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Biomedical subjects

K Kuba

Publications and source records attributed to K Kuba.

At least 127 records · Page 7Linked to original sources
PubMed1976

Rhythmic hyperpolarizations and depolarization of sympathetic ganglion cells induced by caffeine.

Superfusion of the isolated sympathetic ganglion of the bullfrog with a caffeine-containing (1-6 mM) solution caused in many cells an initial slow hyperpolarization which was followed by a subliminal depolarization interruped by rhythmic hyperpolarizations. A hyperpolarization, similar to one of the rhythmic hyperpolarizations, could be triggered by an action potential in the presence of caffeine. The action potential itself was not markedly affected by caffeine except for its afterhyperpolarization which was prolonged. All these caffeine-induced hyperpolarizations were associated with a marked reduction of the membrane resistance, their amplitude was increased in a K+-free solution and decreased in a high-K+ solution, and their polarity was reversed at the same level at which the afterhyperpolarization was also inverted. This reversal level was not altered by omission of Na+ or C1- from the external medium. These hyperpolarizations were reversibly abolished by depletion of external Ca2+ or replacement of external Ca2+ by Mg2+. Excess of external Ca2+ caused a shortening of the interval between rhythmic hyperpolarizations. Furthermore, iontophoretic injection of EDTA into the cytoplasm markedly depressed the initial caffeine hyperpolarizatin and abolished both the rhythmic and evoked caffeine hyperpolarizations. The caffeine-induced depolarization was not affected by omission of external Cl-. It was decreased in a Na+-free medium, but completely eliminated by omission of both Na+ and Ca2+ from the external medium. Tetrodotoxin did not impair the production of the initial and the rhythmic hyperpolarizations. A strong depolarizing pulse could evoke a typical hyperpolarizing response in the presence of this compound. Dibutyryl cyclic AMP, d-tubocurarine, atropine, and phenoxybenzamine were without effect on the caffeine-induced hyperpolarizations and depolarization. It was concluded that each caffeine-induced hyperpolarization is the result of an increased K+ permeability, which is probably caused by a rise in the internal Ca2+ concentration. It was also concluded that the caffeine-induced depolarization is due to an increased membrane permeability to Ca2+ and Na+.

Animals↗
PubMed1976

Novel action of a piperazine derivative on the end-plate of the frog.

The effects of a piperazine derivative, trimetazidine (1-(2, 3, 4-trimethoxybenzyl) piperazine dihydrochloride) on the frog end-plate membrane were studied. Action and resting membrane potentials and the input resistance of muscle fibers were not affected by trimetazidine (82-165 muM). Under these conditions, the frequency of the miniature endplate potentials was unchanged while its amplitude was slightly decreased. The amplitude of acetylcholine (ACh) potentials were markedly and reversibly decreased after application of trimetazine (82-165 muM). The dose response curve of the end-plate membrane to ACh showed a non-competitive type of blockade. Trimetazidine (165 muM) not only decreased the amplitude of the end-plate currents (EPC) recorded from the glycerinated muscles using a voltage clamp technique, but also drastically shortened its time course. Under these conditions, the falling phase of the EPC became completely voltage insensitive. The equilibrium potential for the EPC slightly shifted to a more negative value in the presence of trimetazine (165 muM). Coefficient of variation of EPC was increased by Trimetazidine (165 mum), indicating a decrease in the quantal content of the EPC. The rate of desensitization of the end-plate to ACh was facilitated and the rate of decrease in EPC amplitude during tetanic stimulation became voltage sensitive by the action of trimetazidine (133 muM). It is concluded that trimetazidine mainly acts on the postsynaptic membrane with a weak presynaptic action. The agent seems to block a step subsequent to the interaction of ACh with its receptor, which presumably involves changes in the ion conductance of the membrane and is responsible for the voltage sensitivity of the response.

Acetylcholine↗
PubMed1976

Analysis of the slow excitatory postsynaptic potential in bullfrog sympathetic ganglion cells.

The ionic mechanism of the slow excitatory postsynaptic potential (slow EPSP), i.e. the muscarinic action of acetylcholine (ACh), was studied either by stimulating preganglionic nerves or by applying ACh in curarized sympathetic ganglion cells of bullfrogs. There are three different types of cells characterized by the effects of membrane hyperpoliarization on the amplitude of slow EPSP. One group of cells showed an increase in amplitude (type 1 cell) and, in two other groups of cells, it remained unchanged (type 2 cell) or decreased (type 3 cell), when the membrane was hyperpolarized. Under the muscarinic effects of ACh, the slope membrane conductance was increased (type 1 cell), unchanged (type 2 cell) or decreased (type 3 cell) at 10-20 mV hyperpolarized levels, while it was unchanged (type 1 cell) or decreased (types 2 and 3 cells) at resting and depolarized levels. In all cells, the slow ACh potential, corresponding to the slow EPSP, was almost completely suppressed in a high K+, Ca2+-free, Na+-free solution. These results suggest that the slow EPSP is generated by increases in Na+ and Ca2+ conductance and also by a simultaneous decrease in the K+ conductance.

Acetylcholine↗
PubMed1976

The muscarinic effects of acetylcholine on the action potential of bullfrog sympathetic ganglion cells.

The direct effects of acetylcholine (ACh) on Na+- or Ca2+-dependent action potentials of curarized sympathetic ganglion cells in bullfrogs were investigated under a condition where membrane depolarization caused by the muscarinic action of ACh was nullified by means of a hyperpolarizing current. ACh decreased the after-hyperpolarization of Na+-action potentials in Ringer's solution, and increased the after-depolarization of Ca2+-action potentials in the isotonic Ca2+ solution. In both solutions, the maximum rates of rise of the spikes were decreased and the slope membrane resistance at the original resting level was increased. The effects of ACh were abolished by atropine. On the other hand, ACh showed no significant effects on action potentials of bullfrog spinal ganglion cells which possessed no synapses. These results suggest that the ion conductance channels for generation of action potentials of sympathetic ganglion cells are under the direct control of transmitters, such as ACh.

Acetylcholine↗
PubMed1976

Enzymatic determinations of cholesterol in high-density-lipoprotein fractions prepared by a precipitation technique.

An enzymatic method for cholesterol in serum [Clin. Chem. 20, 470 (1974)] was initially found to be unsatisfactory for measuring cholesterol in high-density-lipoprotein fractions prepared by precipitation with Mn2+. A fine precipitate formed in the cuvette and cholesterol values were falsely increased. We describe a simple, convenient method for circumventing these problems. An ethylenediaminetetraacetate solution is used to reconstitute the enzymatic reagent. Cholesterol values by this procedure correlated with those obtained by the Lipid Research Clinic's procedure for the same lipoprotein fraction preparations (regression slope, .998; Y-intercept, 8.9 mg/liter; correlation coefficient, .984; standard error of the estimate, 16.8 mg/liter). Precision of the assay, including the precipitation step, was calculated. The SDwithin day was 9.7 mg/liter and SDoverall was 23.7 mg/liter. Results for total cholesterol with the modified reagent were linearly related to concentrations exceeding 4 g/liter, thereby permitting determination of high-density-lipoproteins and total cholesterol in a single run.

Chemical Precipitation↗
PubMed1976

Plasma high-density lipoprotein cholesterol concentrations determined after removal of other lipoproteins by heparin/manganese precipitation or by ultracentrifugation.

The widely used heparin/MnCl2 precipitation procedure for determination of plasma high-density lipoprotein cholesterol has been re-examined in light of recent reports that isolated preparations of the lipoprotein are only partly precipitated under the test conditions. In the present study, the procedure as applied to plasma tolerated rather wide variations in heparin and MnCl2 concentrations without significant effects on the assayed values in several plasma pools tested. The procedure was further tested on 129 individual samples by comparison with an ultracentrifugal method in which high-density lipoprotein-cholesterol is assumed to be represented by the cholesterol content of the plasma fraction of relative (to water) density greater than 1.063. Our results indicate that high-density lipoprotein is not precipitated under the test conditions when applied to unfractionated plasma.

Cholesterol↗
PubMed1973

Diisopropylfluorophosphate: suppression of ionic conductance of the cholinergic receptor.

When frog sartorius muscles were exposed to diisopropylfluorophosphate, the amplitude and half-decay time of the end-plate current decreased; the half-decay time became almost potential-independent and the equilibrium potential for the end-plate current was more negative than during control conditions. When the excess reagent was removed by washing so that only the phosphorylated acetylcholinesterase remained, the amplitude of the end-plate current was restored, while its half-decay time was markedly increased. These findings reveal that this organophosphate significantly affects the receptor-ionic conductance modulator complex in addition to its well-known anticholinesterase activity.

Animals↗
PubMed1971

Effect of prostigmine on the time course of the end-plate potential in the rat diaphragm.

1. End-plate potentials (e.p.p.s) were evoked by applying brief depolarizing pulses to motor nerve endings in a phrenic nerve-diaphragm preparation paralysed by tetrodotoxin (TTX). Without prostigmine, the time to decay from the summit of the e.p.p. to half amplitude (the half-decay time) was roughly constant (2-4 msec) when the amplitude was increased by increasing stimulus intensity or duration.2. In the presence of prostigmine (5 x 10(-7)-2 x 10(-5) g/ml.), the falling phase of the e.p.p. was different in time course depending on the amplitude. The half-decay time had, very roughly, an exponential dependence on amplitude. The relationship was not affected by increasing the TTX or the prostigmine concentration, but D-tubocurarine (10(-6) g/ml.) made the relationship less steep.3. Hyperpolarizing current pulses, applied after the depolarizing current pulse which produced the e.p.p., had no effect on the time course of the e.p.p. No facilitating effect of repetitive stimulation was observed without prostigmine up to a frequency of 40 c/s, but there was a strong effect of repetitive stimulation in increasing the amplitude and duration of the e.p.p. in the presence of prostigmine. During stimulation, the endplate was continuously depolarized by 10-20 mV, and its recovery was very slow, the half-decay time being about 3 sec.4. The half-decay time of the acetylcholine potentials produced by iontophoretically applied acetylcholine was almost independent of the amplitude, with or without prostigmine, although it increased the amplitude of the potential and prolonged the falling phase.5. Possible mechanisms for the alteration of the falling phase of the e.p.p. were discussed. It is speculated that, in the presence of prostigmine, a process which is involved in a conductance increase of the post-synaptic membrane, after acetylcholine has combined with the receptor molecules, is the main factor determining the falling phase of the e.p.p.

Acetylcholine↗
PubMed1971

Noradrenaline action on nerve terminal in the rat diaphragm.

1. The mechanism by which noradrenaline increases the release of transmitter from the nerve terminal was investigated in the rat diaphragm.2. Increase of the frequency of the miniature end-plate potential (m.e.p.p.) was exponential when plotted against the intensity of a constant current which depolarized the nerve terminal. Noradrenaline (5 x 10(-6) g/ml.) did not change the slope of the curve showing the relationship between the logarithm of the frequency of m.e.p.p.s and the depolarizing current (m.e.p.p.-current relationship), but simply shifted the curve along the axis of the current towards weaker intensities.3. End-plate potentials (e.p.p.s) were evoked by passing a brief depolarizing pulse to the nerve terminal in the presence of tetrodotoxin (1 x 10(-7) g/ml.). A sigmoidal relationship was obtained between the amplitude of e.p.p. and the intensity of the current pulse (e.p.p.-current intensity relationship). Noradrenaline (5 x 10(-6) g/ml.) shifted the e.p.p.-current intensity relationship along the axis of the current intensity to smaller values, without any change in the maximum amplitude of e.p.p.s.4. The frequency of m.e.p.p. was increased, as the [Ca](0) was raised from 0.01 to 7.5 mM. An increase in [Ca](0) beyond the normal concentration (2.5 mM) had no remarkable effect on the action of noradrenaline. However, when [Ca](0) was reduced, the action of noradrenaline became weaker.5. A kinetic model in which the transmitter release is modified by the binding of Ca with a specific site in the nerve terminal may explain the results. According to this model, noradrenaline did not change the dissociation constant of the reaction between Ca and the specific site (X), but increased the rate constant of the Ca complex (CaX) for releasing acetylcholine.6. The action of noradrenaline was potentiated when [Na](0) was reduced, and suppressed when [Mg](0) was increased. The results may be summarized: that noradrenaline augments the probability of release of transmitter quanta from the resting nerve terminals and that this action can be intensified by first raising the probability of release by some other means. Depolarization of the nerve terminals by current, increase of the external Ca concentration, decrease of Na and decrease of Mg are all effective in promoting the action of noradrenaline.

Acetylcholine↗
PubMed1970

Effects of catecholamines on the neuromuscular junction in the rat diaphragm.

1. The effects of noradrenaline, adrenaline and isoprenaline on neuromuscular transmission in the rat diaphragm and the influence of adrenergic blocking agents on these actions were investigated.2. The resting membrane potential of the muscle fibre was increased by adrenaline (5 x 10(-6)-10(-5) g/ml.) and isoprenaline (5 x 10(-6) g/ml.) up to 3-4 mV, but noradrenaline (5 x 10(-6)-10(-5) g/ml.) had little effect.3. The amplitude and the half-decay time of the end-plate potential (e.p.p.) were increased by noradrenaline (1 x 10(-6) g/ml.), adrenaline (1 x 10(-7)-10(-5) g/ml.) and isoprenaline (1-5 x 10(-6) g/ml.). The potentiation of the amplitude of the e.p.p. was greater with noradrenaline than with adrenaline and isoprenaline.4. Noradrenaline (5 x 10(-6) g/ml.) increased the frequency of miniature end-plate potentials (m.e.p.p.), but not their amplitude. However, isoprenaline (5 x 10(-6) g/ml.) increased the amplitude of m.e.p.p.s without change in frequency. Adrenaline (5 x 10(-6) g/ml.) increased both frequency and amplitude of m.e.p.p.s.5. Adrenaline (5 x 10(-6) g/ml.) and isoprenaline (5 x 10(-6) g/ml.) increased the input resistance of the muscle membrane. The effect was blocked by the beta-blocker, pronethalol (2 x 10(-6) g/ml.), but not by the alpha-blocker, phentolamine (2 x 10(-6) g/ml.). Noradrenaline did not change the input resistance of the muscle fibre.6. Noradrenaline (5 x 10(-6) g/ml.) and adrenaline (5 x 10(-6) g/ml.) augmented the extracellularly recorded end-plate current (e.p.c.), but they had no effect on the half duration, nor on the action current (a.c.) of the nerve terminal, nor on the synaptic delay. Isoprenaline (5 x 10(-6) g/ml.) had no effect on any of these parameters. The actions of noradrenaline and adrenaline on e.p.c. were abolished by phentolamine (2 x 10(-6) g/ml.), but not by pronethalol (2 x 10(-6) g/ml.).7. Adrenaline (5 x 10(-6) g/ml.) and isoprenaline (5 x 10(-6) g/ml.) enhanced the amplitude of the acetylcholine potential elicited by iontophoretic application of acetylcholine. No such effect was produced by noradrenaline (5 x 10(-6) g/ml.).8. It was concluded that noradrenaline acts on the nerve ending increasing the release of transmitter, and that isoprenaline acts on the post-synaptic membrane enhancing the input resistance, while adrenaline has both presynaptic and post-synaptic actions. The effect on the nerve ending is concerned with the alpha-action, whereas that on post-synaptic membrane with beta-action of the catecholamines.

Acetylcholine↗