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Biomedical subjects

K Kusano

Publications and source records attributed to K Kusano.

At least 109 records · Page 6Linked to original sources
PubMed1983

Calcium binding sites of hamster parasympathetic neurons.

Sites of Ca localization in hamster submandibular ganglion cells have been studied by electron microscopy using the technique of Oschman et al. [11]. Electron-dense deposits, which we assume to contain Ca, are found: (i) on axonal plasma membranes; (ii) on the plasma membranes of neuron soma and its processes; (iii) on the membrane of clear vesicles in the nerve terminal; and (iv) in the matrix of mitochondria. Intracellularly injected Ca accumulates in the mitochondria. Caffeine reduces the electron-dense deposits seen in mitochondria. Caffeine induces a swelling of Golgi apparatus when applied with CaCl2, but this swelling is not observed without CaCl2. These results are discussed in the light of Ca-activated K-conductance increases, which induce 4 types of membrane potential changes [18, 19].

Animals↗
PubMed1983

Rhythmic membrane potential changes in hamster parasympathetic neurons.

Two types of rhythmic membrane potentials in hamster submandibular neurons: (i) slow oscillations of membrane potential (SOMP); and (ii) spontaneous or caffeine-induced rhythmic hyperpolarizing potentials (C-HPs), have been analyzed. SOMPs occurred spontaneously, roughly in sinusoidal forms, between the subthreshold range and the potassium equilibrium potential (EK, approximately -85 mV). The average amplitude of SOMPs from crest to trough was 12 mV with an average crest to crest interval of 6 min. The largest amplitude of SOMPs was seen when their median membrane potentials were between -65 and -70 mV; values outside this range attenuated the amplitude of SOMPs. SOMPs were hardly discernible at or near EK. The membrane resistance was, in general, higher at the crest than at the trough. In eserine-treated preparations, SOMPs of varying durations following postsynaptic potentials were triggered by preganglionic repetitive stimulation. Reduction of extracellular K+ concentration increased the amplitude of SOMP without changing its frequency. This effect was noted at times before K+-free induced membrane depolarization occurred. The amplitude of the SOMP decreased in Ca2+-free saline with concomitant depolarization; conversely, in saline in which the Ca2+ concentration was doubled the membrane potential (Em) was found to be again stable near the EK level. A transient hyperpolarization occurred following intracellular Ca2+ injection when the Em of the preinjected state was between -45 and -60 mV. Among K+-conductance (GK) blockers (TEA, 3- and 4-aminopyridine, Cs+ and Ba2+) examined, only Ba2+ at 5 mM reduced both amplitude and frequency of C-HPs significantly. All Ca2+-conductance (GCa) blockers (Co2+ and Mn2+ at 5 mM, Cd2+ and La3+ at 1 mM, and D-600 at 0.4 mg/ml) prevented synaptic transmission and abolished spike-induced late hyperpolarizing afterpotential. C-HPs were nearly abolished by these agents in 4 mM Ca2+-containing saline. Mitochondrial inhibitors (DNP, CCCP, KCN, NaN3) in a concentration range between 10(-4) M and 10(-5) M, hyperpolarized the membrane before depolarizing and abolishing C-HPs. However, the plasma membrane Na+-pump inhibitor ouabain, at concentrations up to 5 X 10(-4) M, did not affect C-HPs during 1 h perfusion in the majority of neurons; no membrane hyperpolarization was induced, although a gradual depolarization did occur. Both ruthenium red (5 mM) and quinine (5 X 10(-4) M) abolished C-HPs. It is assumed that the two above types of membrane potential changes are generated by the Ca2+-activated GK increase, which, in turn, is under the control of mitochondrial Ca2+ regulatory activity.

Animals↗
PubMed1982

Cholinergic and catecholaminergic receptors in the Xenopus oocyte membrane.

1. Neurotransmitter-receptors in the membrane of Xenopus oocytes have been studied using electrophysiological techniques. Neurotransmitters and related agents were applied while recording either membrane potential or membrane current. The majority of ovarian oocytes used were at stages IV and V.2. Three types of oocytes were examined: inner ovarian epithelium covered (e.c.) oocytes; epithelium manually removed (e.r.) oocytes; and collagenase treated (c.t.) ooctyes.3. Ovarian oocytes are sensitive to some cholinergic and catecholaminergic agents. Responses to serotonin were seldom observed and when present were much weaker than responses to other agents. No responses were observed to the amino acids: aspartate, glutamate, gamma-aminobutyric acid, and glycine; or to octopamine and histamine.4. Acetylcholine (ACh) usually depolarized the membrane, in a dose-dependent manner, with threshold concentrations as low as 10(-9)m. The ACh-potential was due to an increase in Cl permeability and had a reversal potential around - 19 mV. The intracellular Cl ion activity, measured with a Cl-ion sensitive micro-electrode, was about 65 mm and the estimated Cl-ion equilibrium potential, E(Cl), agreed with the reversal potential of the ACh-potential.5. Curare (10(-4)m), tetrodotoxin (10(-6)m), or alpha-bungarotoxin (10(-6) g/ml.) did not block the response to 10(-6)m-ACh; whereas atropine (10(-7)m) blocked it. No response to nicotinic agents (e.g. nicotine, 1,1-dimethyl-4-phenylpiperazinium) was observed. These results suggest that the ACh receptors in the oocyte membrane are muscarinic in nature.6. The apparent latency of the ACh potential, examined by ionophoretic application of ACh to e.r. oocytes and c.t. oocytes, ranged from 0.5 sec to over 20 sec. Intracellular injection of ACh was without effect.7. Responses to catecholamines were observed mostly in e.c. oocytes; while in e.r. and c.t. oocytes they were rare and of very small amplitudes.8. The usual response to both dopamine and (-)-epinephrine was a transient hyperpolarization manifested by an initial increase in K-permeability followed by a decrease. The latency of these responses ranged from 10 sec to over 30 sec and their reversal potential was nearly - 100 mV, which coincided with E(K).9. Oocytes responded to the beta-adrenergic receptor agonist, isoproterenol, as well as (-)-epinephrine. Pre-treatment with the beta-adrenergic receptor blocker, propranolol, abolished the response to both (-)-epinephrine and (-)-isoproterenol. The dopamine potential was also reduced considerably. Both the alpha-adrenergic receptor agonist, phenylephrine, and the alpha-adrenergic receptor blocker, phentolamine, were without effect.10. Maturation of the oocytes, induced in vivo by gonadotropin or in vitro by progesterone, led to loss of responsiveness to both cholinergic and catecholaminergic agents.

Acetylcholine↗
PubMed1980

Studies on anticoccidial agents. 13. Synthesis and anticoccidial activity of nitropyridine-2- and -3-sulfonamides and derivatives.

Eight nitropyridinesulfonamides and pyridinesulfonamide N-oxides as their bioisosteres were prepared and evaluated for anticoccidial activity. Of these compounds, 2-, 4- and 5-nitropyridine-3-sulfonamides and pyridine-2- and -3-sulfonamide N-oxides were found to be active against Eimeria tenella. Thus, the relative positions, ortho or meta, of the substituents in nitropyridine-3-sulfonamides and pyridinesulfonamide N-oxides are important for anticoccidial activity. N-Substituted analogues of 5-nitropyridine-3-sulfonamide were also prepared and optimal anticoccidial activity was attained with the sulfonamide and its lower N-alkyl derivatives. The mode of action of 5-nitropyridine-3-sulfonamide was examined and found to be active in the sporozoite and the first schizogony stages.

Animals↗
PubMed1978

Hyperpolarizing potentials induced by Ca-mediated K-conductance increase in hamster submandibular ganglion cells.

The mechanisms of three types of hyperpolarizing electrogenesis in hamster submandibular ganglion cells were analyzed with intracellular microelectrodes. These included (1) spike-induced hyperpolarizing afterpotential (S-HAP), (2) spontaneous transient hyperpolarizing potential (HP), and (3) the hyperpolarizing (H) phase of postsynaptic potential (PSP). Most of these hyperpolarizing potentials were due to conductance increases and reversed polarity at membrane potential (Em) between -70 and -85 mV, which was close to the K-equilibrium potential. The average resting potential of ganglion cells was -53 mV. Action potential overshoot increased slightly in high [Ca2+]0 and decreased in low [Ca2+]0. In most neurons action potentials were completely suppressed by 10(-7)-M tetrodotoxin (TTX). The S-HAP has an initial component due to delayed rectification and a late component. The late component is enhanced by increasing [Ca2+]0, or by applying Ca-ionophore (A23187), TEA, caffeine, or dibutyryl cyclic (DBc-) AMP; it is suppressed by decreasing [Ca2+]0, or by applying Mn2+. Perfusion with Cl--free saline reduced membrane potential slightly but did not modify the S-HAP. Depolarizing pulses also induced hyperpolarizing afterpotential (D-HAP), similar to the S-HAP. Spontaneous transient HPs occurred in some neurons at irregular intervals. HPs were insensitive to TTX but were suppressed by Mn2+. Caffeine induced low frequency rhythmic HPs in many neurons, often alternating with periods of repetitive spiking. The PSP was a monophasic depolarizing (D-) potential in some neurons, but in others the D-phase was followed by a small H-phase. Perfusion with A23187, caffeine or DBc-AMP increased the H-phase of the PSP. Perfusion with K+-free saline or treatment with 10(-5)M ouabain did not abolish the H-phase of PSPs. These membrane potential-dependent phenomena appear to be induced mainly by Ca-mediated K-conductance increases. This mechanism contributes to the regulation of low-frequency repetitive firing in submandibular ganglion cells.

Action Potentials↗
PubMed1978

Studies on anticoccidial agents. 12. Synthesis and anticoccidial activity of methyl-2(6)-nitro- and -3(5)-nitropyridinecarboxamides.

A number of methyl-2- and 3-nitropyridinecarboxamides have been synthesized. It has been established that the presence of at least one hydrogen atom, adjacent to the NO2 function, is important for anticoccidial activity and introduction of a methyl group to the adjacent position of the CONH2 function sometimes confers enhanced activity. Among the compounds herein, 5- and 6-methyl-2-nitropyridine-4-carboxamides possess optimal anticoccidial activity, being as potent as the parent compound.

Coccidiostats↗
PubMed1975

Depression and recovery of transmission at the squid giant synapse.

1. The process of synaptic depression and recovery were studied in the squid (Loligo pealii) giant synapse with intracellular recording and stimulating electrodes in the prescence of tetrodotoxin (10-minus 7 M). 2. When the synapse was stimulated at 50 Hz, depression occurred rapidly. Recovery after the tetanus was a first-order process with an average recovery time constant of 4-9 sec. The rate of recovery was independent of the amplitude of the post-synaptic potential (p.s.p.) or the degree of depression. 3. For the first five to seven p.s.p.s in the train there was a linear relationship between depression and the total amount of transmitter previously released. This may indicate that depression in this preparation was caused by the depletion of the presynaptic store of transmitter (S). 4. Assuming that this interpretation was correct, we could show that recovery from depression during the tetanus (i.e. 'mobilization') proceeded about 10 times faster than after the end of the tetanus. 5. When the amplitude of the p.s.p. was varied by changing the bathing calcium concentration, [Ca], the degree of depression was correlated to the amplitude of the p.s.p. 6. When the amplitude of the p.s.p. was increased by increasing pre-synaptic depolarization, synaptic depression was found to increase as well. However, synaptic depression increased less than the amplitude of the p.s.p., the relationship between these two measures being non-linear. 7. This finding is interpreted to indicate that the transmitter stores, S, are closely related to the area of the presynaptic membrane which is sufficiently depolarized to release transmitter.

Action Potentials↗
PubMed1973

Potentiation by endotoxin of responses associated with increases in calcium conductance.

Bacterial endotoxin at concentrations of 0.03 mug/ml enhanced the following responses, each of which reflects calcium influx: (1) contraction of spiral intestine retractor muscle of dogfish; (2) amplitude of postsynaptic potential of squid giant synapse as a function of presynaptic depolarization; (3) membrane responses of deep abdominal extensor muscle of crayfish, stimulated intracellularly; and (4) slow transient (calcium) current in trabeculae of frog atrium under voltage clamp. Corticosteroid antagonized the endotoxin effect on the smooth muscle, not on the frog atrial current. One mechanism of action of endotoxin may be to increase transmembrane calcium currents.

Action Potentials↗