Tonic transmitter release in a graded potential synapse

1995 ◽  
Vol 74 (1) ◽  
pp. 470-473 ◽  
Author(s):  
R. O. Uusitalo ◽  
M. Juusola ◽  
E. Kouvalainen ◽  
M. Weckstrom
Keyword(s):  
Noise Reduction ◽  
Transmitter Release ◽  
Light Adaptation ◽  
Spectral Characteristics ◽  
Reversal Potential ◽  
Input Resistance ◽  
Postsynaptic Membrane ◽  
Resting Potential ◽  
Omega 3 ◽  
Visual Interneuron

1. We studied graded synaptic transmission in the fly photoreceptor-interneuron synapse by using intracellular in situ recordings from pre- and postsynaptic cells. 2. A large presynaptic hyperpolarization after light adaptation, caused by the activation of the electrogenic Na+/K+ pump, drastically reduced the conspicuous postsynaptic dark noise. At the same time, the postsynaptic neurons depolarized, with an increase of input resistance of 5-10 M omega. 3. The spectral characteristics of the postsynaptic membrane noise in dark and during noise reduction, together with the other results, suggested that the transmitter release decreased dramatically approximately 12 mV below the resting potential of the presynaptic photoreceptors. 4. During the postsynaptic noise reduction, the saturated and subsaturated first-order visual interneuron responses were increased up to 9 mV with a time constant of recovery of approximately 10 s. This increase was shown to be caused by the negative shift of the reversal potential of the transmitter-gated (mainly Cl-) conductance, caused apparently by the reduced transmitter input. 5. The results strongly suggest that the photoreceptor transmitter release in fly is tonic, even in dark, and further support the modulation of the synaptic voltage transfer by postsynaptic Cl- extrusion.

Electrical properties of frog motoneurons in the in situ spinal cord

1976 ◽  
Vol 39 (3) ◽  
pp. 459-473 ◽  
Author(s):  
P. C. Magherini ◽  
W. Precht
Keyword(s):  
Spinal Cord ◽  
Membrane Potential ◽  
Electrical Properties ◽  
Rana Temporaria ◽  
Reversal Potential ◽  
Input Resistance ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Spike Initiation

Electrical properties of the spinal motoneurons of Rana temporaria and R. esculenta were investigated in the in situ spinal cord at 20-22 degrees C by means of intracellular recording and current injection. Input resistance values depended on the method of measurement in a given cell but were generally inversely related to axon conduction velocity. The membrane-potential response to a subthreshold current pulse was composed of at least two exponentials with mean time constants of 2.5 and 20 ms. The membrance potential reached by the peak of a spike depended on the mode of spike initiation and membrane potential. Preceding a suprathreshold depolarization by a hyperpolarizing pulse could delay and eliminate spike initiation, similar to effects reported in certain invertebrate neurons. Antidromic invasion frequently failed in motoneurons of normal resting potential. Antidromic spike components (m,IS, SD) were similar to those of cat motoneurons. The delayed depolarization and the long afterhyperpolarization following an antidromic spike had many properties in common with the analogous afterpotentials of cat motoneurons. The reversal potential of the short afterhyperpolarization occurring immediately after the spike varied with resting potential and could not be used to determine potassium equilibrium potential. Sustained rhythmic firing could be evoked by continuous synaptic drive or long pulses of injected current. The plot of firing rate versus current strength had a substantial linear region. Both steady firing and adaptation properties varied markedly with motoneuron input resistance.

Mechanisms of Afterhyperpolarization in Lobster Olfactory Receptor Neurons

1998 ◽  
Vol 80 (3) ◽  
pp. 1268-1276 ◽  
Author(s):  
Frank S. Corotto ◽  
William C. Michel
Keyword(s):  
Voltage Clamp ◽  
Olfactory Receptor ◽  
Reversal Potential ◽  
Input Resistance ◽  
Olfactory Receptor Neurons ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Pipette Solution ◽  
Cation Current ◽  
Receptor Neurons

Corotto, Frank S. and William C. Michel. Mechanisms of afterhyperpolarization in lobster olfactory receptor neurons. J. Neurophysiol. 80: 1268–1276, 1998. In lobster olfactory receptor neurons (ORNs), depolarizing responses to odorants and current injection are accompanied by the development of an afterhyperpolarization (AHP) that likely contributes to spike-frequency adaptation and that persists for several seconds after termination of the response. A portion of the AHP can be blocked by extracellular application of 5 mM CsCl. At this concentration, CsCl specifically blocks the hyperpolarization-activated cation current ( I h) in lobster ORNs. This current is likely to be active at rest, where it provides a constant, depolarizing influence. Further depolarization deactivates I h, thus allowing the cell to be briefly hyperpolarized when that depolarizing influence is removed, thus generating an AHP. Reactivation of I h would terminate the AHP. The component of the AHP that could not be blocked by Cs+ (the Cs+-insensitive AHP) was accompanied by decreased input resistance, suggesting that this component is generated by increased conductance to an ion with an equilibrium potential more negative than the resting potential. The Cs+-insensitive AHP in current clamp and the underlying current in voltage clamp displayed a reversal potential of approximately –75 mV. Both E K and E Cl are predicted to be in this range. Similar results were obtained with the use of a high Cl– pipette solution, although that shifted E Cl from –72 mV to –13 mV. However, when E K was shifted to more positive or negative values, the reversal potential also shifted accordingly. A role for the Ca2+-mediated K+ current in generating the Cs+-independent AHP was explored by testing cells in current and voltage clamp while blocking I K(Ca) with Cs+/Co2+-saline. In some cells, the Cs+-independent AHP and its underlying current could be completely and reversibly blocked by Cs+/Co2+ saline, whereas in other cells some fraction of it remained. This indicates that the Cs+-independent AHP results from two K+ currents, one that requires an influx of extracellular Ca2+ and one that does not. Collectively, these findings indicate that AHPs result from three phenomena that occur when lobster ORNs are depolarized: 1) inactivation of the hyperpolarization-activated cation current, 2) activation of a Ca2+-mediated K+ current, and 3) activation of a K+ current that does not require influx of extracellular Ca2+. Roles of these processes in modulating the output of lobster ORNs are discussed.

The effects of axotomy upon the extrasynaptic acetylcholine sensitivity of an identified motoneurone in the cockroach Periplaneta americana

1982 ◽  
Vol 98 (1) ◽  
pp. 329-341
Author(s):  
J. A. David ◽  
R. M. Pitman
Keyword(s):  
Periplaneta Americana ◽  
Reversal Potential ◽  
Input Resistance ◽  
Resting Potential ◽  
Normal Range ◽  
Threefold Increase ◽  
M 10 ◽  
Low Concentrations ◽  
Acetylcholine Sensitivity ◽  
Soma Membrane

The effects of axotomy on the sensitivity of the fast coxal depressor motoneurone (Df) of the cockroach (Periplaneta americana) to applied acetylcholine (ACh) and carbamylcholine (CCh) have been investigated. ACh and CCh applied to the soma membrane either by bath perfusion or by ionophoresis caused depolarization; repeated application of large doses of these agonists resulted in a relatively rapid desensitization and depression of the response. Axotomy performed 3–10 days before recordings were made caused an approximately threefold increase in the sensitivity to ACh but had no affect upon the sensitivity to CCh. The resting potential, input resistance and membrane time-constant remained within the normal range. In addition there was no change in the rise-times of the responses or of the ACh reversal potential, or in the apparent number of ACh molecules needed to combine with individual cholinoceptors to produce a response. The anticholinesterases physostigmine and neostigmine potentiated the ACh response at relatively low concentrations (10(−7) M-10(−6) M). This potentiation was significantly greater in the normal cells than in the axotomized cells. It is therefore concluded that the increase in ACh sensitivity of this motoneurone results at least partly from a fall in the activity of cholinesterase in the region of the applied drug.

Muscarinic depression of synaptic transmission at the hippocampal mossy fiber synapse

1990 ◽  
Vol 64 (4) ◽  
pp. 1089-1097 ◽  
Author(s):  
S. Williams ◽  
D. Johnston
Keyword(s):  
Synaptic Transmission ◽  
Mossy Fiber ◽  
Reversal Potential ◽  
Input Resistance ◽  
Cesium Chloride ◽  
Resting Potential ◽  
Excitatory Postsynaptic Potential ◽  
Bath Application ◽  
Before And After ◽  
Mossy Fiber Synapse

1. The action of muscarine was studied in the CA3 region of the rat hippocampal slice with single-electrode voltage-clamp techniques. 2. Bath application of 1 or 10 microM muscarine produced an increase in the input resistance of these cells and reduced the slow afterhyperpolarization (sAHP) response. Changes in input resistance were more pronounced around the resting potential of the cell (-50 to -60 mV), but in many cells an effect was also seen at -80 mV. These effects were absent when cesium chloride-containing microelectrodes were used. 3. At 1 microM, muscarine had little effect on synaptic transmission, causing a 0 +/- 7% (mean +/- SE, n = 19) change in excitatory postsynaptic potential (EPSP) and decreasing the excitatory postsynaptic current (EPSC) by 11 +/- 6% (n = 14); neither change was statistically significant. 4. In contrast, 10 microM muscarine produced a reliable depression of both the EPSP and EPSC. This effect was independent of the electrolyte used: with KCl the EPSP was depressed 23 +/- 4% (n = 5) and the EPSC 35 +/- 5% (n = 4); for CsCl the EPSP was depressed 23 +/- 10% (n = 7) and the EPSC 34 +/- 5% (n = 7). 5. Muscarine did not alter the reversal potential of the synaptic current but merely produced a decrease in slope conductance (37 +/- 5%, n = 6). 6. Muscarine did not significantly alter the shape of the EPSC waveform. This was assessed by comparing the 10-90% rise time and the half decay time of the current before and after muscarine.(ABSTRACT TRUNCATED AT 250 WORDS)

Inward rectification in the inner segment of single retinal cone photoreceptors

1990 ◽  
Vol 64 (6) ◽  
pp. 1917-1928 ◽  
Author(s):  
A. V. Maricq ◽  
J. I. Korenbrot
Keyword(s):  
Voltage Dependence ◽  
Reversal Potential ◽  
Input Resistance ◽  
Resting Potential ◽  
Inward Rectification ◽  
Delayed Rectifier ◽  
Light Illumination ◽  
Cone Photoreceptors ◽  
Voltage Dependent ◽  
Kinetics Of

1. Single cone photoreceptors were dissociated from the retina of a lizard with the aid of papain. The majority of the cells lost their outer segments but had well-preserved, large synaptic pedicles. Electrical properties of the cells were studied with tight-seal electrodes in the whole cell configuration. On the average, cone inner segments had a resting potential of -55 mV, and at this potential their input resistance was 2.6 G omega and their capacitance was 8 pF. 2. Under current clamp the cones exhibited a pronounced anomalous voltage rectification in response to hyperpolarizing currents. The voltage rectification was eliminated by external Cs+. 3. The Cs(+)-sensitive current underlying voltage rectification was isolated by blocking other currents present in the cone. Co2+ blocked a voltage-dependent Ca2+ current and a Ca2(+)-dependent Cl- current, and tetraethylammonium (TEA)+ blocked a delayed-rectifier K+ current. 4. The Cs(+)-sensitive current was activated by hyperpolarization to potentials more negative than -50 mV, and its current-voltage (I-V) relationship exhibited inward rectification. 5. The inward-rectifying current was selective for K+, but not exclusively. Increasing external K+ concentration 10-fold shifted the reversal potential by 13 mV. If Na ions also permeate through the inward-rectifying channels, the ratio of permeabilities (PK+/PNa+) in normal solution is approximately 3.9. 6. The kinetics of the inward-rectifying current were described by the sum of two exponentials, the amplitudes and time constants of which were voltage dependent. 7. The voltage dependence of the inward-rectifying current was described by Boltzmann's function, with half-maximum activation at -79 mV and a steepness parameter of 7.5 mV. 8. The voltage dependence and kinetics of the inward-rectifying current suggest that it is inactive in a cone photoreceptor in the dark. However, it becomes activated in the course of large hyperpolarizations generated by bright-light illumination. This activity will modify the waveform of the photovoltage--the current will generate a depolarizing component that opposes the light-generated hyperpolarization.

scholarly journals Two light-dependent conductances in Lima rhabdomeric photoreceptors.

1991 ◽  
Vol 97 (1) ◽  
pp. 55-72 ◽  
Author(s):  
E Nasi
Keyword(s):  
Light Adaptation ◽  
Late Phase ◽  
Reversal Potential ◽  
Membrane Conductance ◽  
Light Response ◽  
Light Sensitivity ◽  
Resting Potential ◽  
Test Flash ◽  
Ionic Selectivity ◽  
Subsequent Test

Light-dependent membrane currents were recorded from solitary Lima photoreceptors with the whole-cell clamp technique. Light stimulation from a holding voltage near the cell's resting potential evokes a transient inward current graded with light intensity, accompanied by an increase in membrane conductance. While the photocurrent elicited by dim flashes decays smoothly, at higher stimulus intensities two kinetically distinct components become visible. Superfusion with TEA or intracellular perfusion with Cs do not eliminate this phenomenon, indicating that it is not due to the activation of the Ca-sensitive K channels that are present in these cells. The relative amplitude of the late component vs. the early peak of the light response is significantly more pronounced at -60 mV than at -40 mV. At low light intensities the reversal potential of the photocurrent is around 0 mV, but with brighter lights no single reversal potential is found; rather, a biphasic response with an inward and an outward component can be seen within a certain range of membrane voltages. Light adaptation through repetitive stimulation with bright flashes diminishes the amplitude of the early but not the late phase of the photocurrent. These observations can be accounted for by postulating two separate light-dependent conductances with different ionic selectivity, kinetics, and light sensitivity. The light response is also shown to interact with some of the voltage-sensitive conductances: activation of the Ca current by a brief conditioning prepulse is capable of attenuating the photocurrent evoked by a subsequent test flash. Thus, Ca channels in these cells may not only shape the photoresponse, but also participate in the process of light adaptation.

Properties of visceral primary afferent neurons in the nodose ganglion of the rabbit

1985 ◽  
Vol 54 (2) ◽  
pp. 245-260 ◽  
Author(s):  
C. E. Stansfeld ◽  
D. I. Wallis
Keyword(s):  
Action Potentials ◽  
Input Resistance ◽  
Nodose Ganglion ◽  
Time Dependent ◽  
Membrane Properties ◽  
Resting Potential ◽  
Inward Rectification ◽  
C Cells ◽  
Axonal Conduction ◽  
A Cells

The active and passive membrane properties of rabbit nodose ganglion cells and their responsiveness to depolarizing agents have been examined in vitro. Neurons with an axonal conduction velocity of less than 3 m/s were classified as C-cells and the remainder as A-cells. Mean axonal conduction velocities of A- and C-cells were 16.4 m/s and 0.99 m/s, respectively. A-cells had action potentials of brief duration (1.16 ms), high rate of rise (385 V/s), an overshoot of 23 mV, and relatively high spike following frequency (SFF). C-cells typically had action potentials with a "humped" configuration (duration 2.51 ms), lower rate of rise (255 V/s), an overshoot of 28.6 mV, an after potential of longer duration than A-cells, and relatively low SFF. Eight of 15 A-cells whose axons conducted at less than 10 m/s had action potentials of longer duration with a humped configuration; these were termed Ah-cells. They formed about 10% of cells whose axons conducted above 2.5 m/s. The soma action potential of A-cells was blocked by tetrodotoxin (TTX), but that of 6/11 C-cells was unaffected by TTX. Typically, A-cells showed strong delayed (outward) rectification on passage of depolarizing current through the soma membrane and time-dependent (inward) rectification on inward current passage. Input resistance was thus highly sensitive to membrane potential close to rest. In C-cells, delayed rectification was not marked, and slight time-dependent rectification occurred in only 3 of 25 cells; I/V curves were normally linear over the range: resting potential to 40 mV more negative. Data on Ah-cells were incomplete, but in our sample of eight cells time-dependent rectification was absent or mild. C-cells had a higher input resistance and a higher neuronal capacitance than A-cells. In a proportion of A-cells, RN was low at resting potential (5 M omega) but increased as the membrane was hyperpolarized by a few millivolts. A-cells were depolarized by GABA but were normally unaffected by 5-HT or DMPP. C-cells were depolarized by GABA in a similar manner to A-cells but also responded strongly to 5-HT; 53/66 gave a depolarizing response, and 3/66, a hyperpolarizing response. Of C-cells, 75% gave a depolarizing response to DMPP.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of ouabain on background and voltage-dependent currents in canine colonic myocytes

1990 ◽  
Vol 259 (3) ◽  
pp. C402-C408 ◽  
Author(s):  
E. P. Burke ◽  
K. M. Sanders
Keyword(s):  
Membrane Potential ◽  
Potential Gradient ◽  
Circular Muscle ◽  
Input Resistance ◽  
Pump Current ◽  
Muscle Layer ◽  
Membrane Properties ◽  
Resting Potential ◽  
Voltage Dependent ◽  
In Cells

Previous studies have suggested that the membrane potential gradient across the circular muscle layer of the canine proximal colon is due to a gradient in the contribution of the Na(+)-K(+)-ATPase. Cells at the submucosal border generate approximately 35 mV of pump potential, whereas at the myenteric border the pump contributes very little to resting potential. Results from experiments in intact muscles in which the pump is blocked are somewhat difficult to interpret because of possible effects of pump inhibitors on membrane conductances. Therefore, we studied isolated colonic myocytes to test the effects of ouabain on passive membrane properties and voltage-dependent currents. Ouabain (10(-5) M) depolarized cells and decreased input resistance from 0.487 +/- 0.060 to 0.292 +/- 0.040 G omega. The decrease in resistance was attributed to an increase in K+ conductance. Studies were also performed to measure the ouabain-dependent current. At 37 degrees C, in cells dialyzed with 19 mM intracellular Na+ concentration [( Na+]i), ouabain caused an inward current averaging 71.06 +/- 7.49 pA, which was attributed to blockade of pump current. At 24 degrees C or in cells dialyzed with low [Na+]i (11 mM), ouabain caused little change in holding current. With the input resistance of colonic cells, pump current appears capable of generating at least 35 mV. Thus an electrogenic Na+ pump could contribute significantly to membrane potential.

Calcium-dependent potassium conductance in rat supraoptic nucleus neurosecretory neurons

1985 ◽  
Vol 54 (6) ◽  
pp. 1375-1382 ◽  
Author(s):  
C. W. Bourque ◽  
J. C. Randle ◽  
L. P. Renaud
Keyword(s):  
Time Constant ◽  
Action Potentials ◽  
Supraoptic Nucleus ◽  
Potassium Conductance ◽  
Reversal Potential ◽  
Input Resistance ◽  
Mean Amplitude ◽  
Progressive Increase ◽  
Calcium Dependent ◽  
Neurosecretory Neurons

Intracellular recordings of rat supraoptic nucleus neurons were obtained from perfused hypothalamic explants. Individual action potentials were followed by hyperpolarizing afterpotentials (HAPs) having a mean amplitude of -7.4 +/- 0.8 mV (SD). The decay of the HAP was approximated by a single exponential function having a mean time constant of 17.5 +/- 6.1 ms. This considerably exceeded the cell time constant of the same neurons (9.5 +/- 0.8 ms), thus indicating that the ionic conductance underlying the HAP persisted briefly after each spike. The HAP had a reversal potential of -85 mV and was unaffected by intracellular Cl- ionophoresis of during exposure to elevated extracellular concentrations of Mg2+. In contrast, the peak amplitude of the HAP was proportional to the extracellular Ca2+ concentration and could be reversibly eliminated by replacing Ca2+ with Co2+, Mn2+, or EGTA in the perfusion fluid. During depolarizing current pulses, evoked action potential trains demonstrated a progressive increase in interspike intervals associated with a potentiation of successive HAPs. This spike frequency adaptation was reversibly abolished by replacing Ca2+ with Co2+, Mn2+, or EGTA. Bursts of action potentials were followed by a more prolonged afterhyperpolarization (AHP) whose magnitude was proportional to the number of impulses elicited (greater than 20 Hz) during a burst. Current injection revealed that the AHP was associated with a 20-60% decrease in input resistance and showed little voltage dependence in the range of -70 to -120 mV. The reversal potential of the AHP shifted with the extracellular concentration of K+ [( K+]o) with a mean slope of -50 mV/log[K+]o.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiological effects of two FMRFamide-related peptides from the crayfish Procambarus clarkii

1995 ◽  
Vol 198 (1) ◽  
pp. 109-116
Author(s):  
M Skerrett ◽  
A Peaire ◽  
P Quigley ◽  
A Mercier
Keyword(s):  
Transmitter Release ◽  
Procambarus Clarkii ◽  
Neuromuscular Junctions ◽  
Input Resistance ◽  
Physiological Effects ◽  
Synaptic Current ◽  
Extensor Muscles ◽  
Neuromuscular Systems ◽  
Dose Dependent ◽  
Measurable Change

The present study examined the effects of two recently identified neuropeptides on crayfish hearts and on neuromuscular junctions of the crayfish deep abdominal extensor muscles. The two peptides, referred to as NF1 (Asn-Arg-Asn-Phe-Leu-Arg-Phe-NH2) and DF2 (Asp-Arg-Asn-Phe-Leu-Arg-Phe-NH2), increased the rate and amplitude of spontaneous cardiac contractions and increased the amplitude of excitatory junctional potentials (EJPs) in the deep extensors. Both effects were dose-dependent, but threshold and EC50 values for the cardiac effects were at least 10 times lower than for the deep extensor effects. The heart responded equally well to three sequential applications of peptide in any given preparation, but the responses of the deep extensors appeared to decline with successive peptide applications. The results support the hypothesis that these two neuropeptides act as neurohormones to modulate the cardiac and neuromuscular systems in crayfish. Quantal synaptic current recordings from the deep extensor muscles indicate that both peptides increase the number of quanta of transmitter released from synaptic terminals. Neither peptide elicited a measurable change in the size of quantal synaptic currents. NF1 caused a small increase in muscle cell input resistance, while DF2 did not alter input resistance. These data suggest that DF2 increases EJP amplitudes primarily by increasing transmitter release, while the increase elicited by NF1 appears to involve presynaptic and postsynaptic mechanisms.

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