The rotifer trap of Zoophagus

The predacious watermold Zoophagus insidians traps loricate rotifers on short, lateral branches of the main, hyphal axis. These branches or traps are packed at their distal ends with a number of vesicles filled with an electron-dense matrix. Electron micrographs of the mycelium disclose a two-layered wall; the outer layer is electron dense and the inner, electron transparent. The outer dense layer on the tip of the trap is organized into a number of fine ridges and occasional discontinuities. Thin sections through recently trapped rotifers indicate that the cilia of the animals are stuck to the trap by a glue. This adhesive is derived from secretion of the matrix of the vesicles aggregated in the tip of the trap. The secretion mechanism is triggered by the animal and is accompanied by: 1. The separation of the two layers of the wall, 2. fusion of the vesicles with the cell membrane and 3. extrusion of the glue through pits in the tip of the inner wall of the trap. After snaring a rotifer, the previously arrested branch grows as a haustorium into the body cavity of the animal. The host tissues disintegrate within a few hours and appear to be the main nutrient source of the fungus.     

Eine zwergei-schale vom huhn

Zusammenfassung Es wird die Schale eines Zwergeies vom Huhn beschrieben. Kalkschale und Schalenmembran sind — an der Größe des Eies gemessen —dicker als gewöhnlich, und dazu erwies sich der Aufbau der mucoidreichen Schalenmembran als ungemein dicht. Bei der Entwicklung des Zwergeies setzte zunächst normale Schalenbildung ein, welche die Eisosphäriten, die Kegel und den unteren Abschnitt der Säulen lieferte. Dann aber kam es, vermutlich durch Pberangebot von Kalk, zur massenhaften Bildung von Calcosphäriten, zur Entstehung der Konglomeratschicht. Weiter verlängern sich Einzelkristalle der Konglomeratschicht unter lateraler Wachstumsbeschränkung zu aufrecht stehenden, dicht aneinanderschließenden Stelen Von den Kegeln bis zur Schalenoberfläche treten in allen Schichten Hyalosphariten auf, die als Anzeichen gestörter Schalenentwicklung gelten dürfen. Die Schale des Zwergeies enthält in allen Schichten des Exosphäriten Protoporphyrin, das sich an seiner typischen Rotfluorescenz zu erkennen gibt; insbesondere häuft es sich in der Konglomeratschicht an, bald in den Kalk aufgenommen, bald in unverkalkte organische Substanz zwischen den Kristallen eingebettet. Die zahlreichen Höckerchen des Zwergeies entstehen teils durch lokale Anhäufung von Hyalosphariten, teils aber als Extrusionen.

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Summary The shell of a dwarf-egg from the hen will be described. The calcitic shell and its membrane — in relation to the egg size — are thicker than normally; farther the structure of the shell membrane, reach on mucoid presents an exceeding density. In the development of the dwarf-egg first the normal shell production began, which supplied the eisospherites, the cones and the basal part of the columns. But then, probably effected by an abounded offer of calcite, the formation of numerous calcite spherites began, the conglomerate layer arised. Farther under lateral growth limitation monocrystals of the conglomerate layer lengthened to vertically orientated steles. In all layers of the exospheritic shell hyalospherites appear; they could be concerned as a symptom of disturbed shell formation. The shell of the dwarf-egg contains in all layers of the exospherite protoporphyrin granules, cognoscible by their typical red fluorescence. Especially the porphyrin is accumulated in the conglomerate layer, included in the calcite or embedded in the organic substance between the crystals. The numerous humps of the dwarf-egg arise partly by local aggregation of hyalospherites but partly as extrusions.

     

Über die „Stipeln“ vonRhytidophyllum Mart. (Gesneriaceae)

Zusammenfassung Die vielfach als Stipeln angesprochenen basalen Blattanhänge einiger Taxa der GesneriaceengattungRhytidophyllum Mart. können nicht als solche gelten, da ihnen wesentliche Merkmale echter Stipeln fehlen, insbesondere konstante Ausbildung bzw. Auftreten in der Blattfolge, praekursive Anlegung und proleptische Entwicklung. Gleichwohl sind sie aber als Bildungen des Blattgrundes zu betrachten und daher als vaginale Öhrchen im Sinne vonWeberling zu bezeichnen. Die bei manchen Taxa auftretenden sitzenden Laubblätter mit verbreiterter, teilweise stengelumfassender Blattbasis werden durch laubige Verbindung von Blattspreite und Öhrchen erklärt.Infolge Fehlens echter Stipeln bildet somitRhytidophyllum keine Ausnahme hinsichtlich der Blattgestaltung unter den Tubifloren.

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About the stipules ofRhytidophyllum Mart. (Gesneriaceae)

Summary The foliar appendages at the base of the short petiole in some taxa ofRhytidophyllum are often called stipules. But this term is not applicable, because these appendages lack important characteristics of true stipules, f. i. constancy in form and appearence during leaf succession, early ontogenetic origin and prolepsis. Nevertheless they are effigurations of the leaf base (Unterblatt) and have therefore to be regarded as vaginal auricules in the sense ofWeberling. The sessile and partially sheating leaves in someRhytidophyllum taxa result from foliar connections between lamina and auricules.Because of the absence of true stipulesRhytidophyllum fits well into the general leaf morphology of Tubiflorae.

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Herrn Prof. Dr. W.Leinfellner und Herrn Prof. Dr. F.Ehrendorfer danke ich für die Durchsicht des Manuskripts.     

Enzymatic semisynthesis of aprotinin homologues mutated in P′ positions

The replacement of amino acids in the P₁ and P₂ position of aprotinin, the bovine pancreatic trypsin inhibitor, is described. Using the modified inhibitor as starting material, with the hydrolyzed reactive-site peptide bond Lys¹⁵-Ala¹⁶, the residues P₁ (Ala¹⁶) and P₂ (Arg¹⁷) were split off by the action of aminopeptidase K. Incorporation of suitable dipeptides containing a basic residue (Lys or Arg) in the C-terminal position was carried out in a one pot reaction involving trypsin-catalyzed coupling. In this way, the native fragment Ala¹⁶-Arg¹⁷ was reintroduced and also replaced by Gly-Arg, Ala-Lys, and Leu-Arg yielding intact inhibitor molecules. The mechanism for incorporation of dipeptides was investigated by treating the aprotinin derivative with the Arg¹⁷-Ile¹⁸ peptide bond hydrolyzed with trypsin under proteosynthetic conditions. We established that only inhibitor molecules cleaved between Lys¹⁵ and Xaa¹⁶ are intermediates leading to the desired products. The inhibitory properties of the new aprotinin homologues were tested, and the significance of the P₁ residue for the inhibition of trypsin, kallikrein, and chymotrypsin was deduced.     

Elementary movement detectors in an insect visual system

In the theoretical part of the present work the input-output relation for a multi-input system is developed into a functional power series. This is formally equivalent to a decomposition of the system into a sum of all possible combinations of 1-, 2-, 3-... input subsystems. The average response of the system to a uniformly moving patern is known to be a Fourier series with respect to spatial frequency. The coefficients of the series are linear combinations of the weights by which different subsystems contribute to the total reaction. If a system can be shown to have essential nonlinearities of no higher than second order it is possible to calculate, from a Fourier analysis of the average movement response, the weight by which the nonlinear interaction between any two input elements contributes to the total reaction. This interaction is termed elementary movement detector. By the analysis presented here the arrangement of the elementary movement detectors may be determined for a two-dimensional array of input elements and the strength of their contributions to the total movement reaction may be calculated. Special experimental methods have been developed which allow one to apply this analysis to the visual system of the fruitfly Drosophila. The preliminary data presented show that the direction sensitive optomotor response of Drosophila can be attributed predominantly to the contributions from two elementary movement detectors which interconnect neighbouring visual elements. The detectors are oriented in the hexagonal array of the compound eye at +30° and at-30° with respect to the horizontal line of symmetry. A weak contribution from a detector between neighbouring elements along the horizontal line of symmetry is suggested by the present data. In the course of the analysis the contrast transfer properties of the compound eye are characterized.     

Model predictions of the ionic mechanisms underlying the beating and bursting pacemaker characteristics of molluscan neurons

The general properties of the excitable membrane on molluscan pacemaker neurons can be described on the basis of a fair amount of experimental evidence available in the literature. The neuronal membrane exhibits under voltage clamp an initial inward current carried by both Na⁺ and Ca²⁺ ions, the time- and voltage-dependent characteristics of which are similar to that of other excitable structures. The conductance mechanism for the two ion species and the transport kinetics appear to be closely similar. The time course and amplitude of the delayed outward current carried by K⁺ ions shows a marked dependence on the membrane potential. Characteristic for the molluscan neurons is the existence of an additional fast transient outward current which is only activated by hyperpolarizing shifts from the membrane potential. A regular beating discharge over a wide range of frequencies can be predicted by making the assumption of a metabolically controlled driving of the Na⁺ conductance. Bursting pacemaker characteristics can be correctly simulated by the model if sinusoidal variations of an additional Na⁺ and Ca²⁺ conductances g _Na and g _Ca, and periodic variations of the K⁺ conductance g _K, governed by the known operation of a metabolic substrate cycle are introduced. The close approximation of experimentally observed impulse bursts requires that the actual inpulse-frequency and the amplitude of the after-spike hyperpolarization are determined by the temporal pattern of g _Na, while the spike amplitude is controlled by g _Na which (although of similar time course) is lagging in phase behing g _Na. The periodic changes in additional K⁺ conductance g _K, are responsible for burst termination and the changes in inter-burst interval, to the effect that spike doublets, triplets and multi-spike bursts can be simulated by a suitable choice for the time characteristics of g _K. The model makes use of the finding that the Ca²⁺ inflow associated with a spike discharge actually activates g _K, so that large postburst hyperpolarizations can be obtained in high-frequency bursts.Supported by the Deutsche Forschungsgemeinschaft (Grant Ch 25/1)     

Gender-related differences in carnosine,anserine and lysine content of murine skeletal muscle

Summary. The aminoacyl-imidazole dipeptides carnosine (-alanyl-L-histidine) and anserine (-alanyl-1-methyl-histidine) are present in relatively high concentrations in excitable tissues, such as muscle and nervous tissue. In the present study we describe the existence of a marked sexual dimorphism of carnosine and anserine in skeletal muscles of CD1 mice. In adult animals the concentrations of anserine were higher than those of carnosine in all skeletal muscles studied, and the content of aminoacyl-imidazole dipeptides was remarkably higher in males than in females. Postnatal ontogenic studies and hormonal manipulations indicated that carnosine synthesis was up-regulated by testosterone whereas anserine synthesis increased with age. Regional variations in the concentrations of the dipeptides were observed in both sexes, skeletal muscles from hind legs having higher amounts of carnosine and anserine than those present in fore legs or in the pectoral region. The concentration of L-lysine in skeletal muscles also showed regional variations and a sexual dimorphic pattern with females having higher levels than males in all muscles studied. The results suggest that these differences may be related with the anabolic action of androgens on skeletal muscle.     

Basolateral membrane potassium conductance of A6 cells

Summary To study the properties of the basolateral membrane conductance of an amphibian epithelial cell line, we have adapted the technique of apical membrane selective permeabilization (Wills, N.K., Lewis, S.A., Eaton, D.C., 1979b, J. Membrane Biol. 45:81–108). Monolayers of A6 cells cultured on permeable supports were exposed to amphotericin B. The apical membrane was effectively permeabilized, while the high electrical resistance of the tight junctions and the ionic selectivity of the basolateral membrane were preserved. Thus the transepithelial current-voltage relation reflected mostly the properties of the basolateral membrane. Under basal conditions, the basolateral membrane conductance was inward rectifying, highly sensitive to barium but not to quinidine. After the induction of cell swelling either by adding chloride to the apical solution or by lowering the osmolarity of the basolateral solution, a large out-ward-rectifying K⁺ conductance was observed, and addition of barium or quinidine to the basolateral side inhibited, respectively, 82.4±1.9% and 90.9±1.0% of the transepithelial current at 0 mV. Barium block was voltage dependent; the half-inhibition constant (K _i) varied from 1499±97 m at 0 mV to 5.7±0.5 m at –120 mV.Cell swelling induces a large quinidine-sensitive K⁺ conductance, changing the inward-rectifying basolateral membrane conductance observed under basal conditions into a conductance with outward-rectifying properties.     

1H, 13C and 15N NMR assignments and solution secondary structure of rat Apo-S100β

Summary The ¹H, ¹³C and ¹⁵N NMR assignments of the backbone and side-chain resonances of rat S100 were made at pH 6.5 and 37°C using heteronuclear multidimensional NMR spectroscopy. Analysis of the NOE correlations, together with amide exchange rate and ¹H, ¹³C and ¹³C chemical shift data, provided extensive secondary structural information. Thus, the secondary structure of S100 was determined to comprise four helices (Leu³-Ser¹⁸, helix I; Lys²⁹-Leu⁴⁰, helix II; Gln⁵⁰-Glu⁶², helix III; and Phe⁷⁰-Ala⁸³, helix IV), four loops (Gly¹⁹-His²⁵, loop I; Ser⁴¹-Glu⁴⁹, loop II; Asp⁶³-Gly⁶⁶, loop III; and Cys⁸⁴-Glu⁹¹, loop IV) and two -strands (Lys²⁶-Lys²⁸, -strand I and Glu⁶⁷-Asp⁶⁹, -strand II). The -strands were found to align in an antiparallel manner to form a very small -sheet. This secondary structure is consistent with predictions that S100 contains two helix-loop-helix Ca²⁺-binding motifs known as EF-hands. The alignment of the -sheet, which brings the two EF-hand domains of S100 into close proximity, is similar to that of several other Ca²⁺ ion-binding proteins.     

Modeling the electrical behavior of anatomically complex neurons using a network analysis program: Passive membrane

We describe the application of a popular and widely available electrical circuit simulation program called SPICE to modeling the electrical behavior of neurons with passive membrane properties and arbitrarily complex dendritic trees. Transient responses may be calculated at any location in the cell model following current, voltage or conductance perturbations at any point. A numbering method is described for binary trees which is helpful in transforming complex dendritic structures into a coded list of short cylindrical dendritic segments suitable for input to SPICE. Individual segments are modeled as isopotential compartments comprised of a parallel resistor and capacitor, representing the transmembrane impedance, in series with one or two core resistors. Synaptic current is modeled by a current source controlled by the local membrane potential and an alpha-shaped voltage, thus simulating a conductance change in series with a driving potential. Extensively branched test cell circuits were constructed which satisfied the equivalent cylinder constraints (Rall 1959). These model neurons were perturbed by independent current sources and by synaptic currents. Responses calculated by SPICE are compared with analytical results. With appropriately chosen model parameters, extremely accurate transient calculations may be obtained. Details of the SPICE circuit elements are presented, along with illustrative examples sufficient to allow implementation of passive nerve cell models on a number of common computers. Methods for modeling excitable membrane are presented in the companion paper (Bunow et al. 1985).     

Plastommutationen nach R?ntgenbestrahlung vonArabidopsis Thaliana (L) Heynh.

Zusammenfassung Nach Röntgenbestrahlung vonArabidopsis thaliana wurde in der X₁-Generation auf Grund einer intraindividuellen Musteranalyse sowie entsprechender Kreuzungen eine gesicherte Erhöhung der Rate von plasmonisch bedingten Blattfarbveränderungen festgestellt. Bei der Mehrzahl dieser X₁-Pflanzen waren die mutierten, zumeist weißen Gewebe sektorialchimärisch angeordnet; Schecken, wie sie durch eine zufallsgemäße Entmischung erblich verschiedener Plastiden entstehen, fanden sich nur in 8,3% aller Fälle. Verschiedene der induzierten Formen konnten durch einen cytologischen Nachweis von Plastiden-Mischzellen als Plastom-Mutanten identifiziert werden. Insgesamt stieg die Häufigkeit der sicher erwiesenen Fälle von Plasmonabänderungen im Mittel zweier Versuche von einer Spontanrate um max. 0,07 nach Samenbestrahlung auf 1,95 und nach einer Bestrahlung von Zygoten auf 0,95. Damit wurde erstmalig die Möglichkeit aufgezeigt, auchdie Mutationshäufigkeit extrachromosomaler Erbstrukturen durch eine Röntgenbestrahlung zu erhöhen.Mit 5 TextabbildungenHerrn Professor Dr. A.Scheibe zum 60. Geburtstag gewidmet.     

Novel actions of ryanodine and analogues—Perturbers of potassium channels

The effects of ryanodine, 9,21-didehydroryanodine and 9,21-didehydroryanodol on two types of K⁺ channel (a maxi, Ca²⁺-activated, 170 pS channel (BK channel) and an inward rectifier, stretch-sensitive channel of 35 pS conductance (IK channel) found in the plasma membrane of locust skeletal muscle have been investigated. 10^–9M-10^–5M ryanodine irreversibly induced a dose-dependent reduction of the reversal potential (V_rev) of the currents of both channels, i.e. from 60 mV in the absence of the alkaloid to 15 mV for 10^–5M ryanodine, measured under physiologically normal K⁺ and Na⁺ gradients. In both cases the change in the ionic selectivity was Ca²⁺-independent. 9,21-didehydroryanodine and 9,21-didehyroryanodol also reduced V_rev, but only to 35 mV during application of 10^–5M of these compounds. Additionally, 9,21-didehydroryanodine reversibly diminished the conductances of the two K⁺ channels. To test the hypothesis that ryanoids increase Na⁺ permeability by enlarging the K⁺ channels, the channels were probed with quaternary ammonium ions during ryanoid application. When applied to the cytoplasmic face of inside-out patches exised from locust muscle membrane, TEA blocked the K⁺ channels in a voltage-dependent fashion. The dissociation constant (K_d(0)) for TEA block of the IK channel was reduced from 44 mM to 1 mM by 10^–7 M ryanodine, but the voltage-dependence of the block was unaffected. Qualitatively similar data were obtained for the BK channel. Ryanodine had no effect on the K_d for cytoplasmically-applied TMA. However, the voltage-dependence for TMA block was increased for both K⁺ channels, from 0.47 to 0.8 with 10^–6M ryanodine. The effects of ryanodine on TEA and TMA block support the hypothesis that ryanodine enlarges the K⁺ channels so as to facilitate permeation of partially hydrated Na⁺ ions.     

Regulation of shoot/root ratio by cytokinins from roots inUrtica dioica: Opinion

According to current knowledge, cytokinins are predominantly root-born phytohormones which are transported into the shoot by the transpiration stream. In the hormone message concept they are considered the root signals, which mediate the flux of the photosynthates to the various sinks of the plant. In this review, experiments are assessed, in which changes of the shoot to root ratio of biomass, caused by different levels of nitrogen supply to a model plant,Urtica dioica, could be traced to the natural cytokinin relations of the plant. Disturbance of the internal cytokinin balance of the plant resulted in a disproportionate distribution of the assimilates in favour of the cytokinin-enriched shoot. Inspite of some shortcomings of the hormone message concept, the presented work corroborates the significance of root-sourced cytokinins in the regulation of biomass partitioning between shoot and root.     

The concepts of scaling and refractoriness in psychophysical theories of vision

Summary In the context of the quantum theory of vision scalers, coincidence scalers, adapting coincidence scalers and dead time mechanisms have been used as basic constituents of network models: van de Grind et al. (1970a), Koenderink et al. (1970a, b). The possibilities that these devices offer to construct network models of vision are presently further analysed. First of all a mechanistic analysis is given of the event rate reduction characteristics of dead time boxes. Next the interaction of these devices with scalers is discussed in relation with a number of fluctuation models of vision proposed in the literature. A critical evaluation of these fluctuation models shows an important defect of most of them, viz. that unrealizable detection criteria are postulated. Our reconsideration of this detection problem then leads to the proposal of some specific realizable detectors. An application of the developed theory of mechanisms (machines) to the explanation of the flash detection characteristics of Limulus concludes the paper. Applications of the presented ideas to neural theory and modelling are treated hi a separate paper (van de Grind et al., 1970b) and for applications of the theory to psychophysically oriented visual modelling studies the reader is referred to Koenderink et al. (1970a, b) and van de Grind et al. (1970a).     

Transport-dependent alterations of membrane properties of mammalian colon measured using impedance analysis

Summary Direct current (DC) measurement methods have been commonly used to characterize the conductance properties of the mammalian colon. However, these methods provide no information concerning the effects of tissue morphology on the electrophysiological properties of this epithelium. For example, distribution of membrane resistances along narrow fluid-filled spaces such as the lateral intercellular spaces (LIS) or colonic crypts can influence DC measurements of apical and basolateral membrane properties. We used impedance analysis to determine the extent of such distributed resistance effects and to assess the conductance and capacitance properties of the colon. Because capacitance is proportional to membrane area, this method provides new information concerning membrane areas and specific ionic conductances for these membranes.We measured transepithelial impedance under three conditions: (1) control conditions in which the epithelium was opencircuited and bathed on both sides with NaCl–HCO₃ Ringer's solutions, (2) amiloride conditions which were similar to control except that 100 m amiloride was present in the mucosal bathing solution, and (3) mucosal NaCl-free conditions in which mucosal Na and Cl were replaced by potassium and sulfate or gluconate (K⁺ Ringer's). Three morphologically-based equivalent circuit models were used to evaluate the data: (1) a lumped model (which ignores LIS resistance), (2) a LIS distributed model (distributed basolateral membrane impedance) and (3) a crypt-distributed model (distributed apical membrane impedance). To estimate membrane impedances, an independent measurement of paracellular conductance (G _s ) was incorporated in the analysis. Although distributed models yielded improved fits of the data, the distributed and lumped models produced similar estimates of membrane parameters. The predicted effects of distributed resistances on DC microelectrode measurements were largest for the LIS-distributed model. LIS-distributed effects would cause a 12–15% underestimate of membrane resistance ratio (R _a /R _b ) for the control and amiloride conditions and a 34% underestimate for the K Ringer's condition. Distributed resistance effects arising from the crypts would produce a 1–2% overestimate ofR _a /R _b .Apical and basolateral membrane impedances differed in the three different experimental conditions. For control conditions, apical membrane capacitance averaged 21 F/cm² and the mean apical membrane specific conductance (G _a-norm) was 0.17 mS/F. The average basolateral membrane capacitance was 11 F/cm² with a mean specific conductance (G _b-norm) of 1.27 mS/F.G _a-norm was decreased by amiloride or K⁺ ringer's to 0.07 mS/gmF and 0.06 mS/F, respectively. Basolateral conductance was also reduced by amiloride, whereas capacitance was unchanged (G _b-norm=0.97 mS/F). For the K⁺ Ringer's condition, both basolateral conductance and capacitance were greatly increased such thatG _b-norm was not significantly different from the control condition.     

Scanning electron microscopy of primary membrane bone

Summary The organization and the development of primary bone were studied in a number of newborn or foetal mammals. Specimens were derived from long bones, calvaria and mandibles. The surface of the mineral component was exposed by treatment with an organic solvent (hot 1,2 ethane diamine or cold sodium hypochlorite solution) and in the case of some internal surfaces (endosteal surfaces of long bone shafts, endocranial aspects of calvaria and the lining of the dental groove or crypts of mandibles) some success was achieved in dissecting the soft tissues from the bone matrix surface. These surface were studied by scanning electron microscopy. Ground sections of similar material were studied by microradiography.Primary membrane bone was found to be most different from adult lamellar bone on rapidly growing (periosteal) surfaces and in the following respects. 1) Mineralization of both the ground substance and collagen occured close to the mineralizing front, so that a higher level was reached rapidly and without a maturation phase. 2) The mineral clusters at the mineralizing front did not reflect the collagen fibre distribution. 3) The collagen fibre bundles at the matrix surface, at least at internal surfaces, were irregular in size and random in orientation.Mineralizing fronts intermediate in character between those of rapidly forming, periosteal primary bone and adult lamellar bone were found on the uncommon internal forming surfaces and in the walls of vascular channels.Most internal surfaces were resorbing. There was a wide range in the size of the resorption lacunae — the many which were only as large as the osteocyte lacunae exposed by the resorption process may have been caused by uninucleated cells.This work has been supported by a grant from the Medical Research Council. The Stereoscan scannning electron microscope was provided by the Science Research Council, and the microradiographic equipment by Mr. R. V. Ely and the Ely-Webster trust. We would like to thank Mr. P. S. Reynolds, Miss A. J. Sutton and Mr. P. F. Farmer for technical and photographic assistance and Mrs. Jeanne Mills for secretarial assistance.     

A mode control model of a neuron's axon and dendrites

The ability of a neuron network to process information depends upon the ability of the individual neurons to transport impulses and to control the signal transport process in other neurons. The transport process for the action potential seen at the axon depends upon the excitable characteristic of the neural membrane. Propagation of signals in the dendrites, where synaptic imputs are most likely processed, is not clearly understood. Extracellular recordings of dendritic systems indicate that the dendrites are partially excitable and can conduct spikes. Further, electrical stimulation of the reticular formation or specific thalamic nuclei suggest that the conduction process can be modified in the dendrites of cortical cells.A Mode Control model is described which demonstrates many of the observed transport and control properties of dendrite and axon membrane. The model is based upon a simple extension of Fitzhugh's BVP model. Lateral transport over the membrane has been introduced by applying Kirchhoff's laws. Reinterpreting the variables, the influence of membrane potential, pH, and calcium ions can be identified. Modification of the voltage-current characteristic of the membrane model can change the axon model to a dendrite model. The dendrite model possesses a diffusion equation mode, a wave equation mode and a pulse mode. Signals are transferred in the wave and pulse mode and blocked in the diffusion mode. The dendrite's mode is controlled by the resting depolarization level. Experimental evidence tends to confirm these phenomena.The work described in this paper was performed while attending the University of California, Berkeley, under a National Institutes of Health Traineeship.     

Voltage-gated cation conductance channel from fragmented sarcoplasmic reticulum: Steady-state electrical properties

Summary The interaction of fragmented sarcoplasmic reticulum (SR) with an artificial planar phospholipid membrane under conditions known to induce fusion of phospholipid vesicles raises the conductance of the planar bilayer by several orders of magnitude. Measurements of steady-state electrical properties of bilayers thus modified by SR show that two types of conductance pathways are present. One is a voltage-independent pathway which may be somewhat anion-selective. The other is a voltagegated ionophore showing selectivity to small monovalent cations. This latter ionophore is fully oriented within the artificial bilayer and is inhibited asymmetrically by divalent cations. It is also inhibited below pH 6. The ionophore displays single-channel conductance fluctuations between two states, open and closed, with an open-state conductance of 1.4×10^–10 mho in 0.1m K⁺. The physiological function of this ionophore is unknown.     

Production and characterization of monoclonal IgM autoantibodies specific for the T-cell receptor

Natural autoantibodies to the T-cell receptor (Tcr) have been identified in all human sera. However, titer, epitope specificity, and isotype vary with physiological conditions, autoimmune diseases, and retroviral infections. The levels of anti-Tcr autoantibodies in rheumatoid arthritis (RA) patients are significantly higher than in normal individuals, and the autoantibodies are typically IgM. To obtain detailed information on these autoantibodies, we generated B-cell heterohybridomas secreting monoclonal IgM autoantibodies (mAAbs) from the synovial tissue and peripheral blood of RA patients. We selected clones secreting mAAbs that bound a major V epitope defined by a synthetic peptide that contains the CDR1 region of the V 8.1 gene product. From these we isolated a subset of seven mAAbs that bound a recombinant single-chain V/V construct containing the peptide epitope and, also to JURKAT cells which express V 8.1. The mAAbs produced by these clones were distinct from each other in their V-region sequences. However, all the V regions were essentially identical to germline sequences in both the heavy and light chains. Heavy-chain CDR3 segments ranged in length from 17 to 26 residues, did not correspond to any known autoantibodies, and showed extensive N-region diversity in the V(D)J junctions. Five monoclonal autoantibodies use V_H 3 genes, while the remaining two utilized V_H 4 sequences. Light-chain variable regions used were V 3 (two), V 3 (four), and one V 2. These autoantibodies derived their unique features from their CDR3 segments that could not be aligned with any known sequences.     

Voltage dependence of the basolateral membrane conductance in theAmphiuma collecting tubule

Summary The basolateral potassium conductance of cells of most epithelial cells plays an important role in the transcellular sodium transport inasmuch as the large negative equilibrium potential of potassium across this membrane contributes to the electrical driving force for Na⁺ across the apical membrane. In the present study, we have attempted to establish, theI-V curve of the basolateral membrane of theAmphiuma collecting tubule, a membrane shown to be K⁺ selective. TransepithelialI-V curves were obtained in short, isolated perfused collecting tubule segments. The shunt conductance was determined using amiloride to block the apical membrane Na⁺ conductance. In symmetrical solutions, the shuntI-V curve was linear (conductance: 2.2±0.3 mS·cm^–2). Transcellular current was calculated by subtracting the shunt current from the transepithelial current in the absence of amiloride. Using intracellular microelectrodes, it was then possible to measure the basolateral membrane potential simultaneously with the transcellular current. The basolateral conductance was found to be voltage dependent, being activated by hyperpolarization: conductance values at –30 and –80 mV were 3.6±1.0 and 6.6±1.0 mS·cm^–2, respectively. BasolateralI-V curves were thus clearly different from that predicted by the constant field model. These results indicate that the K⁺-selective basolateral conductance of an amphibian collecting tubule shows inward (anomalous) rectification. Considering the electrogenic nature basolateral Na–K-pump, this may account for coupling between pump-generated potential and basolateral K⁺ conductance.