Anion currents and predicted glutamate flux through a neuronal glutamate transporter

Kinetic properties of a native, neuronal glutamate transporter were studied by using rapid applications of glutamate to outside-out patches excised from Purkinje neurons. Pulses of glutamate activated anion currents associated with the transporter that were weakly antagonized by the transporter antagonist kainate. In addition, kainate blocked a resting anion conductance observed in the absence of glutamate. Transporter currents in response to glutamate concentration jumps under a variety of conditions were used to construct a cyclic kinetic model of the transporter. The model simulates both the anion conductance and the glutamate flux through the transporter, thereby permitting several predictions regarding the dynamics of glutamate transport at the synapse. For example, the concentration-dependent binding rate of glutamate to the transporter is high, similar to binding rates suggested for ligand-gated glutamate receptors. At saturating glutamate concentrations, transporters cycle at a steady-state rate of 13/sec. Transporters are predicted to have a high efficiency; once bound, a glutamate molecule is more likely to be transported than to unbind. Physiological concentrations of internal sodium and glutamate significantly slow net transport. Finally, a fixed proportion of anion and glutamate flux is expected over a wide range of circumstances, providing theoretical support for using net charge flux to estimate the amount and time course of glutamate transport.     

Ex vivo expansion of genetically marked rhesus peripheral blood progenitor cells results in diminished long-term repopulating ability

The possibility of primitive hematopoietic cell ex vivo expansion is of interest for both gene therapy and transplantation applications. The engraftment of autologous rhesus peripheral blood (PB) progenitors expanded 10 to 14 days were tracked in vivo using genetic marking. Stem cell factor (SCF)/granulocyte colony-stimulating factor (G-CSF)-mobilized and CD34-enriched PB cells were divided into two equal aliquots and transduced with one of two retroviral vectors carrying the neomycin-resistance gene (neo) for 4 days in the presence of interleukin-3 (IL-3), IL-6, and SCF in the first 5 animals, IL-3/IL-6/SCF/Flt-3 ligand (FLT) in 2 subsequent animals, or IL-3/IL-6/SCF/FLT plus an autologous stromal monolayer (STR) in the final 2. At the end of transduction period, one aliquot (nonexpanded) from each animal was frozen, whereas the other was expanded under the same conditions but without vector for a total of 14 days before freezing. After total body irradiation, both the nonexpanded and expanded transduced cells were reinfused. Despite 5- to 13-fold higher cell and colony-forming unit (CFU) doses from the expanded fraction of marked cells, there was greater short- and long-term marking from the nonexpanded cells in all animals. In animals receiving cells transduced and expanded in the presence of IL-3/IL-6/SCF/FLT, engraftment by the marked expanded cells was further diminished. This discrepancy was even more pronounced in the animals who received cells transduced and expanded in the presence of FLT and autologous stroma, with no marking detectable from the expanded cells. Despite lack of evidence for expansion of engrafting cells, we found that the addition of FLT and especially STR during the initial brief transduction period increased engraftment with marked cells into a clinically relevant range. Levels of marked progeny cells originating from the nonexpanded aliqouts were significantly higher than that seen in previous 4 animals receiving cells transduced in the presence of IL-3/IL-6/SCF, with levels of 10% to 20% confirmed by Southern blotting from the nonexpanded IL-3/IL-6/SCF/FLT/STR graft compared with 0.01% in the original IL-3/IL-6/SCF cohort. These results suggest that, although expansion of PB progenitors is feasible ex vivo, their contribution towards both short- and long-term engraftment is markedly impaired. However, a brief transduction in the presence of specific cytokines and stromal support allows engraftment with an encouraging number of retrovirally modified cells.     

The Fanconi anemia complementation group C gene (FAC) suppresses transformation of mutant fibroblasts by the SV40 virus

Fanconi anemia (FA) is a heterogeneous genetic syndrome manifested by bone marrow failure and consisting of at least five complementation groups (A, B, C, D, E). Mutations in a gene termed FAC are responsible for the C complementation group, but the function of the FAC protein remains obscure. FA patients are also highly cancer-prone; the molecular basis for this susceptibility is unclear but has led to the hypothesis that the wild-type FA gene may act as a tumor suppressor. In vitro, mutant FA primary fibroblasts are 3- to 50-fold more sensitive than normal fibroblasts to transformation in culture by the SV40 virus. We confirmed this marked susceptibility to transformation of a FAC-mutant primary fibroblast cell line, GM449. We then introduced a copy of the wild-type FAC cDNA into GM449 cells using a recombinant adeno-associated virus (rAAV) vector. We found that GM449 cells transduced with a copy of the normal FAC cDNA by a FAC-rAAV vector were at least 10-fold less prone to form transformed foci. Diminished transformation potential of transduced cells was a specific effect of the FAC cDNA since GM449 cells transduced with a rAAV vector not containing FAC retained marked susceptibility to SV40 transformation.     

Long-term sweat collection using salt-impregnated pads

To facilitate a study of the pharmacokinetics of drugs dissolved in sweat, a technique was devised for collecting sweat at a steady rate over an 8-day period. Three normal subjects each wore 4 absorbent pads applied to their skin under waterproof dressings for 8 days. The absorbent pads were either plain cotton or cotton impregnated with sodium chloride crystals. Each pad (3 cm x 3 cm) was applied to an area of skin (2 cm x 2 cm) defined by an adhesive template, and was removed daily, weighed, and replaced, to determine progressive uptake of sweat. Sweat uptake by plain cotton pads reached a plateau value within 2 to 3 days and did not significantly increase thereafter; in contrast, uptake by the salt-impregnated pads continued at a steady rate for the full 8 days of the study (mean rate 0.79 mg/cm2/hr, SD = 0.16, N = 6). This effect may be related to an osmotic gradient across the skin, but the physiologic mechanisms are not completely clear. This appears to be a convenient tool for the collection of sweat over long periods at a steady rate.     

Effect of cholesterol and cholestyramine feeding and of fasting on sterol synthesis in the liver, lleum, and lung of the guinea pig

The effects of feeding diest containing either cholesterol (0.24% w/w) or cholestyramine (2.5% w/w) and of fasting on sterol synthesis in the liver, ileum, and lung of both male and female guinea pigs have been studied by measuring the incorporation by tissue slices of 14C-labeled acetate into total digitoninpredipitable sterols. Cholesterol feeding significantly decreased (P less than 0.05) sterol synthesis in the liver, ileum, and lung of the males and in the ileum of females. Cholestyramine feeding stimulated the rate of hepatic sterol synthesis 13-fold but did not significantly affect sterologenesis in the ileum. Sterol synthesis in the lung was significantly increased (P less than 0.05) but to a much lesser extent than in the liver. Fatty acid synthesis in the liver, ileum, and lung was not significantly affected by either cholesterol or cholestyramine feeding. In guinea pigs fasted for 24 hr, sterol synthesis was inhibited in all three tissues, the most pronounced effect occurring in the liver. Only in the lung was fatty acid synthesis significantly decreased (P less than 0.001) by fasting. Cholesterol feeding resulted in increased concentrations of cholesterol in the plasma and liver. Cholestyramine feeding reduced plasma cholesterol concentration by 81% in females and by 64% in males. However, it did not significantly change the tissue cholesterol concentrations. Fasting resulted in a significant increase (P less than 0.05) in plasma cholesterol concentration but did not effect the concentration of cholesterol in the tissues. It was concluded that in the normal guinea pig, the feedback inhibition produced by both cholesterol and also possibly by bile acids suppresses sterol synthesis in the liver to very low rates compared to those in the small intestine, where sterologenesis is not only less sensitive to the cholesterol negative feedback system than that in the liver, but also is not subject to regulation by the bile acid negative feedback system.     

Colitis cystica profunda

Colitis cystica profunda is a benign disease of the colon. Its importance lies in differentiating it from mucus-producing adenocarcinoma. It has rarely been described in the surgical literature. A review of records of patients seen at the Mayo Clinic produced 66 clinical cases of localized colitis cystica profunda, and in 21 patients the diagnosis was confirmed histologically. Follow-up, which was available in all patients, ranged from 2 months to 29 years, with a mean follow-up of more than 8 years. The data suggest that local excision is the preferred initial therapy.     

"Surprisingness" and short-term retention in pigeons.

Trained 14 Silver King pigeons in a symbolic matching-to-sample task in which food (access to grain) and no-food (blackout) samples were used. Responding to red test stimuli was reinforced on food sample trials, and responding to green test stimuli was reinforced on no-food sample trials. Samples of food and no food were rendered "expected" or "surprising" during subsequent testing by preceding samples with a previously established signal for either food (CS+) or no food (CS–). CS+ preceded food samples and CS– preceded no-food samples on surprising trials. Findings suggest that enhanced retention on surprising trials was apparent from the outset of testing to the extent that (a) surprising and expected trials were not markedly dissimilar to the trials of training, and (b) control over test responding by the CSs presented on expected and surprising trials was minimized. Results are discussed with regard to generalization decrement and directed remembering. It is concluded that surprising samples receive enhanced postperceptual processing and that the mechanism involved is that of retrieval-generated priming of short-term memory. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analysis of three restriction fragment length polymorphisms in the human type II procollagen gene

Cloned genomic DNA sequences corresponding to various regions of the human type II procollagen gene were used to analyze the DNA from 78 normal volunteers. Southern hybridization experiments detected polymorphic HindIII, BamHI, and EcoRI sites. The presence of the polymorphic HindIII site results in a 7.0-kilobase (kb) band, and the absence of this site results in a 14.0-kb band. When present, the BamH1 polymorphic site yields a 4.8-kb band, and when absent, yields a 7.2-kb band. The presence of the EcoRI polymorphic site results in a 3.7-kb band, and its absence results in a 7.0-kb band. Each polymorphic site was mapped. Analyses of the data demonstrated that the sites are present in overall gene frequencies of .39 for HindIII, .04 for BamHI, and .02 for EcoRI. Gene frequencies of the polymorphic sites were also studied with respect to race. The polymorphic sites are present in a Hardy-Weinberg distribution in the study population. Study of an extended family demonstrated that the segregation of the HindIII polymorphic site is consistent with Mendelian inheritance.