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H Hatt

Publications and source records attributed to H Hatt.

At least 55 records · Page 3Linked to original sources
PubMed1995

Dopamine enhances glutamate-activated currents in spinal motoneurons.

In cultured embryonic chick motoneurons, glutamate-activated currents rise quickly and then decay rapidly to relatively small steady-state current levels. Dopaminergic modulation of these receptors was studied using patch-clamp recording techniques. At concentrations > or = 10 nM, dopamine enhanced glutamate-activated currents by about 200%. This enhancement was diminished by the nonspecific dopamine receptor antagonist S(+)-apomorphine and the more specific D1 receptor antagonist SCH23390, and it was mimicked by the D1 partial agonist SKF38393. Glutamate receptor desensitization rate was not altered in the presence of dopamine. Enhancement was specific to the kainate component. Current-variance analysis indicated that in the presence of dopamine the conductances of glutamate-activated channels were not altered but that the relative fraction of kainate-type channels activated by glutamate increased. Intracellular cAMP levels increased by 33% following exposure to 100 microM dopamine. The effects of elevated cAMP or protein kinase A (PKA) were tested by including 100 microM cAMP or PKA, respectively, in the recording pipette solution. This increased the kainate-activated currents specifically. Dopaminergic enhancement was not observed when a PKA inhibitor was in the pipette. mRNA encoding D1 was detected in the spinal cord by a reverse transcription, polymerase chain-reaction amplification procedure. Thus, dopamine is acting most probably on an avian homolog of the D1 receptor family. We conclude that dopamine causes cAMP to increase, which results in increased activation of kainate-gated channels during glutamate-mediated transmission.

Animals↗
PubMed1995

Dopaminergic modulation of glutamate-activated channels in the central nervous system.

Modulation of glutamate-activated currents by dopamine was studied in identified central neurons, alpha-motoneurons of the chick and horizontal cells of the perch. This modulation is mediated by a cAMP-dependent protein phosphorylation. The activation and desensitization time constants of glutamate currents were determined before and after incubation with dopamine. In the horizontal cells ultrafast glutamate (AMPA or quisqualate) application prior to the the dopamine incubation gives rise to fast transient current responses which desensitize within less than 100 ms. Kainate produced higher steady state currents. After incubation of the cells with dopamine (100 nM) for 30s the desensitization was dramatically reduced, but the amplitudes of the steady state currents were similar to the transient control currents. Kainate activated currents were not affected. In alpha-motoneurons the exposure to dopamine (100 nM) for 1 min was sufficient to increase the peak and steady state amplitudes but not the desensitization time constant of glutamate activated currents. Here enhancement was specific to the kainate component of glutamate activated currents; the decreased variance of currents reflects increased kainate channel activation. Measurements of motoneuronal cAMP concentrations showed an increase following addition of dopamine. mRNA encoding both D1 and D2 dopamine receptor subtypes was detected. We conclude that the dopamine dependent modulation which is mediated by a protein phosphorylation is due to an alteration of the desensitization of AMPA type receptors in horizontal cells and of the activation of kainate type receptors in motoneurons.

Animals↗
PubMed1994

Dopamine alters glutamate receptor desensitization in retinal horizontal cells of the perch (Perca fluviatilis).

The patch-clamp technique in combination with a fast liquid filament application system was used to study the effect of dopamine on the glutamate receptor desensitization in horizontal cells of the perch (Perca fluviatilis). Kinetics of ligand-gated ion channels in fish horizontal cells are modulated by dopamine. This modulation is presumably mediated by a cAMP-dependent protein phosphorylation. Before incubation with dopamine, the glutamate receptors of horizontal cells activate and desensitize with fast time constants. In the whole-cell recording mode, fast application of the agonists L-glutamate, quisqualate, or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid prior to the dopamine incubation gives rise to fast transient currents with peak values of about 200 pA that desensitize within 100 ms. Kainate as agonist produced higher steady-state currents but no transient currents. After incubation of the cells with dopamine for 3 min, the desensitization was significantly reduced and the agonists L-glutamate, quisqualate, or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid induced steady-state currents with amplitudes that were similar to the previously observed transient currents. Kainate-induced currents were only slightly affected. Fast desensitizing currents upon fast application of L-glutamate were also recorded from outside-out patches that were excised from horizontal cells before incubation with dopamine. The currents from excised patches desensitized to a steady-state level of about 0.2 of the peak amplitude with time constants of less than 2 ms. When the outside-out patches were excised from cells after dopamine incubation, steady-state currents were enhanced and no transient currents were observed. The results may indicate that the dopamine-dependent modulation of glutamate-induced currents, which is presumably mediated by a protein phosphorylation, is due to an alteration of the desensitization of the glutamate receptors.

Animals↗
PubMed1994

Cyclic nucleotide- and inositol phosphate-gated ion channels in lobster olfactory receptor neurons.

The idea of having two second messenger pathways in olfaction, one mediated by cAMP and the other by inositol 1,4,5-trisphosphate, is supported by evidence that both second messengers directly activate distinct ion channels in the outer dendrite of lobster olfactory receptor neurons. Evidence that both types of second messenger-gated channels can occur in the same patch of membrane suggests that channels of both types can be expressed in one neuron. Evidence of more than one type of inositol phosphate-gated channel in this highly specialized region of the neuron furthers the idea that the output of individual olfactory receptor cells is regulated through multiple effectors and allows that effector diversity may contribute to functional diversity among olfactory receptor cells.

Animals↗
PubMed1994

Cloning and functional expression of a cyclic-nucleotide-gated channel from mammalian sperm.

Cyclic nucleotide-gated (CNG) channels serve as downstream targets of signalling pathways in vertebrate photoreceptor cells and olfactory sensory neurons (see ref. 1 for review). Ca2+ ions that enter through CNG channels intimately control these signalling pathways by regulating synthesis or hydrolysis of cyclic nucleotides, and by decreasing ligand sensitivity of CNG channels. Several lines of evidence suggest that cyclic nucleotides and Ca2+ play important roles in chemotaxis of invertebrate sperm and fertilization (see ref. 9 for review), whereas their mechanisms of action in vertebrate sperm are largely unknown. Here we report the cloning and functional expression of a novel CNG channel from bovine testis. The channel polypeptide was functionally localized in sperm, but is also specifically expressed in cone photoreceptor cells. These channels might be involved in chemotaxis of sperm by controlling Ca2+ entry through a cyclic-nucleotide signalling pathway.

Amino Acid Sequence↗
PubMed1994

Patch-clamp study of membrane properties and GABA-activated currents of rat magnocellular supraoptic neurons in thin slice preparation.

The magnocellular neurons of the rat supraoptic nucleus were investigated by using (a) the patch-clamp technique on thin brain slice preparations to demonstrate voltage- and GABA-activated ionic currents, and (b) immunohistochemistry to demonstrate the expression of the beta 2 and beta 3 subunits of the GABAA-receptor on their membrane surface and the contents of the neuropeptides vasopressin and oxytocin. During electrophysiological recording in the whole-cell mode neurons were stained with Lucifer Yellow and camera lucida drawings were made. Two types of neurons could be distinguished by their different K(+)-currents, an inactivating and a noninactivating type. All neurons had a fast Na+ inward current. GABAA-activated currents were characterized by investigation of their ionic conductance and by blocking experiments with the GABAA-antagonist bicuculline.

Animals↗
PubMed1993

Electrophysiological and morphological properties of granule cells: patch-clamp recordings of newborn rabbit olfactory bulb slices.

Granule cells were investigated by performing whole-cell patch-clamp recordings from thin slices of the olfactory bulb of newborn rabbits. Granule cells were intracellularly stained with Lucifer Yellow in their intact environment. During current-clamp measurements these neurones were characterized by their lack of action potentials upon depolarization. Evidence for a Ca2+ dependent K+ conductance was found. Two types of outward currents were identified in the whole cell mode during voltage clamp; a non-inactivating K+ current that shared some properties of the delayed rectifier K+ current and a non-inactivating K+ current were recorded. No fast inward current was registrated.

Action Potentials↗
PubMed1993

Rapid application and removal of second messengers to cyclic nucleotide-gated channels from olfactory epithelium.

The last step in the second-messenger cascade mediating vertebrate olfactory transduction is the direct opening of a nonspecific cation channel by cAMP. The kinetic properties of this interaction are critical in determining the time course of the sensory response. To analyze these properties, excised inside-out membrane patches containing either the native channel from salamander olfactory-receptor neurons or a recombinant rat olfactory cyclic nucleotide-gated channel were exposed to short pulses of known concentrations of cAMP or cGMP to mimic a rapid and transient production of second messenger. Channel activity outlasted cyclic nucleotide pulses for several hundred milliseconds. This effect was due to an intrinsic property of the olfactory channel protein because it did not occur with cGMP-activated channels from retinal photoreceptors. Gating kinetics of the olfactory channel were both voltage and agonist dependent. These results demonstrate that the overall slow channel-gating kinetics could account for the difference in time course between the odor-induced changes in cAMP concentration and the subsequent sensory generator current.

Ambystoma↗
PubMed1992

Recovery from the rapid desensitization of nicotinic acetylcholine receptor channels on mouse muscle.

Pulses of acetylcholine (ACh) applied to outside-out patches of embryonic-like muscle membrane elicited channel currents which declined rapidly (tau d = 10-60 ms) due to desensitization. Recovery from desensitization was determined by pulse pairs, varying the pulse interval. When the pulse interval was about 300 ms, the response to the second pulse was about half that to the first pulse, i.e. about half of the channels had recovered from desensitization. The results are discussed in the frame of a cyclic reaction scheme. If this scheme includes high affinity binding of ACh to desensitized receptors, it can also explain the finding that low ACh concentrations (less than or equal to 1 microM) largely desensitize the receptors, but elicit very little channel opening.

Acetylcholine↗
PubMed1992

Patch-clamp recordings of spiking and nonspiking interneurons from rabbit olfactory bulb slices: membrane properties and ionic currents.

Physiological and morphological properties of rabbit, Oryctolagus cuniculus, olfactory bulb interneurons were characterized by using a thin slice preparation in combination with patch-clamp measurements and Lucifer Yellow fills. Two types of interneurons, periglomerular (PG) and juxtaglomerular (JG) cells, were unequivocally distinguished in the glomerular layer. Their properties were compared to those of mitral cells. PG cells closely resembled previously described periglomerular cells in their morphology. During current clamp recording these neurons were characterized by their lack of action potentials upon depolarization. Consistent with these results no Na+ currents could be elicited in voltage clamp experiments. Two types of outward K+ currents were distinguished: one which inactivated and one which did not. From their morphology JG cells appear to be either short axon cells or external tufted cells. JG cells always responded with a single, TTX-blockable action potential in response to maintained current injection. Two types of membrane currents were identified in JG cells during voltage clamp: a fast, inactivating Na+ current that was fully activated at -80 mV, and a sustained outward current that shared some properties with a delayed rectifier K+ current. The particular relationship between the voltage dependence of the Na+ and K+ currents appeared to preclude repetitive spike activity.

Action Potentials↗
PubMed1992

Patch-clamp recordings of spiking and nonspiking interneurons from rabbit olfactory bulb slices: GABA- and other transmitter receptors.

Transmitter receptor ion channels from previously identified rabbit olfactory bulb neurons were studied by using a thin slice preparation in combination with patch-clamp measurements. PG cells, which closely resembled previously described periglomerular interneurons in their morphology, responded to microapplication of GABA, acetylcholine, norepinephrine and glycine with the activation of distinct ionic currents. JG cells, which belong either to the class of short axon cells or external tufted cells, never showed GABA responses. In mitral cells ionic currents activated by GABA, acetylcholine, norepinephrine and glutamate could be elicited. Further measurements of GABA-activated currents of PG cells were made and indicated that these cells expressed two different types of GABA receptors: one which showed fast desensitization with a decay time constant of about 5 s, and one which slowly desensitized with a decay time constant of about 20-30 s. Both types were completely inhibited by bicuculline methiodide (50 microM). GABA receptors were not blocked by Zn2+ (0.1 mM). From the dose-response relationship of the peak GABA-activated currents, an apparent dissociation constant of 50 microM was derived. From single channel measurements in excised outside-out patches, a single channel conductance of GABA-activated Cl- currents of 24 pS was obtained during continuous application of the agonist. Single channel events had a mean open time of 1.9 ms.

Animals↗
PubMed1992

Activation and desensitization of embryonic-like receptor channels in mouse muscle by acetylcholine concentration steps.

1. Pulses of acetylcholine (ACh) in concentrations between 0.1 and 1000 microM were applied repetitively to outside-out patches of enzymatically denervated (14 days) mouse muscle with the liquid filament switch. Solutions superfusing the patch could be changed rapidly (within 0.2 ms). 2. Single-channel activity was studied under steady-state conditions in the outside-out and in the cell-attached mode. The single-channel conductance was 26 pS in outside-out patches, characteristic for embryonic-like channels. Apparent mean open time was about 2.5 ms, a shorter component of closed times was 800 microseconds and burst length was about 5 ms. 3. Channel currents elicited by pulses of ACh were averaged. The time-to-peak current was concentration dependent and decreased from a level of about 10 ms below 10 microM to about 400 microseconds at 100 microM-ACh. 4. For a typical experiment, the average peak current, imax, increased from -0.4 pA with 0.1 microM to -82 pA with 1000 microM-ACh, close to the value at saturation. The half-maximal response was at 60 microM-ACh. The dose-response curves for imax had double-logarithmic slopes of 1.1-1.3, consistent with two binding sites at the embryonic nicotinic acetylcholine receptor (nAChR). 5. The current elicited by ACh pulses decreased rapidly after the peak. The time constant of desensitization increased from 20-50 ms with 1000 microM-ACh to up to more than a second with 1 microM-ACh. 6. The current in steady state (fully desensitized) increased up to 10 microM-ACh, but decreased slightly to values of imax/100 to imax/500 when higher concentrations were applied. 7. In addition to the well-known differences between adult and embryonic nAChR concerning the apparent mean open time and burst length, we found differences in the slope of the dose-response curve for imax, in the ratio of peak to steady-state response, and in the rise time of the response.

Acetylcholine↗
PubMed1992

Olfactory receptor neurons from antennae of developing male Manduca sexta respond to components of the species-specific sex pheromone in vitro.

Male-specific olfactory receptor neurons, dissociated from developing antennae of the moth Manduca sexta and grown in long-term primary cell culture, can respond to at least one component of the female moth's sex-pheromone blend with the opening of a nonspecific cation channel. This response does not require the coapplication of pheromone-binding protein.

4-Aminopyridine↗
PubMed1991

Dual activation of a sex pheromone-dependent ion channel from insect olfactory dendrites by protein kinase C activators and cyclic GMP.

Olfactory transduction is thought to take place in the outer dendritic membrane of insect olfactory receptor neurons. Here we show that the outer dendritic plasma membrane of silkmoth olfactory receptor neurons seems to be exclusively equipped with a specific ion channel activated by low concentrations of the species-specific sex pheromone component. This so-called AC1 channel has a conductance of 56 pS and is nonselectively permeable to cations. The AC1 channel can be activated from the intracellular side by protein kinase C activators such as diacylglycerol and phorbolester and by cGMP but not by Ca2+, inositol 1,4,5-triphosphate, or cAMP. Our results imply that phosphorylation of this ion channel by protein kinase C could be the crucial step in channel opening by sex pheromones.

Adenosine Triphosphate↗
PubMed1991

Altered Na+ channel activity and reduced Cl- conductance cause hyperexcitability in recessive generalized myotonia (Becker).

Intact muscle fibers or resealed fiber segments from 7 patients with recessive generalized myotonia were studied in vitro. All fibers had normal resting membrane potentials and normal resting [Ca2+]i several hours after removal. Contractions were characterized by slowed relaxation which was due to electrical after-activity. Often spontaneous depolarizations were recorded intracellularly. In all fibers, the steady state voltage-current relationship was abnormal, due to a reduced Cl- conductance. However, this conductance ranged from 0% to 66% of the total membrane conductance, whereas, in normal muscle, it was 80%. Theoretically, myotonic after-discharges would not appear until the Cl- conductance is below 20%. Thus, the membrane hyperexcitability must be due to another defect, at least in the preparations in which the Cl- conductance was only slightly reduced. In all patches from all patients investigated with the patch clamp technique, we observed reopenings of the Na+ channels throughout depolarizing pulses (such behavior was absent in normal muscle). If a patch was polarized to potentials less negative than the resting potential, the duration of the reopenings increased. We conclude that a combination of reduced Cl- conductance and the reopenings of Na+ channels underlie the electrical after-activity in recessive generalized myotonia.

Chlorides↗