Biomedical subjects

N Akaike

Publications and source records attributed to N Akaike.

At least 307 records · Page 17Linked to original sources

PubMed1988

Permeability to various cations of the voltage-dependent sodium channel of isolated rat hippocampal pyramidal neurons.

The permeability to various cations of the voltage-dependent sodium channel of isolated rat hippocampal pyramidal neurons was investigated under the voltage-clamp condition. The neurons were dispersed enzymatically and mechanically and perfused internally using a suction pipette technique. The permeability sequence, estimated from the reveral potential of the inward current was Li+ greater than Na+ greater than hydrazine+ greater than formamidine+ greater than guanidine+ greater than methylguanidine+ greater than monomethylamine+. Thus the ionic selectivity of the voltage-dependent sodium channel of rat central nervous system neurons is similar to that in the squid axon, myelinated frog nerve fiber and rat ventricle muscle.

Animals↗

PubMed1988

Blockade of N-methyl-D-aspartate response in enzyme-treated rat hippocampal neurons.

The responses to excitatory and inhibitory amino acids have been investigated in isolated pyramidal cells from young and adult rat hippocampus using internal perfusion and 'concentration-clamp' techniques. The neurons dissociated in a purely mechanical way were sensitive to all excitatory amino acids (glutamate, kainate, quisqualate and N-methyl-D-aspartate (NMDA] and inhibitory amino acids (glycine, taurine and gamma-aminobutyric acid). The NMDA response was dramatically potentiated by adding glycine at threshold concentration (10(-6) M). The enzyme treatment of hippocampal slices selectively removed the NMDA sensitivity but did not alter all other pharmacological properties of voltage- and agonist-gated ion channels.

Animals↗

PubMed1988

Ca2+-mediated suppression of the GABA-response through modulation of chloride channel gating in frog sensory neurones.

A suppressant effect of intracellular free Ca2+ on the gamma-aminobutyric acid (GABA)-induced chloride inward current (ICI(GABA)) was studied in isolated frog sensory neurones under whole cell voltage clamp. Voltage-dependent Ca2+ influx elicited during the steady state of ICI(GABA)-induced a fast, slowly recovering current relaxation in the outward direction, the amplitude of which was dependent on total Ca2+ influx. This suppressant effect showed specificity for different divalent cations, suggesting action at a specific intracellular effector. Single channel recording revealed a Ca2+-dependent decrease in the duration of the open time of the GABA-gated Cl- channel without change in single channel conductance.

Animals↗

PubMed1988

Some properties of inhibitory action of lidocaine on the Ca2+ current of single isolated frog sensory neurons.

The action of lidocaine on the Ca2+ current (ICa) was studied on single isolated neurons of frog dorsal root ganglia using a 'concentration-clamp' technique which combines intracellular perfusion with a rapid external solution change. Lidocaine decreased the peak amplitude of ICa at a threshold concentration of 10 microM. Higher concentrations gave a dose-dependent increase in inhibition of ICa. Lidocaine also depressed the Na+ current (INa) at a threshold concentration 10 times lower than that for decreasing the amplitude of ICa of neurons isolated from same ganglia. The rate of inhibitory action on ICa was slowed at more negative holding potentials (VH). Lidocaine appears to block both closed and open Ca2+ channels, but acts more profoundly on open channels.

Animals↗

PubMed1988

Separation of current- and voltage-dependent inactivation of calcium current in frog sensory neuron.

The inactivation process of the calcium current was studied in frog dorsal root ganglion cells using a newly developed 'concentration clamp' technique, and an inactivation component independent of Ca influx was separated from the Ca-dependent component. The neuron was first placed in Ca-free solution, and pre-pulses of various amplitude were applied, thereby inducing depolarization without the Ca influx. Successive test pulses were applied immediately after a rapid exchange to a solution containing normal Ca. The amount of inactivation under this condition was much smaller than that measured when both pre- and test pulses were applied in the normal solution, and reached a steady level on pre-pulses over +50 mV. We suggest that the inactivation process of the Ca current consists of two components, i.e. a dominant component which is dependent on Ca influx, and a smaller one which is presumably voltage-dependent.

Animals↗

PubMed1988

Kinetic analysis of acetylcholine-induced chloride current in isolated Aplysia neurones.

(1) Kinetics of activation and desensitization phases of the ACh-induced chloride current (ICl) were studied in isolated single neurones of Aplysia kurodai, using the 'concentration clamp' technique which combines internal perfusion and rapid exchange of the external solution within a few milliseconds (2) The dose-response curve for the peak ICl gave a dissociation constant of 6.7 X 10(-6) M and a Hill coefficient of 1.7. (3) The current-voltage relationship was linear in the voltage range examined (-70 to +30 mV). The reversal potential (EACh) was -7.1 +/- 1.8 mV (n = 14). The value was close to the calculated equilibrium potential for chloride ions (ECl). (4) The activation phase of the ICl was single exponential and the desensitization proceeded double exponentially to a steady state level. The time constants of both phases decreased with increasing concentrations of ACh but showed no potential dependency. The desensitizing component of the ICl was generated by activation of a single population of the receptor-channel complex. (5) The recovery from desensitization of the ICl induced by 6 X 10(-6) M ACh proceeded double exponentially, with time constants of 6.5 and 43 s at a holding potential of -30 mV. (6) Noise analysis performed on the steady state of ICl induced by low concentrations of ACh (3 X 10(-7) M to 3 X 10(-6) M) showed that the steady ICl was due to activation of a single population of the receptor-channel complex with a single channel conductance of 23.3 +/- 4.3 pS (n = 9).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1988

Kinetic analysis of acetylcholine-induced chloride current in isolated snail neurons.

1. Kinetics of activation and desensitization phases of the acetylcholine (ACh)-induced chloride current (ICI) were studied using isolated single neurons of Japanese land snail and the "concentration clamp" technique. 2. The dose-response curve for the peak ICI gave a dissociation constant of 7.1 x 10(-6) M and a Hill coefficient of 1.8. 3. The current-voltage relationship was linear in the voltage range examined (-60 to +10 mV) and the reversal potential (EACh) was -7.2 +/- 1.5 mV (N = 10). The value was close to the calculated equilibrium potential for chloride ions (ECI). 4. Both activation and desensitization phases of the ACh-induced ICI consisted of a single exponential at concentrations less than 3 x 10(-6) M and a double exponential at higher concentrations. The time constants of both phases decreased with increasing ACh concentrations but showed no potential dependency. 5. The recovery from desensitization of the ICI induced by 5 x 10(-6) M ACh proceeded double exponentially, with time constants of 11 and 114 sec at a holding potential of -30 mV. 6. Noise analysis was performed on a steady-state current induced by 3 x 10(-7) to 2 x 10(-6) M ACh. The mean open time was about 60 msec at 10(-6) M ACh and the single-channel conductance was 14 PS. 7. These results suggest that the ACh receptor-Cl channel complex in snail neurons has two binding sites with the dissociation constant of 7.1 x 10(-6) M and is rapidly activated and desensitized to a steady level in the presence of the agonist.

Acetylcholine↗

PubMed1988

Strychnine decreases the voltage-dependent Ca2+ current of both Aplysia and frog ganglion neurons.

1. The effects of strychnine on the voltage-dependent Ca2+ current (ICa) were studied in physically isolated Aplysia neurons and enzymatically dissociated frog sensory neurons of the dorsal root ganglion. Neurons were studied under the internal perfusion and the voltage clamp condition. 2. Strychnine decreased the ICa with threshold concentrations for effect at 1 to 10 microM. The depression of ICa increased with strychnine dose without effects on the current-voltage relation of ICa. The effects of low concentrations of strychnine were reversible, but recovery was incomplete at higher concentrations. The potency of strychnine was about 10 times less than that of diltiazem, an organic Ca2+ antagonist. At 100 microM the ICa of Aplysia neurons was reduced to about half of the control. This concentration of strychnine also reduced the peak amplitude of ICa of frog sensory neurons. 3. These results indicate that, in addition to its actions on transmitter responses and on Na+ and K+ currents, strychnine has effects on ICa that have not previously been appreciated.

Animals↗

PubMed1988

Differential effects of enflurane on Glu- and ACH-induced chloride currents in Aplysia neurons.

The primary site of anesthetic action remains controversial. In addition to non-specific actions of hydrophobic substances on the membrane, specific effects of volatile anesthetics on neuronal activity have been reported. In the present study, effects of enflurane on the chloride currents (ICl) induced by L-glutamic acid (Glu) and acetylcholine (ACh) in isolated Aplysia neurons were examined, using the 'concentration clamp' technique. Enflurane increased the peak amplitude of the ICl induced by low concentrations of Glu but decreased those evoked by higher concentrations of the agonist. The anesthetic accelerated both activation and desensitization phases of the Glu-induced ICl. On the other hand, the ACh-induced ICl in the same neuron was depressed in an uncompetitive manner in the presence of enflurane. The desensitization phase was not affected, although the activation phase became more rapid and the mean open time obtained by noise analysis was shortened. These results suggest the existence of specific steps in the process of activation and desensitization of channels, at which the volatile anesthetic exerts differential effects on the postsynaptic currents.

Acetylcholine↗

PubMed1988

Piriform cortex brain slices: techniques for isolation of synaptic inputs.

Methods are described for preparation of 3 different slices of piriform cortex which allow convenient study of pyramidal neurons and segregation of synaptic inputs. In slices cut parallel to the pyramidal neurons (perpendicular to the brain surface) one can study chemosensitivity of the various parts of the dendritic tree and the soma. By selected division of this slice the population postsynaptic response to activation of the lateral olfactory tract can be studied without action potential generation. Alternatively the superficial lateral olfactory tract can be removed. Stimulation of deeper regions of the slice under these circumstances elicits a pharmacologically different excitation which appears to be that of association fibers.

Aminobutyrates↗

PubMed1988

Intracellular picrotoxin blocks pentobarbital-gated Cl- conductance.

Using the 'inside-out' configuration of frog sensory neurons, we studied the effect of intracellular picrotoxin on the pentobarbital-gated single channel response of Cl- -current (iCl). The pentobarbital-induced iCl showed no voltage-dependency and the single channel conductance (gamma Cl) was 16 +/- 3.1 pS (n = 6). Picrotoxin caused the pentobarbital-gated Cl- channels to react in a flickering pattern and then finally caused them to cease their opening altogether. This inhibitory action of picrotoxin was reversible.

Animals↗

PubMed1988

Inhibition of the voltage-dependent calcium currents in isolated frog sensory neurons by GABA-related agonistic compounds.

Effects of GABAA-, barbiturate- and benzodiazepine receptor agonists and GABAB agonist, baclofen, on voltage-dependent Ca2+ current (ICa) were studied in isolated frog sensory neurons after suppression of Na+ and K+ currents using single-electrode voltage-clamp. GABA, muscimol, taurine and pentobarbital (PB) dose-dependently induced a transient Cl- current (ICl), while baclofen and diazepam (DZP) did not elicit any currents. With GABAA agonists such as GABA, muscimol and taurine, ICa was suppressed transiently, and the maximum inhibition of ICa occurred within 1 min. The suppression of ICa by all GABAA agonists was neither voltage dependent nor attenuated in the presence of either bicuculline or picrotoxin. In addition, there was no correlation between GABA- and baclofen-induced suppressions of ICa. The results suggest that the inhibition of ICa by GABAA receptor agonists is not due to either GABAA or GABAB receptor activation at least. The inhibition of ICa by baclofen, PB and DZP was persistent. PB suppressed the amplitude of ICa and also facilitated the inactivation process, suggesting that PB behaves as a Ca channel blocker. However, the mechanisms of ICa suppression by baclofen and DZP are the subject for a future study. The potency order of the drugs in reducing ICa was muscimol greater than GABA = DZP greater than baclofen greater than PB greater than taurine.

Animals↗

PubMed1988

Electrophysiological detection of acetylcholinesterase activity using concentration clamp on physically isolated Aplysia neurons.

In this study, we have used electrophysiological techniques to evaluate the acetylcholinesterase (AChE) activity on single neurons physically isolated from the pedal ganglia of Aplysia californica and kurodai. Acetylcholine (ACh) was applied to cells having Na-dependent response using a concentration clamp technique which allows a step-like complete change of external medium around the cell (diameter more than 120 micron) within 30 msec. When the neuron was exposed to ACh (50 microM) initially by rapid and brief (400-800 msec) flow and continuously after stopping the perfusion, the induced current rose to a peak and then decayed in the presence of ACh. However, the current increased again when the rapid flow of the same ACh solution around the cell was resumed. The increase in the current by the resumption of the perfusion was not seen when carbachol was substituted for ACh or when extraordinarily high concentration (10 mM) of ACh was used. Furthermore, this increase in the current was blocked by the antiAChE agent, edrophonium, in a dose-dependent manner. These results suggest that acetylcholinesterase (AChE) causes a local depletion of ACh at the membrane surface where the rate of hydrolysis of ACh exceeds the rate of ACh diffusion from bulk solution and the increase in the current by the resumption of the perfusion resulted from the restoration of ACh concentration at the membrane surface. This electrophysiological indication of AChE activity may be a useful tool for the study of AChE by other than biochemical means.

Acetylcholine↗

PubMed1988

Blockade of gamma-aminobutyric acid-gated chloride current in frog sensory neurons by picrotoxin.

The mechanism of picrotoxin (PTX) suppression of the gamma-aminobutyric acid (GABA)-gated Cl- current (ICl) was examined in frog sensory neurons using the 'concentration-clamp' technique. The activation phase of GABA-induced ICl showed little change with the concomitant application of 10(-5) M PTX; however, the inactivation phase was markedly facilitated. ICl produced by simultaneous application of GABA and PTX was non-competitively suppressed while the plateau current showed a mixed type of competitive and non-competitive inhibitions. When the neuron was pretreated with PTX, the peak current of ICl produced by the simultaneous application of PTX and GABA was gradually suppressed, but the suppression of plateau level of ICl was rapid and not affected by pretreatment time. Recovery was not influenced by the length of pretreatment but depended only slightly on wash time. A major part of recovery occurred through the reactivation of the inhibited GABA receptor-ionophore complex by GABA. The first application of 3 x 10(-6) M GABA, after the response to 3 x 10(-6) M GABA was suppressed by the concomitant application of PTX, produced ICl consisting of the rapid phase and the slowly developing phase. ICl produced by simultaneous application of 10(-5) M GABA and 10(-5) M PTX and by the first application of 10(-5) M GABA after the inhibition showed a similar voltage dependence to the control ICl. These results indicate that PTX has access to the binding site inside the Cl- channel either through open channels or with different efficacies through closed channels, and thereby inhibits the GABA response by modifying the gating process.

Animals↗

PubMed1988

Mechanical and enzymatic isolation of mammalian CNS neurons.

Neurons were isolated from various regions of the central nervous system (CNS), by both enzymatic and mechanical isolation. These neurons were isolated from the brains of 3-21-day-old and adult rats, guinea pigs and kittens. Particular attention was directed to the thickness of the slice, the enzymes used and the treatment time, the ionic composition, pH and buffer of the bathing medium, the pipetting of brain slices after enzyme treatment, and the preservation of the isolated cells. The isolated neurons had long dendrites with numerous branchings and a typical morphological shape: e.g. the pyramidal neurons of the rat hippocampus had apical dendrites over 250 micron long; those of the rat neocortex had apical dendrites longer than 300 micron; the Purkinje cells of the rat and kitten also maintained dendrites with fifth branchings. All isolated neurons had well-preserved electrical and chemical membrane properties of the voltage-dependent channels and the receptor-ionophore complexes respectively, even after the enzyme treatment. Thus, these isolated CNS neurons having a well-preserved morphological state can be used extensively for electrophysiological and pharmacological studies on voltage-dependent and drug-gated ionic channels.

Animals↗

PubMed1988

Inhibition of drug-gated chloride currents by calcium influx in frog sensory neurons.

In isolated and internally perfused frog sensory neurons, muscimol-, pentobarbital- and alpha-chloralose-induced Cl- currents were suppressed by voltage-dependent Ca2+ currents. The amount of chloride currents inhibited by Ca2+ influx developed in a hyperbolic manner as a function of Ca2+ influx. The increase in intracellular Ca2+ concentration also suppressed the currents carried by monovalent anions, such as Br-, I-, NO3- and HCOO-.

Animals↗

PubMed1988

Effects of diuretics on GABA-gated chloride current in frog isolated sensory neurones.

1. Effects of three diuretics (furosemide, amiloride and alpha-human atrial natriuretic polypeptide (alpha-hANP] on GABA-activated chloride current (ICl) were investigated in frog isolated sensory neurones, following suppression of Na+, K+ and Ca2+ currents, by use of a 'concentration-clamp' technique. 2. Furosemide inhibited the GABA-activated ICl in a non-competitive manner and facilitated the inactivation phase, while amiloride inhibited the GABA response in a competitive manner, both inhibitions being concentration-dependent. Alpha-hANP had no effects on the GABA-induced ICl. 3. The reversal potential of GABA-activated ICl (EGABA) was not shifted in the presence of amiloride or furosemide. 4. The results suggest that amiloride may act at the GABA binding site while furosemide may act on the GABA-gated chloride channel.

Amiloride↗

PubMed1988

Effects of neostigmine and physostigmine on the acetylcholine receptor-ionophore complex in frog isolated sympathetic neurones.

1. The effects of neostigmine and physostigmine, reversible carbamate acetylcholinesterase (AChE)-inhibitors, on nicotinic acetylcholine-induced inward currents (IACh) were investigated in enzymatically isolated single sympathetic ganglion cells from the bullfrog. The 'concentration clamp' technique which combines intracellular perfusion with a rapid external solution change under single electrode voltage-clamp conditions was used. 2. Pretreatment with neostigmine and physostigmine did not enhance IACh at any concentrations, suggesting that AChE activity had already disappeared during the enzymatic treatment of the preparation. 3. Both neostigmine and physostigmine inhibited IACh in a dose-dependent manner with IC50 values of 7.0 x 10(-4) M and 1.1 x 10(-4) M, respectively. The blockade by neostigmine was competitive, while that by physostigmine was non-competitive. 4. The inhibition of IACh by neostigmine and physostigmine showed no apparent voltage dependency. 5. Neostigmine did not cause obvious changes of the kinetics of IACh. However, physostigmine reduced both the fast and slow time constants of inactivation of IACh, thus facilitating the rate of inactivation without affecting the activation kinetics of IACh. 6. These results suggest that neostigmine and physostigmine have different direct actions on the ACh receptor-ionophore complex. Neostigmine may act on the ACh-receptor (the binding site of ACh) while physostigmine may interact with the ACh-gated cation channels.

Animals↗