Glutamine transport in cerebellar granule cells in culture.

In the present study, uptake of glutamine by rat cerebellar granule cells, a predominantly glutamatergic nerve cell population, has been investigated. Glutamine is taken up by granule cells via at least three transport systems, A, ASC and L. The L-type low affinity system (K(m) = 2.6 mM) is the major transport system in the absence of Na+. The systems A and ASC represent the Na(+)-dependent transport routes, both with almost identical high affinity for glutamine (K(m) = 0.26 mM). Similar transport systems for glutamine are also found in cerebral cortical neurons, a predominantly GABAergic nerve cell population, and cerebral cortical astrocytes. The glutamine transport properties in granule cells, however, show a series of differences from that of cortical neurons and astrocytes: (1) uptake of glutamine by granule cells is primarily mediated by system A (54%), while contributions by system A in cortical neurons and astrocytes are less than 30%; (2) granule cells exhibit strikingly higher transport efficiency for glutamine (V(max)/K(m) = 20 min(-1) for system A as compared to the V(max)/K(m) ratio of 5 min(-1) in cortical neurons and astrocytes), and (3) the initial uptake rates and the steady-state accumulation levels of glutamine are two- to threefold higher in granule cells than that of cortical neurons and astrocytes. These results taken together suggest that in accordance with the important need to replenish the neurotransmitter pool of glutamate, glutamatergic neurons exhibit highly efficient transport systems to accumulate glutamine, one of the major precursors of glutamate.

Synthesis and pharmacological evaluation of phenylacetamides as sodium-channel blockers.

The synthesis and structure-activity relationships of a series of phenylacetamides related to N-[3-(2,6-dimethyl-1-piperidinyl)propyl]-alpha-phenylbenzeneacetamide (1) (PD85639) acting at the voltage-dependent Na+ channel are described. All structural variations for this study were made in the phenylacetic acid portion of these molecules, and the compounds were synthesized by coupling the appropriately substituted phenylacetic acid derivative with 3-[1-(2,6-dimethyl)piperidinyl]-propanamine using standard methods of amide formation. Compounds were tested as inhibitors of [3H]batrachtoxinin binding in rat neocortical membranes and also as inhibitors of veratridine-induced Na+ influx in Chinese hamster ovary cells expressing type IIA Na+ channels. Diphenylacetic acid derivatives with halogenated aromatic rings (12-15) were very potent in both assays, while alkoxy and alkyl substitution did not affect activity (16 and 17). Selected compounds were tested as potential neuroprotective agents in two cell culture assays involving inhibition of veratridine-induced and hypoxia-induced lactate dehydrogenase release. Compound 15 was equipotent with flunarizine, a reference compound in both neuroprotection assays.

Spatial analysis and mapping the annual mean concentrations of acidity and major ions in precipitation over the United Kingdom in 1986.

The composition of precipitation is being monitored in collectors sited throughout the United Kingdom. In the first year, 1986, hydrogen ion, nitrate, ammonium and non-marine sulphate were measured in samples from 47 sites and annual mean concentrations determined. Spatial analysis based on Regionalized Variable Theory revealed autocorrelation in all four ions and reasonable bounded models were fitted to the sample variogram of all four. These were then used to estimate values of a fine mesh grid by simple kriging, and the estimates were then contoured. The estimation errors were similarly mapped, and both sets of maps are presented. The maps show that concentrations of these ions are greatest in eastern parts of the country, as expected from consideration of European emissions and weather patterns. For the first time estimation errors were also mapped and show how the network could be improved.

Measurements of nitrogen dioxide concentrations at rural sites in the United Kingdom using diffusion tubes.

Nitrogen dioxide concentrations have been measured at rural sites in the United Kingdom and have revealed a marked spatial variation. The annual mean NO2 concentration varies from approximately 1 microg Nm-3 in Northern Ireland to approximately 7 microg Nm-3 in East Anglia. Though the temporal resolution of the diffusion tube method is limited by exposure periods of 2-4 weeks, it was possible to detect a marked seasonal variation in NO2 concentration at all sites, with higher values in the winter than in the summer. This is in contrast to the small seasonal variation previously observed at sites in London. Sulphur dioxide concentrations were measured daily using a bubbler method and, if expressed in terms of mass of sulphur and nitrogen, the SO2 and NO2 annual mean concentrations were similar. This is in contrast to an S/N ratio of greater than 3 in total UK emissions of SO2 and NOx. It seems likely that this difference is due to a combination of the different spatial distributions and heights of emissions of SO2 and NOx, the influence of local sources of NOx, and the smaller S/N ratio in Continental European emissions.