Signal transduction in human B cells initiated via Ig{beta} ligation

Ig and Igß heterodimers are non-covalently associatedwith Ig to compose the antigen receptor complexes on B cells.The demonstration that different sets of tyrosine kinases bindto the cytoplasmic tails of Ig and Igß suggests thatIg and Igß may activate distinct second messengerpathways. In this study, we examined the effects of mAbs againstan exposed epitope of human Igß on pre-B and B celltriggering. Cross-linkage of Igß on B cells leadsto activation of tyrosine kinases, hydrolysis of phosphatidylinositides,and elevation of intracellular Ca²⁺, effects qualitatively identicalto those of anti-_µ mAbs. Our observations thus indicatethat cross-linking of Igß does not segregate signaltransduction pathways connected with the cytoplasmic talls ofIg and Igß. Ig ligation has been reported to be moreeffective in triggering pre-B than B cells, whereas our resultsindicated that Igß ligation is more efficient in triggeringB than pre-B cells. In addition to their activation properties,the anti-Igß mAbs effectively modulated B cell receptorcomplexes and blocked terminal differentiation of all plasmacell isotypes. The findings support the idea that anti-Igßcould serve as a universal B cell immunosuppressant.     

Mitochondrial genome variation and evolutionary history of Australian and New Guinean aborigines

To study the evolutionary history of the Australian and New Guinean indigenous peoples, we analyzed 101 complete mitochondrial genomes including populations from Australia and New Guinea as well as from Africa, India, Europe, Asia, Melanesia, and Polynesia. The genetic diversity of the Australian mitochondrial sequences is remarkably high and is similar to that found across Asia. This is in contrast to the pattern seen in previously described Y-chromosome data where an Australia-specific haplotype was found at high frequency. The mitochondrial genome data indicate that Australia was colonized between 40 and 70 thousand years ago, either by a single migration from a heterogeneous source population or by multiple movements of smaller groups occurring over a period of time. Some Australian and New Guinea sequences form clades, suggesting the possibility of a joint colonization and/or admixture between the two regions.     

Sulfonylurea-sensitive K+ channels and their probable role for the membrane potential of mouse motor nerve endings

We studied the effect of the K_ATP channel blockers tolbutamide and glibenclamide on presynaptic membrane currents in the mouse M. triangularis sterni preparation using the perineural recording technique. Both sulfonylureas blocked part of the fast K⁺ component within 2 min after application. The block was much more pronounced under glucose-free conditions and was completelyreversible by washing. Addition of glucose to glucose-free bath solution also reduced the K⁺ component. A further effect of the sulfonylureas was observed under glucose-free conditions. With a delay of 5 to 10 min, the nodal Na⁺ component began to diminish and disappeared within 30 min. This was associated with a dramatic increase in spontaneous quantal transmitter release suggesting that the block of sulfonylurea-sensitive K⁺ channels causes depolarization of motor nerve terminals and fibres thus inactivating Na⁺ channels. Tetraethylammonium (TEA) which blocks ATP-dependent K⁺ channels in high concentrations caused, under glucose-free conditions, the same delayed effect as the sulfonylureas. This delayed effect was fully reversible by washing with glucose-containing, but not with glucose-free solution. Our findings strongly suggest that K_ATP channels exist in mammalian motor nerve endings and that under hypoglycemic conditions these channels open and become essential for the maintenance of the membrane potential.     

Bestimmung der Bindung von Trijodthyronin an Serumproteine mittels Dextran-Gel-Filtration

Zusammenfassung 1. Es wird eine Methode zur gleichzeitigen Bestimmung des sog. freien und des proteingebundenen Anteils von in vitro zugesetztem L-Trijodthyronin-¹³¹Jod im Serum mittels Dextran-Gel-Filtration angegeben. In der beschriebenen Form ist diese Technik für die routinemäßige Anwendung in der Klinik zur Bestimmung der Bindungs- und Transportverhältnisse von Trijodthyronin geeignet.2. In sog. Verdrängungsversuchen wurde nichtmarkiertes Trijodthyronin dem Inkubationsgemisch von Serum und L-Trijodthyronin-¹³¹Jod zugesetzt. Die zugesetzten Trijodthyroninmengen erschöpfen die Gesamtbindungskapazität der Serumproteine in dem gewählten Konzentrationsbereich keineswegs. Im Gegensatz zum Verhalten der prozentualen Anteile des sog. freien und des proteingebundenen Trijodthyronins steigt die absolute Menge des proteingebundenen Trijodthyronins dabei steil an. Man findet eine Kurve, die nicht einer einfachen Sättigunskurve entspricht, sondern eine Resultante aus Sättigungskurven verschiedener Trijodthyronin-bindender Proteine und Verdrängungskurven kompetitiv gebundener Substanzen (z.B. Thyroxin) darstellt.3. Dextran-Gel wirkt nicht als einfaches Molekülsieb für Trijodthyronin. Es greift vielmehr durch Adsorptionsvorgänge kompetitiv in die Serumproteinbindungsverhältnisse des Trijodthyronins ein. Die physiologische Bedeutung des sog. freien Anteils an Trijodthyronin wird diskutiert.4. Die Methode zur Bestimmung des proteingebundenen Jods (PB¹²⁷I) mittels alkalischer offener Veraschung (Barker) wurde technisch vereinfacht und bezüglich ihrer Reproduzierbarkeit untersucht. Die¹³¹Jodausbeute aus zugesetztem L-Thyroxin-¹³¹Jod lag bei diesem Verfahren bei ca. 80%.

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Summary 1. A method allowing the simultaneous determination in serum of the socalled free and the protein bound part of 1-triiodothyronine-¹³¹I added in vitro, using dextran gel filtration, is presented. Assessment of serum protein binding and transport of triiodothyronine can be conveniently performed for clinical purposes by this procedure.2. In socalled discharge experiments non-labelled triiodothyronine is added to incubation mixtures of serum and l-triiodothyronine-¹³¹I. The amount of added triiodothyronine did not exhaust the total binding capacity of serum proteins for triiodothyronine. In contrast to the behaviour of the percentages of socalled free and protein bound triiodothyronine the absolute amount of protein bound triiodothyronine was rising linearly with rising concentrations of triiodothyronine added. The curve obtained was interpreted as resulting from saturation curves of different triiodothyronine binding proteins and discharge curves of competitively bound substances, e.g. thyroxine.3. Dextran gel is not acting merely as molecular sieve for triiodothyronine, but rather competing actively with serum proteins for triiodothyronine, adsorbing the latter. The physiological rôle of the socalled free triiodothyronine is discussed.4. With addition of l-thyroxine-¹³¹I 80% of¹³¹iodine was recovered, when the method ofBarker for determination of serum protein bound¹²⁷iodine (open alkaline ashing) was used.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft.

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Herrn Prof. Dr. Dr. h. c.Carl Krauspe in Verehrung zum 70. Geburtstag gewidmet.     

Vestibular responses in the Rhesus monkey ventroposterior thalamus. II. Vestibulo-proprioceptive convergence at thalamic neurons

Summary The vestibular thalamic relay in the Rhesus ventrobasal complex, identified in a previous field potential study (part I, Deecke et al., 1974), has now been investigated with neuronal recordings in the thalamus in order to clarify its functional role. In part I, short latency responses (2.5 msec) were found in the corner between VPL, VPM and VPI nuclei, largely including dorsal portions of the VPI nucleus. Field potentials of somewhat longer latency (4–5 msec) were recorded in VPL and in other thalamic nuclei, including the posterior nuclear group.Neuronal responses were recorded in thalamic nuclei of awake flaxedilized Rhesus monkeys. Cells not responding to vestibular stimulation (round window polarisation of either labyrinth) were ignored. The great majority (80%) of those neurons responding to labyrinth polarisation showed convergence with deep somatic (proprioceptive) input from joints and muscles of vertebral column and limbs. 60% of these bimodal neurons responded to movement of cervical joints. Very few vestibularly responsive cells received cutaneous (6.6%), non-optokinetic visual or auditory (2.6% each) input. Proprioceptive fields tended to be large, frequently involving more than one joint, and could be even bilateral. For a few cells the pattern of vestibulo-proprioceptive convergence could be fitted to a coordinated body position that might occur during normal locomotion. 78% of the cells responded to polarisation of both labyrinths, indicating strong bilateral projection.     

Performance characteristics of four immunoassays for antiepileptic drugs on the IMMULITE 2000 automated analyzer

Carbamazepine, phenobarbital, phenytoin, and valproic acid are commonly used antiepileptic drugs that show complicated pharmacokinetic behavior Nonisotopic immunoassays are used routinely to monitor these drugs, and assay specificity is important to obtain accurate results. By using samples from subjects receiving each of these antiepileptic medications, competitive immunoassays for them were evaluated on an IMMULITE 2000 automated chemiluminescent analyzer (Diagnostic Products, Los Angeles, CA). Phenytoin assays were evaluated using an additional set of samples from patients with abnormal renal function. All 4 methods were linear, had imprecision of less than 10%, and compared well with other commercial immunoassays. A positive bias was observed for phenytoin measured in samples from uremic patients compared with a high-performance liquid chromatography reference method. The molar cross-reactivity of carbamazepine-10,11-epoxide was 12% in the carbamazepine assay. Phenytoin metabolites and fosphenytoin had substantial cross-reactivity in the phenytoin assay. All antiepileptic drug assays performed well and are suitable for use in monitoring patients receiving antiepileptic drug therapy. One possible exception is the phenytoin assay with samples from patients with renal insufficiency.     

A chronic mouse model of Parkinson's disease has a reduced gait pattern certainty

The purpose of this investigation was to determine if a chronic Parkinson's disease mouse model will display less certainty in its gait pattern due to basal ganglia dysfunction. A chronic Parkinson's disease mouse model was induced by injecting male C57/BL mice with 10 doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (25 mg/kg) (MPTP) and probenecid (250 mg/kg) (P) over 5 weeks. This chronic model produces a severe and persistent loss of nigrostriatal neurons resulting in dopamine depletion and locomotor impairment. The control mice were treated with probenecid alone. Fifteen weeks after the last MPTP/P treatment, the mice were videotaped in the sagittal plane with a digital camera (60 Hz) as they ran on a motorized treadmill at a speed of 10 m/min. The indices of gait and gait variability were calculated. Stride length was significantly (p = 0.016) more variable in the chronic MPTP/P mice. Additionally, the chronic MPTP/P mice had a statistically less certain gait pattern when compared to the control mice (p = 0.02). These results suggest that variability in the gait pattern can be used to evaluate changes in neural function. Additionally, our results imply that disorder of the basal ganglia results in less certainty in modulating the descending motor command that controls the gait pattern.     

Genes for glycosylphosphatidylinositol toxin biosynthesis in Plasmodium falciparum

About 2.5 million people die of Plasmodium falciparum malaria every year. Fatalities are associated with systemic and organ-specific inflammation initiated by a parasite toxin. Recent studies show that glycosylphosphatidylinositol (GPI) functions as the dominant parasite toxin in the context of infection. GPIs also serve as membrane anchors for several of the most important surface antigens of parasite invasive stages. GPI anchoring is a complex posttranslational modification produced through the coordinated action of a multicomponent biosynthetic pathway. Here we present eight new genes of P. falciparum selected for encoding homologs of proteins essential for GPI synthesis: PIG-A, PIG-B, PIG-M, PIG-O, GPI1, GPI8, GAA-1, and DPM1. We describe the experimentally verified mRNA and predicted amino acid sequences and in situ localization of the gene products to the parasite endoplasmic reticulum. Moreover, we show preliminary evidence for the PIG-L and PIG-C genes. The biosynthetic pathway of the malaria parasite GPI offers potential targets for drug development and may be useful for studying parasite cell biology and the molecular basis for the pathophysiology of parasitic diseases.