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H Hatt

Publications and source records attributed to H Hatt.

86 records · Page 5Linked to original sources
PubMed1988

Ionic permeabilities of L-glutamate activated, excitatory synaptic channel in crayfish muscle.

Excitatory single channel currents triggered by L-glutamate were measured in outside-out excised patches of crayfish muscle membrane. If an 'intracellular' solution was present in the pipette and normal extracellular solution with added glutamate (10(-3) M) passed the outside of the patch, the single channel currents, i1, had amplitudes of -8 pA at a patch potential of -70 mV. If in the extracellular solution Na+ was replaced by Li+ or Ca2+, the amplitudes of single channel currents were reduced by about 30%. Only about 20% of the channel current amplitude remained on replacement of Na+ by choline. Replacement of Na+ reduced the variance of channel amplitude distributions to the level of the baseline. Presence of Na+ thus induces an additional variance of open channel current. When the proportions of Na+/choline were varied, the resulting channel currents could be separated in Na+, Ca2+ and choline components. The amplitude of the Na+ component, i1,Na, could be described by a constant channel permeability pi Na = 110 10(-15) cm3 s-1 according to the constant field equation. Ba2+ could replace Ca2+ without change in single channel current, while replacement of Ca2+ by Mg2+ reduced the channel currents by 20%. The following permeabilities of the single channel were estimated (in 10(-15) cm3 s-1): pi Na = 110, pi K = 86, pi Ca = 30, pi Mg = 24, pi Ba = 30, pi Li = 84 and pi choline = 11. These permeabilities were obtained inserting ionic concentrations. The respective permeabilities are listed also as calculated on the basis of ionic activities.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Calcium dependent gating of the L-glutamate activated, excitatory synaptic channel on crayfish muscle.

Excitatory, glutamate-activated single channel currents were measured in outside-out patches of crayfish muscle. The open times of single channel openings, and the durations and rates of bursts were evaluated. These kinetic parameters were not appreciably affected by replacement of extracellular Na+ by Li+ or choline. Changes in extracellular Ca2+ concentration Cao also did not influence the duration of single openings. However the mean burst duration decreased for Cao less than 13.5 mM and the rate of bursts declined with a power of almost 2 in low Cao. At Cao less than 1 mM practically no channel openings were observed in presence of glutamate. In order to exclude more rapid desensitization of the glutamate receptors in low Cao as the cause of disappearance of channel openings, glutamate was applied in short pulses with a liquid-filament switch. In 0 Cao also a glutamate pulse did not trigger channel openings. In presence of 13.5mM Cao, the inorganic Ca-channel blockers La3+ and Cd2+ diminished the duration and rate of bursts of channel openings in a similar manner as low Cao. The effects of low Cao and of Cd2+ were tested also on quantal postsynaptic currents, EPSCs, which were recorded through a perfused macro-patch-clamp electrode. At 1.4 mM Cao in the perfused electrode tip, spontaneous EPSCs were reduced at least by a factor of 4, and elicited EPSCs by a factor of 16. Application of Cd2+ had similarly strong effects on the EPSCs. Also the decay of EPSCs was shortened substantially in 1.4 mM Cao or 5 mM Cd2+. The inhibitory Cl(-)-channel of crayfish muscle, activated by glutamate or GABA, also was studied in outside-out patches. The openings of this channel persisted in 0 Cao solutions; the block of channel openings in low Cao thus is a specific property of the excitatory channel. The action of Cao on the excitatory channel may be described as that of a cofactor to glutamate. A possible reaction scheme is proposed.

Animals↗
PubMed1987

Liquid filament switch for ultra-fast exchanges of solutions at excised patches of synaptic membrane of crayfish muscle.

A liquid filament switch is described which can exchange the solution passing an excised outside-out patch of postsynaptic membrane within less than 1 ms. Application and washout of transmitter can be repeated at high rates. Results of such rapid activations by glutamate are shown for the excitatory and the inhibitory channel of crayfish muscle. The excitatory channel is activated within less than 0.5 ms, and after an initial peak of openings desensitizes with a time constant of 5 ms to a low steady-state level. A kinetic scheme of these reactions is proposed. The activation of the inhibitory channel is slower, and this channel desensitizes more slowly than the excitatory one.

Animals↗
PubMed1987

Taste receptors in crayfish: recording of single nicotinamide-activated channels.

The patch clamp technique was adapted to chemoreceptive sensory cells in the claw of Austropotamobius torrentium. In cell-attached and in outside-out patches, concentrations of nicotinamide from 10(-6) mol/liter to 5 X 10(-5) mol/liter activated openings of single channels located in the cell body of the sense cell. The characteristics of these single channel openings were similar to those of neurotransmitter activated channels: the I/V curve was approximately linear, showing a reversal potential of about +15 mV and a conductance of about 33 pS. The mean open time was 1-2 ms. A similar concentration dependence was found for the activation of single channel openings as shown previously for the action potential discharge elicited by nicotinamide at the same preparation.

Action Potentials↗
PubMed1983

Structural properties of bimodal chemo- and mechanosensitive setae on the pereiopod chelae of the crayfish, Austropotamobius torrentium.

The setae on the inner edges of the pereiopod chelae of Austropotamobius torrentium contain eight receptor-cell endings. Two units are mechanosensitive, four react only to amino acids, to amines, or to pyridines. The remaining two units are most probably also chemoreceptors. All sensory cells possess long dendritic outer segments that extend to the tip of the seta, where a small pore is found. Structurally, two units differ from the other six by having (1) densely packed microtubules in their dendritic outer segments, (2) dense A-tubules with arms in their ciliary segments, (3) a well-developed ciliary rootlet in their dendritic inner segments, and (4) desmosomal junctions between the dendritic inner segment and the inner enveloping cell, which contains a scolopale. These features are probably general characteristics of crustacean mechanoreceptors. The mechanoreceptors respond only to strong mechanical stimuli. This corresponds to the structural features of the setae, which lack specialized socket structures. Deflection of the setae may lead to longitudinal stress to the dendrites; the latter seem to be attached proximally to the inner enveloping cell and distally to the cuticle. Thus, the mechanoreceptor structure suggests a function analogous to scolopidial receptors. The chemoreceptors are accessible to chemical stimuli via the subterminal pore. The walls of the setae, however, may be permeable as well. It seems probable that action potentials were recorded also from the dendrites of the sensory cells.

Animals↗
PubMed1980

Single unit analysis of mechano- and chemosensitive neurones in the crayfish claw.

Discharges from single sensory neurones originating in two different hair structures on the chelae of the crayfish Orconectes limosus were recorded. Mechanosensitive units responded to flow alteration or the deflection of single large setae. Chemosensitive units were activated by fish extract in linear dependence on the logarithm of concentration of the chemoexcitant. Mechano- and chemosensitive units differed with regard to the amplitudes of their action potentials and the time distribution of the impulses in a response. Mechanosensitive units were located in the large setae combined in hair clusters, whereas chemosensitive units were found to be situated in the stout setae lining each biting edge.

Action Potentials↗
PubMed1980

Demonstration of three different types of chemosensitive units in the crayfish claw using a computerized evaluation.

The different types of single units, sensitive either to amino acids, amines or 'pyridines' were found in afferent neurones in the claw of Orconectes limosus. The shape of action potentials and the pattern of nerve impulse discharge were characteristic for each type. A computer program used in simultaneous recordings from several units selects up to four units according to spike amplitudes and establishes post-stimulus-time histograms, time interval histograms and average time courses of action potentials for each unit.

Action Potentials↗
PubMed1976

Four types of GABA receptors in crayfish leg muscles characterized by desensitization and specific antagonist.

The effects of application of GABA were studied in the closer and stretcher muscle of crayfish walking legs and compared to those on the opener muscle. EPSPs were measured intracellularly and extracellularly at single synaptic spots, and the input resistance of the muscle fiber was determined. In contrast to the opener muscle, in the closer and stretcher GABA receptors desensitized nearly completely within 5-10 min in the presence of GABA. The presynaptic receptors desensitized more slowly than the postsynaptic ones. While in the opener muscle betaguanidino propionic acid (betaGPA) activates only the presynaptic GABA receptors, in the closer and stretcher muscles both the pre- and the postsynaptic receptors are activated by betaGPA. The postsynaptic GABA receptor on the closer muscle desensitizes in the presence of betaGPA. The results show that with respect to desensitization and the effect of betaGPA four types of GABA receptors can be distinguished. As far as is known from the literature, the homologous synapses in lobster and crab can be assumed to have the same receptor types as those found in crayfish.

Aminobutyrates↗
PubMed1976

Synaptic depression related to presynaptic axon conduction block.

1. The depression of synaptic transmission, which occurs during prolonged repetitive activation, was examined in the opener muscle of the crayfish walking leg. 2. Excitatory post-synaptic potentials (e.p.s.p.s) initially facilitated but then declined to low amplitudes after about 4000 stimulus pulses had been delivered; this depression is presynaptic in origin; 3. Axon conduction blocks occured at points of bifurcation along the entire length of the presynaptic nerve. This resulted in failure of the nerve impulse to invade some branches of the terminal arborization. 4. Nerve terminal invasion failure caused either intermittent or complete inactiviation of some synaptic release sites; this was associated with depression of the post-synaptic response. 5. The statistics of transmitter release during prolonged repetitive stimulation were examined by focal extracellular recording methods. Transmitter release could be described by binomial statistics, and depression involved a drop in m, n and p. 6. The rate of spontaneous quantal release did not decrease, however, arguing against transmitter depletion. 7. It is concluded that repetitive stimulation eventually leads to depolarization of the axon membrane. This causes impulse propagation failure which reduces the number of synaptic release sites that are activated and mimics a drop in the effective stimulation rate; both effects cause synaptic depression.

Action Potentials↗
PubMed1976

Non-uniform probabilities of quantal release at the crayfish neuromuscular junction.

1. Transmitter release at the neuromuscular junction of the crayfish walking leg has been found to deviate from binomial predictions immediately after the onset of repetitive stimulation of the presynaptic nerve at frequencies of at least 15 Hz. 2. After several minutes of continuous stimulation, and at lower rates of stimulation, however, the number of quanta released could be described quite well by binomial or Poisson statistics. 3. Deviations from the theoretical expectations were characterized by (a) fewer release failures than predicted, (b) occasions in which the number of quanta released was more than the estimated number of quanta available for release, and (c) a tendency for the data to be underdispersed. 4. Each of these three characteristics are consistent with the hypothesis that different releasable quanta may have different probabilities of responding to a nerve impulse. 5. Using two different methods, different values of the non-uniform probabilities were estimated from the data. At each synaptic site at least one of the estimated probabilities was very high. 6. The need for caution in interpreting statistical description of quantal release is emphasized.

Animals↗
PubMed1976

Axon conduction block in a region of dense connective tissue in crayfish.

1. The excitor nerve which innervates the opener muscle of the crayfish walking leg was stimulated repetitively for prolonged periods of time. 2. After an initial facilitation and subsequent depression of the postsynaptic potentials, occasional stimulus pulses failed to evoke a postsynaptic response; eventually, every second stimulus pulse failed to produce a postsynaptic potential change. This is termed the 1:1 block state. 3. The block resulted from failure of the appropriate nerve action potentials to propagate through an identifiable region of the axon. This region was in the joint between the propodite and the carpopodite and was characterized by dense surrounding connective tissue. 4. Associated with block development is a decrease in axon conduction velocity and an increase in the amplitude of the postsynaptic potentials; this latter phenomenon is termed anomalous facilitation and results from a decrease in the extent of synaptic depression. 5. The cause of the conduction block resides in the associated nonneural tissue and not in some geometrical property of the axon. 6. It is concluded that extracellular accumulation of K+, because of limited diffusion possibilities and possibly reduced Schwann cell tissue, depolarizes the axon, leading to propagation failure.

Animals↗
PubMedDate not supplied

Molecular cloning of a putative voltage- and cyclic nucleotide-gated ion channel present in the antennae and eyes of Drosophila melanogaster.

The amino acid sequence BCNG-1 (brain cyclic nucleotide gated 1, of the mouse), the first member of mamalian I(h) channels, was used to construct a set of polymerase chain reaction (PCR) primers from possibly conserved regions. Reverse transcription-PCR with Drosophila melanogaster mRNA yielded in a PCR product, which exhibited a high homology to BCNG-1. Using these PCR products to screen a D. melanogaster head cDNA library we isolated a cDNA encoding a member of a new class of putative voltage- and cyclic nucleotide-gated potassium channels from D. melanogaster. The most important features of the amino acid sequence predicted from the cDNA were a C-terminal cyclic nucleotide-binding region, an S4-voltage sensor and a putative potassium-selective pore-forming motif. The high homology of 51% to the sea urchin I(h) channel, which belongs to the same class of ion channels as BCNG-1, leads us to suggest that the Drosophila cDNA is the first insect member of a new class of hyperpolarization-activated and cyclic nucleotide-gated channels. As shown by in situ hybridization, a pronounced mRNA expression was detected in neuronal tissue, including sensory tissue like the compound eyes, and the olfactory and the auditory organs.

Amino Acid Sequence↗
PubMedDate not supplied

Molecular mechanisms of olfactory processing in the mammalian olfactory epithelium.

In humans the sense of smell plays an important role in protecting the organism from external hazards like fire, gas or spoiled food, in the consumption of food and in chemical communication with one another. Increasingly, the study of human olfaction is relevant to a number of medical problems connected with olfactory dysfunction, i.e. neurodegenerative diseases which are also manifested in the olfactory epithelium. Although much is known about behavioral aspects and neuronal activities elicited by odorants, we still cannot clearly describe the molecular mechanisms by which odor stimuli are transformed into an electrical cell signal. Here recent progress in our knowledge about the molecular elements of the transduction machinery are reviewed. It can help to understand the general principles underlying our sense of smell.

Animals↗