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J Dudel

Publications and source records attributed to J Dudel.

At least 73 records · Page 4Linked to original sources
PubMed1989

Long-term survival of decentralized axons and incorporation of satellite cells in motor neurons of rock lobsters.

Previous electrophysiological experiments have shown that in the abdominal extensor muscles of rock lobsters, axons which were cut in surviving animals do not degenerate peripherally for several months, but conduct action potentials and release transmitter quanta on stimulation closely distal to the scar. Electron micrographs from the axon distal to the scar (in a reliably conducting region) show invasion of the axoplasmic space by nucleated cells, probably glia. After several months, the cell membranes of the invaders have vanished and apparently functional multiple nuclei remain. We suggest that decentralized axons may survive for months with the help of 'donated' nuclei.

Action Potentials↗
PubMed1989

Chloride channels gated by extrajunctional glutamate receptors (H-receptors) on locust leg muscle.

Outside-out patches of extrasynaptic membrane were isolated from leg muscles of locusts. L-Glutamate and its agonists were applied to such patches either continuously or in rapidly switched pulses. When the pipette contained a high chloride concentration, 2.5 x 10(-5) M glutamate triggered single-channel currents (gated by H-receptors) with a conductance of 25 pS which were carried by chloride, in addition to cationic channels (gated by D-receptors). For the chloride channels, the distribution of channel open times had components of about 2 and 12 ms. Pulses of higher glutamate concentrations elicited many superimposed channel openings, and the approximately saturating concentration of 10(-3) M glutamate opened 100-200 channels simultaneously. When the pipette contained low chloride, channel conductance was reduced, and the current voltage relation was shifted towards the now negative chloride equilibrium potential. H-Receptor-gated chloride channels were activated by glutamate, ibotenate and aspartate, but not by GABA, quisqualate, kainate, N-methyl-D-aspartate and carbachol. The currents declined in the continued presence of agonist showing a time constant of desensitization greater than 1 s. Recovery from desensitization after removal of the agonist was tested with double pulses and was found to have a time constant of about 300 ms.

Animals↗
PubMed1989

Calcium dependence of quantal release triggered by graded depolarization pulses to nerve terminals on crayfish and frog muscle.

Quantal transmitter release was measured in small portions of neuromuscular junctions by means of a perfused macro-patch-clamp electrode. Release was elicited by graded current pulses through the recording electrode (excitation blocked by TTX). On increasing the stimulation current from a threshold amplitude, release rose steeply for several orders of magnitude and finally approached a saturation level of about 10 quanta/pulse. Reduction of the Ca concentration in the perfusate of the electrode, Cae, depressed the saturation level of release relatively little and had practically no effect on the threshold current amplitude, as long as the Ca concentration in the superfusion of the bath, Cab, remained high. When Cab was reduced too, the depression of release was more severe. The dependence of release on Cae was determined for a large range of Cae for saturating depolarization pulses. In crayfish, at 0 Cab, in double-logarithmic release-Cae plots the maximum slope was on average 3.9, and this slope dropped to on average 2.1 in 13.5 mM Cab. In frog, at 0 Cab, the respective double-logarithmic slope was 3.5, while in 1.8 mM Cab this slope declined dramatically, the rate of release decreasing on average only by a factor of 3.8 from 10 mM to 0.02 mM Cae. These results are interpreted by the assumption that the resting Ca concentration in the terminal, Cair, has strong influence on the rate of release due to depolarization pulses in low Cae, and that Cab has control on Cair in the terminal.

Animals↗
PubMed1989

Shifts in the voltage dependence of synaptic release due to changes in the extracellular calcium concentration at nerve terminals on muscle of crayfish and frogs.

The rate of release of transmitter quanta, elicited by variable depolarization pulses applied to a nerve terminal by means of a macro-patch-clamp electrode, was measured in muscles of crayfish and frogs. The electrode was perfused with solutions containing different Ca concentrations, Cae. The bath was superfused separately, usually with solutions containing nominally no Cab and elevated Mgb. A fixed depolarization pulse followed the variable test pulse within 7-10 ms, and facilitation, Fc, of release after the fixed pulse was determined as a measure of Ca-inflow during the test pulse. As described before, Fc always showed a peak, Fc, at depolarization amplitudes of the test pulse below the saturation level of release. When Cae was changed, the depolarization levels generating Fc shifted in a negative direction if Cae was lowered, and in a positive direction if Cae was increased. These shifts agreed with the known dependence of the effective membrane potential (controlling e.g. Ca inward current) on Cae which is due to shielding of surface changes by Ca2+ (cf. Hille 1984). Changes of Cab, at constant Cae, did not affect the depolarization dependence of Fc. It is concluded that Ca inflow is not the only factor controlling quantal release, and that at least in depolarizations beyond those eliciting Fc another potential dependent factor increases release while Ca inflow presumably falls.

Animals↗
PubMed1989

Calcium and depolarization dependence of twin-pulse facilitation of synaptic release at nerve terminals of crayfish and frog muscle.

Transmitter quanta were elicited from nerve terminals of crayfish and frog muscle by depolarization pulses through a macro-patch-clamp electrode. The rates of quantal release for twin pulses and their ratio, twin pulse facilitation, Fd, were determined. When the electrode was perfused with normal Cae (13.5 mM for crayfish, 1.8 mM for frog), Fd was low for threshold depolarizations, increased to a maximum at medium depolarizations, decreased when the rate of release due to the first pulse approached saturation, and increased again for larger depolarizations. If under these conditions the superfusion of the muscle outside the electrode was changed from normal to 0 Cab and high Mgb solution, Fd increased. When the Ca concentration around the terminal, Cae, was reduced to levels at which release did not reach the saturation level for large depolarizations, Fd in dependence on depolarization did not show the minimum at higher depolarizations. The amplitude of Fd measured for large, constant depolarization pulses showed a maximum at a Cae below that of the normal solution. The maximum of Fd was much higher if the superfusion of the bath contained 0 Cab and high Mgb than when normal bathing solution was superfused. The maxima of Fd at a low value of Ca inflow are predicted by the "residual Ca" theory of facilitation, if release is influenced by a resting low internal Ca concentration, Cair, and reaches a saturation level for large Ca-inflow. It is also predicted that decreasing Cair (as in low Cab) will increase Fd.

Animals↗
PubMed1989

Twin pulse facilitation in dependence on pulse duration and calcium concentration at motor nerve terminals of crayfish and frogs.

Phasic release from motor-nerve terminals of crayfish and frogs was elicited and recorded by means of a macro-patch-clamp electrode through which the terminal was depolarized in graded pulses. The tip of the electrode was perfused and the Ca concentration around the terminal, Cae, was controlled independent from that in the superfusion of the muscle, Cab. Release increased with pulse duration with a double-logarithmic slope of 5 to 9 in crayfish and frogs, which represents a form of "early facilitation" (Katz and Miledi 1968). In crayfish, this relation was shifted to longer pulse durations on lowering Cae, while in frogs, in addition, the saturation level of release was suppressed at low Cae. Responses to twin pulses with intervals of 7-10 ms showed facilitation, Fd. When pulse duration of the twin pulses was increased, starting from about 0.5 ms, Fd increased to a maximum, but declined for longer pulses which elicited release approaching the saturation range. On lowering Cae, the maximum of Fd, Fd, increased in amplitude and was shifted to larger pulse durations. Also reduction of Cab increased Fd. The effects of pulse duration and of Cae and Cab on Fd are predicted by the residual Ca theory of facilitation, if it is assumed that changes of Cae produce corresponding changes in Ca inflow during depolarization, and if the resting intracellular Ca concentration is influenced by the extracellular Ca concentration. The large values of early facilitation can not be explained by the residual Ca theory of facilitation and may indicate the action of another depolarization dependent factor which joins in the control of release.

Animals↗
PubMed1989

Argiopine blocks glutamate-activated single-channel currents on crayfish muscle by two mechanisms.

1. The effect of the spider venom argiopine on L-glutamate-activated membrane channels of crayfish muscle was investigated using the patch-clamp technique. 2. When 10(-2) M-glutamate and 10(-9) M-argiopine were contained in the pipette solution of a cell-attached patch, bursts of openings of excitatory channels appeared after formation of the patch. These bursts ceased abruptly after variable periods of time in the range of 5 min. Higher concentrations of argiopine (up to 10(-6) M) blocked more rapidly, approximately in proportion to concentration. 3. The block of excitatory channels could be partially or completely reversed by hyperpolarizing the membrane by up to -190 mV from the resting potential. The time constant of the recovery of channel opening decreased with increasing hyperpolarization and was 2 ms with -160 mV hyperpolarization. Switching back from the hyperpolarized level to the resting potential, the time constant for the resulting block was about 3 s (10(-7) M-argiopine). Potential-dependent block by argiopine with similar characteristics was also observed in outside-out patches. 4. Up to argiopine concentrations of 10(-7) M the kinetics of channel openings and of bursts measured in pre-block periods or during reversal of the block by hyperpolarization were indistinguishable from controls. 5. When the potential-dependent block observed in the presence of 10(-6) M-argiopine and 10(-2) M-glutamate was reversed by hyperpolarization, additional short closings occurred during bursts. This 'flickering block' did not change burst length appreciably, but an additional open time component (tau = 0.1 ms) appeared and the average open time per burst was reduced. 6. At least two reaction steps seem necessary to model the behaviour of the potential-dependent block. The flickering block may be described as intermittent blocking of the channel which does not interfere with the reactions between glutamate and the channel.

Animals↗
PubMed1988

Rapid activation and desensitization by glutamate of excitatory, cation-selective channels in locust muscle.

Outside-out patches of membrane were excised from extensor tibiae muscles of locusts. L-Glutamate or its agonists were applied to such patches in short pulses by means of a lipid filament switch. Cationselective, excitatory channels were activated by quisqualate, L-glutamate and aspartate (in decreasing order of effectivity), but not by ibotenate, kainate, N-methyl-D-aspartate and glycine. At high agonist concentrations, channel activation reached a peak within 1 ms. Two kinetic types of channels have been identified: L-channels with on average relatively long and S-channels with short openings. Both types of channel openings showed surprisingly high rates of desensitization, channel activity declining after the initial surge to zero with time constants of about 25 and 3 ms, respectively. The L-channels exhibit open times close to those of channels recorded in M omega-seal studies. The S-channel has not been reported previously.

Animals↗
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

Single glutamate-gated synaptic channels at the crayfish neuromuscular junction. I. The effect of enzyme treatment.

Single glutamate activated ionic channels were recorded with the patch clamp technique from untreated crayfish muscle fibres with M omega seals, and after treatment with collagenase, with G omega seals. In regions with single channel activity spontaneous synaptic currents could also be recorded, and the channels were therefore identified as synaptic. The single channel current amplitude was -7 to -8 pA at the resting potential of -70 mV, representing a conductance of 100 pS. The amplitudes decreased by a factor of two when the temperature was lowered by 10 degrees C. Openings occurred in bursts, and the mean burst length varied between 0.3 ms (50 microM glutamate in the pipette) and 0.8 ms (1 mM glutamate in the pipette). After treatment with collagenase, G omega seals could be formed. The conductance of the channel and the mean burst length was not affected by the enzyme, but after treatment active spots could be found easier and they were distributed more uniformly along the fibre. After treatment the concentrations of glutamate necessary to elicit channel openings were higher (100 microM compared to 20-50 microM) and simultaneous openings of two or more channels were observed very rarely. Synaptic currents could not be recorded from preparations cleaned by collagenase (2 mg/ml) for longer than 60 min.

Animals↗
PubMed1987

Single glutamate-gated synaptic channels at the crayfish neuromuscular junction. II. Dependence of channel open time on glutamate concentration.

Single, glutamate activated ionic channel currents were recorded from crayfish muscle in the cell attached mode. Different concentrations of glutamate were present in the patch clamp pipette. Bursts of openings were observed with a concentration dependent number of short gaps per burst. Also the mean burst length was concentration dependent and varied between 0.3 ms (100 microM) and 1.3 ms (20 mM). Even with the highest concentrations of glutamate the channel activations were well separated and the beginning and the end of a burst could be defined. The distributions of open times and of burst lengths could be fitted well with a single exponential component for all studied concentrations of glutamate. The distributions of closed times were composed of two or three exponential components (with possibly more than one channel contributing). The mean burst length was compared with the time constants of decay of synaptic currents (0.8-3.0 ms at 19 degrees C) which were measured either with the same pipette as the single channel currents or with a macro patch technique. An estimation of the glutamate concentration at the receptors during synaptic transmission gave values in the millimolar range. The most simple model of glutamate-receptor interaction contains two binding sites for glutamate but no singly liganded open states. Rate constants were estimated for this model.

Animals↗
PubMed1987

Augmented synaptic release by one excitatory axon in regions in which a synergistic axon was removed in lobster muscle.

1. In the lobster, every fibre of the lateral abdominal extensor muscle is innervated by two excitatory axons. When one of the excitatory axons (the common excitor) was removed chronically by intracellular injection of pronase, terminals of the remaining axon (the specific L1 excitor) showed augmented transmitter release. 2. Evidence as to the mechanism of this strengthening can be obtained taking advantage of the peculiar innervation pattern of the abdominal extensors. The L1 excitor axon of one segment sends a branch to part of the next posterior segment. The common excitor axon innervates only muscle fibres of its own segment. 3. 10-20 days after removing the common excitor axon of segment II, the quantum content of release of terminals of the L1 excitor axon was measured in segments I, II and III. Terminals of the L1 excitor axon of segment I which innervate segment II released much more transmitter than controls, while the terminals of the same axon innervating segment I remained normal. Similarly, terminals of the L1 excitor axon of segment II became 'stronger' in segment II but remained normal in segment III. 4. It is concluded that only those terminals of one axon which innervate targets with reduced innervation increased the average release rate. It seems that the signal for synaptic strengthening, after removal of a synergistic axon, is generated and acts locally in partially denervated muscle fibres.

Action Potentials↗
PubMed1986

Transmitter release from nerve terminals evoked by depolarization pulses contains a short phase of repression.

The time course of quantal transmitter release after a depolarization pulse was measured at frog and crayfish motor nerve terminals. Test pulses were arranged to elicit low release, and the delay of first releases and the median of distributions of release times were defined for large (greater than 2000 stimuli) samples. Small, subthreshold depolarizing post-pulses were added directly after the test pulses. Such post-pulses of 1 to 4 ms duration prolonged the delay of first releases and shifted the median of the time course of release by up to 3 ms (at 0 degree C) depending on the duration and on the amplitude of the post-pulses. These 'latency shifts', which have been observed after prolonged depolarizations by other authors, were statistically highly significant. The results of post-pulses were very similar at neuromuscular junctions of frog and crayfish. It is concluded that depolarization in addition to the promotion of release has a short repressing action on release which is partly responsible for synaptic delay.

Animals↗
PubMed1986

Dependence of double-pulse facilitation on amplitude and duration of the depolarization pulses at frog's motor nerve terminals.

Motor nerve terminals of the frog were depolarized by pairs of pulses with 5 to 10 ms interval and the resulting quantal transmitter releases were determined. In 'fixed pulse facilitation', Fc, the second pulse was kept constant, and the effect of a varying pre-pulse was measured, comparing the thus facilitated release after the fixed pulse to control release after the fixed pulse alone. If depolarization in the pre-pulse was increased from threshold to almost saturation level of release, Fc had a maximum, Fc, at about 1/10 the saturation level of release, as reported before. In 'double-pulse facilitation', Fd, two identical pulses were applied, and the facilitated release after the second pulse was compared to control release after the first pulse. On increasing pulse duration from 0.4 to 2.5 ms, at fixed depolarization levels, Fd had a peak at short pulse duration and low release, and declined with increasing pulse duration and release. This dependence is expected if facilitation is caused by 'residual Ca'. Alternatively, if at fixed duration depolarization in the pulses was increased from threshold level, in most preparations Fd rose to a maximum at low depolarization and release, declined to a minimum at the depolarization level of Fc, and rose again for larger depolarizations. In some preparations, and for short pulses, the peak of Fd at low depolarizations was not observed, but always Fd increased with depolarization beyond Fc. The complicated dependence of Fd on depolarization can be explained by the residual Ca theory, if at depolarizations larger than that which produced Fc and the minimum of Fd, Ca-inflow decreases.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Neurotransmitter release and its facilitation in crayfish. VII. Another voltage dependent process beside Ca entry controls the time course of phasic release.

Quantal synaptic currents were recorded at nerve terminations on the opener muscle of crayfish using a macro-patch-clamp electrode, and the release was elicited by depolarizing current pulses applied to the terminal through the same electrode. After 2 ms depolarization pulses at low temperature, release started with about 2 ms delay after the onset of depolarization, and the maximum rate of release occurred at about 4 ms delay. Large variations in Ca inflow during the pulses were concluded from the facilitation of test EPSCs. The time course of release proved to be remarkably invariant in spite of large changes in release. If a conditioning train of depolarization pulses preceded the test pulse, release due to the test pulse was facilitated up to 60-fold, but the shapes of distributions of quantal delays were practically not affected by this facilitation. Facilitation by the conditioning trains must have raised the [Ca]i level at the onset of the test pulse. The invariance of the time course of release with respect to the level of [Ca]i cannot be explained by theories in which [Ca]i alone controls the time course of release. The time courses of reactions controlling release were explored by mathematical analysis and simulation. A reaction scheme in which the activation of "release sites" directly by depolarization had rate limiting control on the release reactions, in which rise of [Ca]i only was a promoting cofactor, and in which a cooperative reaction involving the complex of release sites and Cai, (SCai) was one of the final steps eliciting release, was able to predict the delayed onset of release and the substantial latency between the end of the depolarization pulse and the maximum of the rate of release. Reaction schemes in which the direct effect of depolarization on release occurred at one or more steps following the entry of Ca could be excluded generally by showing conflict with the experimental findings.

Animals↗