GABAB receptor activation desensitizes postsynaptic GABAB and A1 adenosine responses in rat hippocampal neurones

Whole-cell recordings of EPSCs and G-protein-activated inwardly rectifying (GIRK) currents were made from cultured hippocampal neurones to determine the effect of long-term agonist treatment on the presynaptic and postsynaptic responses mediated by GABA_B receptors (GABA_BRs). GABA_BR-mediated presynaptic inhibition was unaffected by agonist (baclofen) treatment for up to 48 h, and was desensitized by about one-half after 96 h. In contrast, GABA_BR-mediated GIRK currents were desensitized by a similar amount after only 2 h of agonist treatment. In addition, presynaptic inhibition mediated by A₁ adenosine receptors (A₁Rs) was unaffected by prolonged GABA_BR activation, whereas A₁R-mediated GIRK currents were desensitized. Desensitization of postsynaptic GABA_BR and A₁R responses was blocked by the GABA_BR antagonist (1-(S)-3,4-dichlorophenylethyl)amino-2-(S) hydroxypropyl-p-benzyl-phosphonic acid (CGP 55845A), but not by the A₁R antagonist cyclopentyldipropylxanthine (DPCPX). GIRK current amplitude could be partially restored after baclofen treatment by either coapplication of baclofen and adenosine, or intracellular infusion of the non-hydrolysable GTP analog 5'-guanylylimidodiphosphate (Gpp(NH)p). Short-term (4-24 h) baclofen treatment also significantly desensitized the inhibition of postsynaptic voltage-gated calcium channels by activation of GABA_BRs or A₁Rs. These results show that responses mediated by GABA_BRs and A₁Rs desensitize differently in presynaptic and postsynaptic compartments, and demonstrate the heterologous desensitization of postsynaptic A1R responses.     

Linkage relationships between the three phosphoglucomutase loci PGM1, PGM2 and PGM3

1. Phosphoglucomutase phenotypes have been studied in several generations of the family of an individual heterozygous at each of the three loci, PGM₁, PGM₂, and PGM₃. 2. PGM₁ and PGM₂ phenotypes were determined using red cells. Fibroblasts grown in tissue culture were used for PGM₃ phenotyping. 3. The family results support the genetical hypothesis based on the analysis of dizygotic twin pairs that the PGM₃ isozyme patterns found in the placenta are determined by two alleles, PGM¹₃ and PGM²₃. 4. Locus PGM₃ is not closely linked to locus PGM₂ 5. The data also support the previous findings that locus PGM₁ is not closely linked to PGM₂ or PGM₃.     

Reactivity to sodium tetrachloropalladate (Na2[PdCl4]) compared to PdCl2 and NiCl2 in lymphocyte proliferation tests

Background: For patch testing, replacement of the commonly used palladium dichloride (PdCl₂) by sodium tetrachloropalladate (Na₂[PdCl₄]) was recently demonstrated to improve test accuracy and show a significant correlation with nickel (Ni), supporting the concept of cross‐reactivity between Pd and Ni. A promising alternative to metal allergy patch testing is the in vitro lymphocyte proliferation test (LTT). Objectives: The aim of this study was to test whether Na₂[PdCl₄] is also more sensitive for diagnosing Pd allergy with a standardized LTT. Patients/methods: After determining optimal nontoxic and nonmitogenic concentrations for Na₂[PdCl₄], blood samples from 105 patients with clinical suspicion of metal allergy were tested with an LTT called memory lymphocyte immuno stimulation assay for Na₂[PdCl₄], PdCl₂ and NiCl₂. Reaction profiles were analysed for concordant positive reactions. Results: Using the conventional cut‐off of stimulation index ≥ 3, 74.3% showed a positive reaction to NiCl₂, 15.2% to PdCl₂ and 28.6% to Na₂[PdCl₄]. All positive results to PdCl₂ were covered by Na₂[PdCl₄]. From the 30 positive reactions to Na₂[PdCl₄], 26 (87%) were concordant for NiCl₂ reactivity. Conclusion: In LTT, the use of Na₂[PdCl₄] results in more positive reactions in Pd allergy testing which are in concordance with positive reactions to PdCl₂ and NiCl₂.     

Density Distribution Profiles of T Cells: TM, TG and TA Cells and Response Patterns in Autologous Versus Allogeneic MLRs

Discontinuous Percoll gradients have been used to obtain selected human peripheral blood T lymphocytes without having to resort to interactions with immune complexes in the fractionation of Tm, Tg and Ta cells. Here, we could show that Ta cells represent a heterogeneous population with no distinct density profile, in contrast to light (Tg) and heavy (Tm) cells. Enriched, heavy Tm cells could be shown to be excellent responders in allogeneic MLR while failing to react in autologous MLR. In contrast, T cells of light density preferentially respond in autologous compared with allogeneic MLR.     

O2 Delivery and the Venous PO2-O2 Uptake Relationship in Pump-Perfused Canine Muscle

Under the conditions of both an increased red cell affinity for O(2) at a constant rate of O(2) delivery (arterial O(2) content x flow) and a decrease in the rate of O(2) delivery induced by hypoxic hypoxia at constant blood flow, we have obtained a linear relationship between the partial pressure of O(2) in the muscle venous effluent (P(v,)(O(2))) and O(2) uptake (.V(O(2))). The relationship is described by the equation .V(O(2)) = D(a) x P(v,)(O(2)) + .V(O(2)conv)) where D(a) is the apparent O(2) diffusion capacity and .V(O(2)conv)) is O(2) delivery-limited .V(O(2)), and D(a) x P(v,)(O(2)) represents the O(2) diffusion-limited .V(O(2)) .V(O(2)diff)). From these observations, we propose the hypothesis that .V(O(2)) consists of two additive values, .V(O(2)conv)) and .V(O(2)diff)). The mechanism underlying the reduction in .V(O(2)) that is induced by reducing O(2) delivery to markedly below the .V(O(2)conv)) value has only been investigated using a model based on the single compartment of diffusion-limited .V(O(2)), and has not been investigated in terms of this additive .V(O(2)) model. The single compartment analysis appears to overestimate the role of O(2) diffusion in limiting the reduction of .V(O(2)) that occurs in response to a decrease in O(2) diffusion capacity, as reflected by the .V(O(2))/P(v,)(O(2)) ratio. To gain better insight into the mechanism involved, we altered the rate of O(2) delivery by changing arterial P(O(2)) from normoxia (with inhalation of air) to hypoxia (by inhalation of 10-11 % O(2)) and blood flow (with high and low flow rates (n = 7 for both groups), and very low and ischaemic flow rates (n = 4 for both groups)) in pump-perfused dog gastrocnemius preparations during tetanic isometric contractions at 1 Hz. As rates of O(2) delivery were reduced from 23.2 to 10.9 ml min(-1) (100 g)(-1), significant decreases in P(v,)(O(2)) and .V(O(2)) were observed (P < 0.05). From the data of P(v,)(O(2)) and .V(O(2)) values within this range of O(2) delivery rates, we obtained the regression equation .V(O(2)) = 0.22 x P(v,)(O(2)) + 8.14 (r = 0.58). From the equation, the intercept of the .V(O(2))-axis was significantly different from zero (P < 0.05), in accordance with the observation that the .V(O(2)) /P(v,)(O(2)) ratio (ml min(-1) (100 g)(-1) Torr(-1)) increased from 0.54 to 1.35 (P < 0.05). However, at extremely low rates of O(2) delivery (5.6 and 7.3 ml min(-1) (100 g)(-1) the .V(O(2))/P(v,)(O(2)) ratio was 1.51 and 2.80 (P < 0.05), respectively. This indicates a break in the linear .V(O(2))-P(v,)(O(2)) relationship as the rate of O(2) delivery was reduced to below the .V(O(2)conv)) value of the .V(O(2))-axis intercept. These results suggest that the reduction in .V(O(2)) caused by extreme reductions in the rate of O(2) delivery is not attributable to a reduction in O(2) diffusion capacity, as expected from the .V(O(2))/P(v,)(O(2)) ratio, but to a reduction in the O(2) delivery-limited .V(O(2)) component, as evaluated by the .V(O(2))-axis intercept of the linear .V(O(2))-P(v,)(O(2)) relationship.     

A comparison of the biochemical properties of the human diaphorase (DIA3) isozymes determined by the common alleles DIA13, DIA23 and DIA33

(1) Various buffer systems for the starch gel electrophoresis of human diaphorase isozymes have been explored. Electrophoresis in a Tris/Borate system at pH 8.6 which includes 70 micron NADH in the gel and cathodal electrode buffers, provides good resolution of the six DIA3 phenotypes previously resolved by isoelectric focusing. (2) The variant genes DIA13, DIA23 and DIA33 occur with frequencies of about 0.76, 0.23 and 0.01 respectively in the English population. (3) The isozymes determined by the least common gene, DIA33, are markedly different from the isozymes determined by DIA13 and DIA23 in their relatively low heat stability, high affinity for Blue Sepharose and slow anodal electrophoretic mobility in buffer systems containing borate. The DIA3 1 and DIA3 2 isozymes are similar to one another in these characteristics.     

Evidence for the assignment of the loci AK1, AK3 and ACONs to chromosome 9 in man

The segregation of human enzymes and chromosomes has been studied in more than 30 independent primary human-rodent somatic cell hybrids and a series of 64 subclones. The results strongly suggest that the locus determining AK1, 'red cell' adenylate kinase, is on chromosome 9 in man, and hence that the locus for the ABO blood groups and that for the Nail-patella syndrome may also be assigned to this chromosome. Evidence is presented indicating that another adenylate kinase, nucleoside triphosphate adenylate kinase, and also the soluble form of aconitase, are probably syntenic with AK1, and that the mitochondrial form of aconitase is probably not syntenic with these loci.     

Selective Functional Role of Murine TM and TG Cells in Concanavalin-A-Induced T-Cell Activation

Murine splenic cells were separated on Ig-anti-Ig columns to yield cell populations depleted of IgM-FcR (Fc receptor)-expressing (TM) and IgG-FcR-expressing (TG) cells and also cells expressing neither of these two FcR (TO). The proliferative response to the lectin concanavalin A (Con A) was shown to be present mainly in cell populations depleted of TM cells (T cells lacking IgM FcR)--that is, TM and TO. The low Con A response in the other cell populations, namely TG and TTOT, was due to a selection against T-cell growth factor (TCGF)-reactive cells, since TCGF production within these subsets was not impaired and the low proliferative response was not reconstituted by preformed TCGF. TG-cells were able to inhibit the Con-A-induced proliferation of TO and TM cells dose-dependently. These data strongly suggest the presence of a step-one regulatory, suppressive mechanism comprised within the TM population.     

Human alcohol dehydrogenase ADH1, ADH2 and ADH3 loci in a mixed population of Bahia, Brazil

1. The three structural gene loci of human alcohol dehydrogenase have been studied in liver, jejunum and lung from 300 newborns in a triracially mixed population of Bahia, Brazil. 2. The frequency of the ADH23 allele was 0-1392, suggesting that the ADH23 allele is less frequent in Negroes. 3. A new ADH2 variant was identified. The electrophoretic pattern was interpreted as due to a new allele which is provisionally called ADH2Bahia. 4. By electrophoretic classification the 'atypical' variant was found in 2-8% of the sample. A question is raised regarding the ancestral origin of the 'atypical' variant in the population. Because this variant is common in Japanese it may have reached the present day population of Bahia through their American Indian ancestors. 5. Subjective estimation of the proportions of beta chains by giving scores to the liver isozymes alphaalpha, alphabeta and betabeta showed a clear relationship between the fetal weight and the beta chain activity. 6. The proportion of beta chains in the liver is significantly less when there is no enzyme activity in the lung, indicating some synchronous 'turning on' mechanism for alcohol dehydrogenase synthesis in both tissues.     

An interpretation of human diaphorase isozymes in terms of three gene loci DIA1, DIA2 and DIA3

NADH and NADPH diaphorase isozymes have been studied in human tissues. Evidence from rare heterozygotes suggests that the red cell and main tissue forms of NADH diaphorase are products of the same locus DIA1. NADPH-dependent diaphorase appears to be the product of a second locus DIA2. A third locus, DIA3, codes for the polymorphic sperm diaphorase. The products of this locus are also found in foetal tissues including placenta and adult brain and gonads. The products of these three loci may be distinguished by their substrate specificity, thermostability and molecular size.     

Regulation of histamine release from human basophil leucocytes: role of H1, H2 and H3 receptors

A novel class of histamine receptors (H3), controlling histamine synthesis and release, was described in rat and human brain and peripheral nerve endings. The present study was undertaken to evaluate whether H3 receptors contribute to the regulation of histamine release from human basophils. Basophil leucocytes were incubated with a H3 antagonist (thioperamide; concentrations ranging from 1 nM to 10 microM) or with a H3 ((R)alpha methyl-histamine; concentrations ranging from 1 to 100 mM), and subsequently were stimulated with optimal doses of anti-IgE and formyl-methionyl-leucyl-phenyl-alanine (f-met peptide). No significant modifications of histamine release were observed after incubation either with the H3 agonist or with the H3 antagonist. By contrast, a H2 antagonist (cimetidine; concentrations ranging from 1 to 100 microM) exerted a dose-dependent enhancing effect on anti-IgE- and, to a lesser extent, on f-met peptide-induced histamine release. A H1 antihistamine (chlorpheniramine; concentrations ranging from 100 nM to 1 microM), at the highest concentration employed, displayed an inhibitory activity on IgE-dependent and IgE-independent histamine release. Exogenous histamine was shown to exert a dose-dependent inhibitory effect on two-staged anti-IgE-induced histamine release. Taken as a whole, these results suggest that H3 receptors are not involved in the regulation of histamine release from human basophils; by contrast, H2 receptors participate in controlling histamine release from human basophils, as previously demonstrated by other authors.     

Preferential Expression of VH5 and VH6 Immunoglobulin Genes in Early Human B-Cell Ontogeny

Two veto active allospecific cytotoxic T-cell clones (CTL), 4A2 and 4B3, were studied for the development of autoreactivity. The 4A2 CTL became autoreactive within 6 days when cultured without appropriate allospecific stimulator cells, whereas the 4B3 CTL retained its alloreactivity without becoming autoreactive when cultured under these conditions. Simultaneously with the development of autoreactivity, the 4A2 CTL lost its veto activity. Limiting dilution cultures of normal allospecific 4A2 CTL cells and autoreactive 4A2 CTL cells and mixtures of both showed that the former CTL cells were capable of inhibiting clonal growth of the autoreactive CTL cells in a dose-dependent manner. We suggest that this growth inhibition reflects veto activity, i.e. cells capable of growing are inhibited by autorecognition of veto active allospecific 4A2 CTL cells. Taken together, the present results indicate that the existence of intraclonal down-regulation of potentially autoreactive cells is a normal feature of allospecific cytotoxic T-cell clones.