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D Dagan

Publications and source records attributed to D Dagan.

At least 37 records · Page 2Linked to original sources
PubMed1992

Properties and rundown of sodium-activated potassium channels in rat olfactory bulb neurons.

We have used single-channel recording techniques to investigate the properties of sodium-activated potassium channels (KNa channels) in cultured rat olfactory bulb neurons, and in large neurons in the mitral cell layer of thin slices of olfactory bulb. Ion channels highly selective for potassium over sodium and chloride, and requiring 10-180 mM internal sodium (Nai) for their activation, were present in approximately 75% of inside-out membrane patches detached from cultured olfactory bulb neurons. Most of these patches contained several KNa channels. KNa channels were seen in cell-attached patches only when Nai was raised by including veratridine in the extracellular medium. Preincubation of the cell in TTX or removal of extracellular sodium prevented this effect of veratridine, confirming that the channels observed under these conditions were indeed KNa channels. Lithium did not substitute for Nai in activating these channels. With 150 mM potassium on both sides of the membrane, KNa channels had a single-channel conductance of 172 pS, and at least two subconducting states were observed in addition to this fully open state. Under these ionic conditions, the channels exhibited linear fully open channel current-voltage curves over the potential range of -100 to 0 mV. At voltages more positive than the potassium equilibrium potential, the single-channel currents exhibited inward rectification as a result of sodium block of outward potassium current. The channels opened in bursts, during which they fluctuated between the fully open and closed states, and the substates. Between bursts they sometimes entered a long-lived inactive state that could last for up to several minutes. In addition, KNa channels in the detached patches exhibited rundown, a progressive irreversible loss in activity, over a time course that varied from less than 1 min to longer than 1 hr. Rundown of KNa channel activity in cell-attached patches (in the presence of veratridine) did not occur, suggesting that some intracellular factor necessary for KNa channel activity is lost when the membrane patch is detached from the cell.

Animals↗
PubMed1990

Alpha interferon suppresses hepatitis B virus enhancer activity and reduces viral gene transcription.

Interferons inhibit replication of hepatitis B virus (HBV). The mechanism for this inhibition was investigated by analyzing the effect of interferons on transcription of a chloramphenicol acetyltransferase reporter gene under control of HBV regulatory sequences and by determining the steady-state level of viral mRNAs in permanently HBV-transfected HepG2 cells. Low doses (100 U/ml) of alpha interferon (IFN-alpha) but not IFN-gamma inhibited chloramphenicol acetyltransferase expression in cultured cells transfected with plasmids containing the HBV enhancer linked to either HBV or simian virus 40 promoters. IFN-alpha also lowered expression of HBV mRNA in HBV-transfected HepG2 cells actively replicating virus, suggesting that IFN-alpha inhibits HBV replication by reducing transcription of viral genes driven by the HBV enhancer.

Chloramphenicol O-Acetyltransferase↗
PubMed1989

Concanavalin A modulates a potassium channel in cultured Aplysia neurons.

A novel 100 pS K(+)-selective ion channel is frequently observed in cell-attached membrane patches from cultured Aplysia neurons. The activity of this channel is moderately voltage-dependent, but channel openings are rare and brief even when the patch is strongly depolarized. However, the activity of the channel is increased dramatically by the addition of the lectin concanavalin A (Con A), to the patch pipette. The channel is also activated by Con A in the bathing medium, suggesting that the lectin's action is via an as yet unidentified intracellular second messenger. In the one single-channel patch studied, Con A had no effect on the channel mean open time; rather it decreased the average duration of the long closed times between bursts of openings. Thus Con A increases either the open probability of single channels, the number of functional channels in the patch, or both. The functional significance of the Con A-induced modulation of K+ channel activity remains to be determined.

Animals↗
PubMed1989

Brush-border membrane cation conducting channels from rat kidney proximal tubules.

This is a description and kinetic characterization of cation channels from rat kidney brush-border membrane vesicles and from apical membranes of proximal tubule cells in culture. Channel activity was demonstrated and characterized in both artificial phospholipid bilayers and in tissue culture. Intermediate conductance, approximately 50 pS, cation-selective channels were observed by both methods. Channels were characterized by a Na permeability (PNa)/K permeability (PK) of 1-5:1. Open-channel current-voltage curves were linear in symmetric 300 mM NaCl. In tissue culture the gating kinetics are described by two open-time constants and two closed-time constants. Channel activity was neither voltage nor Ca2+ dependent and the probability of being in the open state ranged from 0.6 to 0.95. In tissue culture experiments the channel demonstrated nonstationary gating activity. A second, 15-pS cation channel, seen in planar bilayers, demonstrated a higher selectivity for Na+ with a (PNa/PK ratio of greater than 10).

Animals↗
PubMed1987

Inactivating and non-inactivating outward current channels in cell-attached patches of Helix neurons.

Two species of inactivating outward current channels and a non-inactivating voltage-dependent current were seen in cell-attached patches of Helix neurons. Large, slowly inactivating channels had a slope conductance of 44 pS as measured with patch pipets containing the normal extracellular ion concentrations, including 4 mM potassium. Latency to maximal opening was 50-220 ms, and the inactivation time constant averaged 350 ms. Channel opening was decreased by preceding depolarization. The channels were selective for potassium and inhibited by 50 mM TEA. Small, quickly inactivating channels were 14 pS and had kinetics and voltage dependence similar to IA. Patch depolarization also activated a non-inactivating voltage-dependent outward current having channel conductance and/or kinetics such that individual channel openings and closings could not be distinguished. Such current was also seen in the presence of 50 mM TEA, but not in the presence of Co2+, characteristics which are similar to outward hydrogen ion currents, described by others in Helix neurons.

Calcium↗
PubMed1987

Calcium current in growth balls from isolated Helix aspersa neuronal growth cones.

Growth cones were severed from their neurites in primary cultures of Helix aspersa neurons. Following isolation, growth cones rolled up into 5-10-micron-diameter spheres, which remained attached to a poly-L-lysine or lectin-coated glass coverslip. Whole-cell-configuration patch-clamp recordings from isolated growth cones revealed inward calcium currents upon block of outward currents with internally perfused CsCl. Up to 50 microM tetrodotoxin did not affect this current. In 20-micron-diameter spheres, a peak current of 1.2 nA was reached within 3 ms under voltage-clamp conditions for a 60-mV pulse from a holding potential of -50 mV. Channel density calculations averaged to approximately one channel per square micrometer. A two-phase inactivation was evident under voltage-clamp steps from -50 mV to +15 mV. The growth balls described can be internally perfused and voltage clamped to measure ionic currents involved in growth cone function.

Action Potentials↗
PubMed1987

Calcium and barium permeable channels from Aplysia nervous system reconstituted in lipid bilayers.

Ion channels permeable to barium and calcium were reconstituted from the Aplysia nervous system into phospholipid bilayers formed on the tips of patch electrodes. With asymmetrical concentrations of barium or calcium on the two sides of the bilayer, the single-channel currents reversed at the calculated barium or calcium reversal potentials, indicating that the channels were cation selective. Channels with conductances of 10, 25 and 36 pS were routinely observed. Calcium and barium were equally effective as charge carriers for the 36-pS channel, whereas magnesium was at least fifteen-fold less effective. The gating of all three channels was independent of the voltage across the bilayer, but was affected by the dihydropyridine calcium channel agonist Bay K 8644 (Bay K). In the presence of Bay K but not in its absence, long discrete gating events were routinely observed, suggesting that the dihydropyridine increased the probability of long open states as it does for calcium channels in other systems. Bilayers invariably contained more than a single channel (or conductance state). This was observed even when the Aplysia nervous system membranes were prepared in the presence of cytoskeleton disrupting agents, or when the membrane proteins were diluted extensively with exogenous phospholipid. Furthermore, transitions between conductance levels were observed with high frequency. These findings, together with the fact that all of the conductance states share certain properties including voltage-independence and sensitivity to Bay K, suggest that the apparent multiple channel types may in fact represent subconductance states of a single ion channel.

Animals↗
PubMed1984

Chemical and electrotonic connections between Aplysia neurons in primary culture.

Dissociated Aplysia neurons will regenerate neurites and form functional connections in primary cell cultures. The specificity of intercellular connectivity in these cultures was investigated by coculturing neurosecretory bag cells with neurons dissociated from the buccal ganglion. It was found that bag-bag and buccal-buccal electrotonic synapses form with high frequency, consistent with previous findings in pure bag and buccal cultures. There is specificity in the formation of these connections, since no bag-buccal electrotonic synapses were observed. Chemical interactions, on the other hand, are present between bag and buccal neurons. In a buccal-bag pair, injection of sufficient depolarizing current into the buccal cell to elicit a train of action potentials leads to a slow hyperpolarizing response in the bag cell. The bag cell hyperpolarization is accompanied by an increase in the cell's input conductance. This connection appears to be unidirectional, produces a voltage shift in the bag cell which is opposite in sign to that in the buccal cell, and is blocked by the removal of Ca2+ from the extracellular medium, indicating that it is mediated by a chemical neurotransmitter. The selective formation of electrotonic synapses in these mixed bag-buccal cultures, together with the presence of chemically mediated interactions, make this system particularly useful for investigating the establishment of intercellular connectivity.

Animals↗
PubMed1981

Transient and long-term effects of temperature on electrogenic activity of Drosophila nerves and muscles.

Electrical responses of indirect flight muscles in Drosophila fruit flies are markedly affected by a 10 degree C increment from ambient temperature: refractory period of evoked neuromuscular responses is shortened with temperature elevation due to effects on neuronal components. Excitation threshold of these muscle fibers increases transiently during elevation of temperature, while the frequency of directly-evoked muscle spikes increases gradually. These temperature-induced changes are reversible upon lowering the temperature back to ambient temperature.

Animals↗
PubMed1981

Triplicated bursting neuron R15 in an Aplysia abdominal ganglion: non-symmetrical coupling, common synaptic inputs and response to dopamine.

An abdominal ganglion of the mollusc Aplysia californica was found to contain 3 neurons in the place normally occupied by a single R15 cell. The 3 neurons exhibited properties characteristic of R15 neurons including spontaneous bursts. The bursts appeared asynchronously in spite of electrotonic coupling between them. The coupling function approximated a low pass filter with a cut-off frequency between 0.02 and 0.05 Hz in accordance with a measured coupling time-constant of 5--10 sec. Coupling measured in the cell body was found to be stronger for hyperpolarizing currents than for depolarizing currents injected into any of the 3 cells. This 'symmetrical rectification' can be explained by a rectifying axonal membrane interposed between the site of coupling and the site of recording. All 3 cells were found to have dopamine receptors and to receive common synaptic inputs. Since the coupling efficiency was found to vary depending on the direction of current flow, depolarizing synaptic inputs and spike burst generation remain autonomous.

Animals↗
PubMed1981

Isolated identified Aplysia neurons in cell culture.

Methods have been developed for primary culture of large identified Aplysia neurons. Aplysia ganglia were treated with neutral protease to soften the connective tissue sheath. Individual neurons were isolated either by manipulation with tungsten needles or by tying off their axons with fine nylon filament and were immobilized in a chick plasma clot or a solution of methylcellulose. Somata up to approximately 300 micrometers in diameter extended long processes within several hours in culture. A single neuron produced as many as 10 processes which could grow at different rates. Intracellular recordings showed spontaneous and evoked action potentials in neurons cultured for up to 6 weeks. Electrical synapses formed between pairs of neurons in culture. In several culture dishes containing neurons from buccal ganglia, electrical coupling was observed between 90% of the cell pairs tested. This primary culture system currently is being used to compare the electrical and biochemical properties of neuronal processes with those of cell bodies and to study the conditions necessary for process regeneration and synapse formation between isolated identified neurons.

Animals↗
PubMed1977

New technique for movement analysis: application to biological systems.

A new system for motion analysis is described. Modulation of light intensity of an organism's movement over an opaque and transparent checkerboard grid is monitored by a photocell. The photocell's output is proportional to the organism's amplitude and frequency of movement. This output is analyzed by a continuous interval dot display and spectrum analysis. The system was tested by analyzing the activity of 4 Drosophila strains which are known to differ in their activity. General applicability of the system is discussed.

Animals↗