), namely 5 -aryl-5 -methoxycarbonylmethyl-A(-methyl sulfoximine 36 and -methyl-5 -phenyl-A(-ethoxycarbonyl sulfoximine 37, were subjected to hydrolysis in the presence of PLE in a phosphate buffer. As a result of a kinetic resolution, both the enantiomerically enriched recovered substrates and the products of hydrolysis and subsequent decarboxylation 38 and 39, respectively, were obtained with moderate to good ees (Equations 20 and 21). Interestingly, in each case the enantiomers of the substrates, having opposite spatial arrangement of the analogous substituents, were preferentially hydrolysed. This was explained in terms of the Jones PLE active site model. ... 

When a sample is loaded into the capillary, a transient diastereomer complex may be formed between the sample and the selector. The differing mobilities of the diastereomers in the buffer solution in the presence of an electric field is the reason for the separation. The differences of mobility between the diastereomers are the result of different effective charge sensitivities caused by the different spatial orientations of diastereomers or the specific intermolecular interactions between them. 

Biofilms enhance bacteria-DOM interactions by several means. Their spatial and chemical heterogeneity provides additional sorption sites for DOM compared with clean surfaces. Their loose architecture with interstitial voids and channels increases diffusivity and to some extent allows convective flow within biofilm structures. Because bacteria metabolize organic matter sorbed to the biofilm, a diffusion flux from the free water to the biofilm is maintained. Large proportions of organic matter sorbed to the biofilm are not instantly turned over but remain in the biofilm as a reservoir, which buffers direct effects of DOM depletion in the water column. 

The Ca2+-concentration in a nerve terminal depends on the number and temporal pattern of action potentials, the effectiveness of these action potentials to open Ca2+-channels, and the properties and concentrations of Ca2+-buffers. Not only the time course of changes in Ca2+-concentrations, but also the spatial distribution of Ca2+, is important because Ca2+ is not uniformly distributed in a nerve terminal. Moreover, the Ca2+-dynamics of a nerve terminal differ between nerve terminals, and play a central role in synaptic plasticity (e.g., see Rozov et al., 2001 Zucker and Regehr, 2002). 

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