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K Koketsu

Publications and source records attributed to K Koketsu.

At least 19 recordsLinked to original sources
PubMed1988

Indirect effects of acetylcholine on the electrogenic sodium pump in bull-frog atrial muscle fibres.

1. Effects of acetylcholine (ACh) on the activity of electrogenic Na+ pump in bullfrog atrial muscle fibres were examined using the single sucrose-gap voltage clamp technique. 2. In the K+-free solution, 10 microM-ACh induced a large outward current (ACh-induced current) with an increase in the membrane conductance. 3. The amplitude of the ACh-induced current decreased to 15% of the control 10 min after application of 1 microM-ouabain, suggesting the contribution of electrogenic Na+ pump to the ACh-induced current. The remaining ACh-induced current was not affected even if the concentration of ouabain was increased ten times. 4. The K+-activated current induced by an activation of the electrogenic Na+ pump was suppressed or reversed its direction during the course of the ACh-induced current. 5. The ACh-induced current was completely inhibited by applications of either atropine or barium ions while the K+-activated current was not affected. 6. Both ouabain-sensitive and -insensitive ACh-induced currents were decreased when the membrane was hyperpolarized and eliminated around -95 mV. 7. The ouabain-sensitive component was decreased by increasing the external K+ concentration [K+]o; the proportions of this current to ACh-induced current in 0.5, 0.75, 1 and 2 mM [K+]o were 54, 42, 34 and 14%, respectively. 8. The current-voltage (i-v) relation obtained in 2 or 4 mM [K+]o, where the currents carried by Na+ and Ca2+ were blocked by application of 1 microM-TTX and 1 mM-Cd2+, exhibits marked inward-going rectification but does not show a clear N-shaped feature. Ba2+ (1 mM) induced an inward current at the holding potential (-80 mV) and eliminated the inward-going rectification of the membrane. 9. These results suggest that the increase in the K+ permeability by ACh increases the concentration of K+ immediately outside of the membrane, which in turn stimulates the electrogenic Na+ pump mechanism. The physiological significance of the action of ACh on the electrogenic Na+ pump in bull-frog atrium is discussed in relation to the background K+ current (IK,1).

Acetylcholine↗
PubMed1987

Evidence for epinephrine-induced depolarization in neurons of bullfrog sympathetic ganglia.

The response to epinephrine (EP) was determined for neurons in bullfrog sympathetic ganglia by intracellular and voltage-clamp recording techniques. EP (5 microM-1 mM) produced a concentration-dependent depolarization mediated through beta-adrenoceptors. The EP-induced depolarization (EPD) was associated with a decrease in the membrane conductance. The EP-induced current (EP1) was decreased at hyperpolarizing potential levels and nullified at -70 mV. No reversal of the EPI polarity was seen. It is concluded that the EPD is generated by the suppression of a voltage-dependent gK, probably the M-channel.

Adrenergic alpha-Antagonists↗
PubMed1987

Highly sensitive analysis of gangliosides in human cerebrospinal fluid with neurological diseases.

We have developed a new method for detection and determination of ganglio-series gangliosides by TLC/enzyme-immunostaining. By using this method, even 1 pmole of the gangliosides in cerebrospinal fluid (CSF) from gangliosidoses and other neurological patients could be measured quantitatively. The accumulation of the gangliosides in CSF was demonstrated from patients with gangliosidoses, thus, the diagnosis could be confirmed antemortem.

Antibodies↗
PubMed1986

Sensitive enzyme-immunostaining and densitometric determination of ganglio-series gangliosides on thin-layer plate: pmol detection of gangliosides in cerebrospinal fluid.

An immunochemical method has been developed for sensitive detection and determination of ganglio-series gangliosides using thin-layer chromatography/enzyme-immunostaining. After chromatography of gangliosides, the plate was treated with Arthrobacter ureafaciens sialidase to remove all sialic acids from ganglio-series gangliosides. For the complete hydrolysis of gangliosides, sodium taurodeoxycholate was found to be required. The resulting asialo-glycolipids, GA2 and GA1 were reacted first with affinity-purified anti-GA2 and anti-GA1, respectively, and second with horseradish peroxidase-conjugated anti-rabbit IgG. Being highly sensitive and reproducible, it allows the characterization of gangliosides in cerebrospinal fluid which cannot be detected by classical methods.

Animals↗
PubMed1986

5-Hydroxytryptamine decreases the sensitivity of nicotinic acetylcholine receptor in bull-frog sympathetic ganglion cells.

The post-synaptic effects of 5-hydroxytryptamine (5-HT) were examined in neurones of bull-frog sympathetic ganglia with intracellular micro-electrode and voltage-clamp recording techniques. Atropine (1 microM) was used to block the muscarinic cholinoceptors. 5-HT reduced the amplitude of the fast excitatory post-synaptic potential (fast e.p.s.p.). 5-HT also reduced the mean amplitude of the miniature excitatory post-synaptic potentials (m.e.p.s.p.s) without affecting their frequency. Voltage-clamp studies showed that 5-HT decreased in a dose-dependent manner the amplitude of the acetylcholine (ACh) current produced by ionophoretic application of ACh to sympathetic neurones. The relationship between the log of the ACh dose, applied ionophoretically, and the peak ACh current (the dose-response curve) was examined in voltage-clamped neurones. 5-HT caused a parallel shift to the right of the dose-response curve for ACh. Analysis using a double reciprocal plot (Lineweaver-Burk plot) revealed that 5-HT increased the apparent dissociation constant (Km) of ACh for the receptor without changing the maximum ACh current (Vmax), suggesting a competitive antagonism. The relationship between the 5-HT dose and the magnitude of inhibition of the ACh current was obtained using two different amplitudes for the ACh response. The dose-response curve of 5-HT-induced inhibition using a relatively high amplitude ACh current, S1, was parallel with that for a relatively low amplitude ACh current, S2. The Dixon plot of these two curves yielded an apparent inhibition constant (Ki) of 42 microM. Both fast excitatory post-synaptic currents (fast e.p.s.c.s) and miniature excitatory post-synaptic currents (m.e.p.s.c.s) had single-exponential decay time courses. The time constants of fast e.p.s.c. decay (tau e) and m.e.p.s.c. decay (tau m) were not altered by 5-HT, suggesting that 5-HT does not change the kinetics of opening and closing of the ionic channel associated with the nicotinic receptor. 5-HT did not alter the reversal potential of the fast e.p.s.c. These results suggest that 5-HT decreases the sensitivity of the nicotinic receptor of sympathetic neurones, by interfering with ACh binding at the active site on the receptor-ionic-channel complex. 5-HT may physiologically inhibit cholinergic transmission as it is an endogenous substance which antagonizes the nicotinic receptor in post-ganglionic neurones of bull-frog sympathetic ganglia.

Acetylcholine↗
PubMed1985

Beta-adrenergic modulation of the Na+-K+ pump in frog skeletal muscles.

Adrenaline markedly increased the ouabain-sensitive 22Na+-efflux by stimulating the Na+-K+ pump in frog skeletal muscle. The facilitatory effects of adrenaline had the following properties. The effects of adrenaline on the ouabain-sensitive Na+-efflux were observed at concentrations greater than 0.1 microM and the magnitude increased with concentration up to 10 microM. At a concentration of 30 microM, adrenaline markedly augmented the ouabain-sensitive Na+-efflux, but other biogenic amines were less effective (noradrenaline and dopamine) or ineffective (histamine and serotonin). The increase of Na+-efflux induced by 1 microM adrenaline was blocked by 3 microM propranolol, but not by 3 microM phenoxybenzamine. The properties of the facilitatory action of adrenaline on the ouabain-sensitive Na+-efflux suggest that beta-adrenoceptors have an important role in modulating the Na+-K+ pump activity in the skeletal muscle membrane. The protein complex localized in excitable membranes, namely the Na+-K+ ATPase-beta-adrenoceptor complex, may be the functional unit which operates the membrane machinery driving the Na+-K+ pump.

Animals↗
PubMed1985

Histamine is an antagonist of the acetylcholine receptor at the frog endplate.

The effects of histamine on the acetylcholine (ACh) receptor-channel complex were examined by means of voltage-clamp at the frog endplate. ACh was ionophoretically applied to the endplate. Histamine was added to the perfusate. Histamine (100 nM - 1 mM) reversibly depressed the peak amplitude of the ACh-induced inward current in a dose-dependent manner. The double reciprocal plot of the dose-response relationship between the peak ACh current and the amount of ACh applied suggested that histamine (100 microM) depressed the ACh-induced current in a competitive manner. Histamine prevented the specific ACh binding site within the receptor-channel complex from binding erabutoxin, a sea-snake venom, which binds irreversibly to the specific ACh binding site. Histamine had no detectable effects on the equilibrium potential of the endplate current but shortened the half-decay time of the endplate current in a voltage-dependent manner. It was therefore concluded that histamine blocks not only the specific ACh binding site but also interacts with the ACh-channel site. The present experiments strongly suggest that histamine can act as an antagonist to modulate nicotinic cholinergic transmission.

Acetylcholine↗
PubMed1985

The mechanism of the inhibitory action of adrenaline on transmitter release in bullfrog sympathetic ganglia: independence of cyclic AMP and calcium ions.

The effects of adrenaline and dibutyryl adenosine 3':5' - cyclic monophosphate (db cyclic AMP) on nicotinic transmission in bullfrog sympathetic ganglia were compared by use of an intracellular recording technique. The evoked release of transmitter, acetylcholine (ACh), was decreased in the presence of adrenaline (10-100 microM), while the postsynaptic sensitivity to ACh was unchanged (10 microM adrenaline) or slightly reduced (100 microM). Transmitter release was similarly inhibited by dopamine (10 microM), but not by isoprenaline (10 microM). The inhibitory action of adrenaline on transmitter release was blocked by phenoxybenzamine but not by propranolol. The inhibition of transmitter release was independent of the external calcium concentration. The evoked release of transmitter and the electrical properties of the postsynaptic membrane were unchanged during exposure to db cyclic AMP (1-4 mM), while the postsynaptic sensitivity to ACh was slightly but significantly depressed. The spontaneous release of transmitter in a high K+ (10 mM) solution was decreased in the presence of adrenaline (100-300 microM), but unchanged with db cyclic AMP (4 mM). In contrast to the effects during exposure, both the evoked and spontaneous release of transmitter were enhanced after the removal of adrenaline or db cyclic AMP. Neither adrenaline (100 microM) nor db cyclic AMP (4 mM) affected the presynaptic spike and synaptic delay. It is concluded that adrenaline mainly inhibits the release of ACh from the presynaptic terminals through its alpha-action, while db cyclic AMP reduces slightly the postsynaptic sensitivity to ACh and that both agents facilitate transmitter release when they are removed from the presynaptic terminals. It is further suggested that the inhibitory action of adrenaline is independent of endogenous cyclic AMP and calcium ions.

Acetylcholine↗
PubMed1985

Effect of adenosine triphosphate on the sensitivity of the nicotinic acetylcholine-receptor in the bullfrog sympathetic ganglion cell.

The effects of adenosine triphosphate (ATP) and related compounds on the sensitivity of the nicotinic acetylcholine (ACh)-receptor of bullfrog sympathetic ganglion cells were analysed electro-physiologically. ATP in concentrations between 0.05 and 2 mM increased the amplitudes of the potentials and currents induced by ACh, and carbachol-induced currents. Compared with ATP, ADP was less potent in producing augmentation of the carbachol-induced current by one order of magnitude. AMP, cyclic AMP and adenosine had no appreciable effect. Analysis of this ATP effect, based on Michaelis-Menten type kinetics, revealed that ATP increased the maximum response (Vmax) of the dose-response curve of ACh currents without an appreciable effect on the affinity (Km) of ACh for its receptor. It is suggested that ATP increased the receptor sensitivity by acting on an allosteric site of the nicotinic ACh receptor-ionic channel complex which, thus, may be linked to an ATP receptor, probably of the P2-receptor type (Burnstock, 1981).

Acetylcholine↗
PubMed1985

Potential dependency of the electrogenic Na+-pump current in bullfrog atrial muscles.

Experiments were designed to evaluate the concept that the activity of the electrogenic Na+-pump is dependent on the transmembrane potential. Cardiac muscle preparations were used because the electrogenic Na+-pump current can be recorded at different potentials with the voltage clamp method in this preparation. Electrogenic Na+-pump current was identified as the membrane current which was abolished by ouabain (5 microM) and induced by the addition of K+ or an alkali metal cation, such as Rb+, Cs+, or Li+, to the extracellular K+-free solution. Alkali metal cations other than K+ were used to eliminate the possibility that a passive membrane K+ current might be altered by changes in the K+ concentration in the vicinity of the membrane due to activation of the Na+-pump. It was concluded that the activity of the electrogenic Na+-pump current is dependent on the membrane potential.

Animals↗
PubMed1984

Histamine as an endogenous antagonist of nicotinic ACh-receptor.

The mechanism of an inhibitory effect of histamine on the sensitivity of frog skeletal muscle endplate was analyzed by studying the dose-response relation between the quantity of ACh applied iontophoretically and the ACh-induced postsynaptic current (ACh current), and also the interaction between histamine and erabutoxin-b (ETX-b). The results obtained show that histamine, like curare, decreased the sensitivity of ACh-receptor in a competitive manner.

Animals↗
PubMed1984

Actions of ATP on the soma of bullfrog primary afferent neurons and its modulating action on the GABA-induced response.

Adenosine 5'-triphosphate (ATP) produced a long-lasting depolarization in bullfrog spinal ganglion cells. Since the ATP-induced slow depolarization was associated with an increase in membrane resistance and a reverse in polarity (about--90 mV) which was most likely brought about by an inactivation of membrane potassium conductance. In some cells, a rapid and transient depolarization followed by the long-lasting depolarization was produced by ATP and it was markedly reduced in sodium-free solution. ATP reversibly augmented the GABA-induced depolarization which was caused by ionophoresis of GABA. These observations were confirmed using a voltage clamp method. Dose-response analysis of the action of ATP on the GABA-induced response suggests that the facilitatory action of ATP on the GABA response is effected on the GABA receptor channel complexes without changing the GABA affinity.

Adenosine Triphosphate↗
PubMed1984

Neuropeptides facilitate the desensitization of nicotinic acetylcholine-receptor in frog skeletal muscle endplate.

Substance P and luteinizing hormone-releasing hormone (LHRH), neurotransmitter candidates for peptidergic neurotransmission in peripheral autonomic ganglia, facilitated the desensitization of nicotinic acetylcholine (ACh)-receptor at the skeletal muscle endplate. In the presence of these peptides, the desensitization proceeded with a biphasic time course, i.e. fast and then slow components of desensitization. We suggest that neuropeptides such as substance P and LHRH may regulate the sensitivity of nicotinic ACh-receptors by modulating the process of desensitization.

Acetylcholine↗
PubMed1984

Slow excitatory post-synaptic currents in bull-frog sympathetic neurones.

Electrogenesis of the slow excitatory post-synaptic current (slow e.p.s.c.) was analysed with voltage-clamp methods in curarized sympathetic ganglion cells of bull-frogs. Three types of slow e.p.s.c. were observed from B neurones of sympathetic ganglia. The type I slow e.p.s.c. was associated with a decrease in membrane conductance, was depressed by membrane hyperpolarization and nullified at -60 to -70 mV. It was observed in 65% of the sympathetic neurones studied. The type II slow e.p.s.c. was associated with an increase in membrane conductance, was depressed by membrane depolarization and nullified at around +5 mV. It was observed in 14% of the neurones studied. A third type of slow e.p.s.c. was recorded from 21% of the sympathetic neurones in this study. This slow e.p.s.c. was a mixed type having characteristics of both type I and type II slow e.p.s.c.s. Activation of muscarinic cholinergic receptors by application of acetylcholine (ACh) also produced two types of inward currents. The nature of each type of muscarinic slow ACh current was similar to that of each type of slow e.p.s.c. The time course of the falling phase of type I and type II slow e.p.s.c.s was dependent on the membrane potential. The type I slow e.p.s.c. was primarily dependent on extracellular K+ and appeared to be produced by a suppression of the M-current (Brown & Adams, 1980). The type II slow e.p.s.c. was due to an increased conductance, probably to Na+, and other cations.

Acetylcholine↗
PubMed1984

Modulation of receptor sensitivity and action potentials by transmitters in vertebrate neurones.

The nicotinic cholinergic transmission causing generation of the fast EPSP in bullfrog sympathetic ganglia is modulated by the action of transmitters or hormones other than ACh. In general, a synaptic transmission appears to be modulated in a variety of ways by the action of many kinds of transmitters or hormones in the vertebrate neural system. There are at least four different types of modulatory actions of these endogenous substances on a synaptic transmission; namely, 1) modulation of the amount of the transmitter released from presynaptic neurones, 2) modulation of the sensitivity of the receptors of postsynaptic neurones, 3) modulation of the resting membrane potential or conductance of postsynaptic neurones, 3) modulation of the resting membrane potential or conductance of postsynaptic neurones, and 4) modulation of the configuration of the action potential of postsynaptic neurones. In the present review, the experimental evidence supporting the modulatory actions of endogenous substances on the receptor sensitivity and the action potential of postsynaptic neurones was reviewed. The mechanisms underlying these two types of modulatory actions were also briefly discussed.

Acetylcholine↗
PubMed1983

Modulation of action potential during the late slow excitatory postsynaptic potential in bullfrog sympathetic ganglia.

The spike peak and after-hyperpolarization of the action potential of bullfrog sympathetic ganglion cells were depressed during the late slow excitatory postsynaptic potential (EPSP). These changes in the action potential were mimicked by luteinizing hormone-releasing hormone (LH-RH), a neurotransmitter candidate for the late slow EPSP. LH-RH (5 microM) suppressed the voltage-dependent K+ currents, both the delayed rectifier K+ current (IK1) and the M current (IK2). It is suggested that the depression of the after-hyperpolarization of the action potential during the late slow EPSP may be due to suppression of IK1 and IK2.

Action Potentials↗