PubMed Health⌕ Search

Biomedical subjects

Y Kidokoro

Publications and source records attributed to Y Kidokoro.

At least 73 records · Page 4Linked to original sources
PubMed1983

Metabolism of acetylcholine receptors on embryonic amphibian muscle.

The functional properties of acetylcholine receptors are altered during the development of Xenopus myotomal muscle. A similar change also occurs in dissociated cell cultures of embryonic myotomal muscle. Metabolism of acetylcholine receptors was examined in order to ascertain whether the turnover rate changed at a time when the functional changes were detected. Incorporation of newly synthesized receptors occurred at a constant rate over a 24-hr period. The degradation of receptors followed first order kinetics with a half-life of 52 hr. Incorporation and degradation occurred at approximately equal rates such that 1 to 1.5% of the total receptor number was replaced every hour at equilibrium. Addition of neural tube cells to muscle cell culture, which altered the functional properties of channels, had no effect on either the incorporation or the degradation rate. We conclude that the changes in the functional properties of receptors occur independent of changes in the turnover rate of receptors.

Acetylcholine↗
PubMed1982

Initial synaptic transmission at the growth cone in Xenopus nerve-muscle cultures.

The excellent visibility of cultured cells allows the early events during formation of the neuromuscular junction to be suitably studied. It has been shown in various culture systems that synaptic transmission occurs early after nerve-muscle contact. Early synaptic potentials are small in amplitude and slow in time course reflecting a low acetylcholine receptor density at the site of nerve contact. Acetylcholine receptors accumulate later at the contact region. We have examined initial synaptic transmission at the growth cone-muscle contact in Xenopus nerve-muscle cultures. The approaching growth cone was observed under a phase-contrast microscope while the membrane potential of its target muscle cell was continuously monitored by using an intracellular microelectrode. The innervating neuron was stimulated extracellularly at the cell body. No synaptic potential was evoked when the growth cone was contacting the muscle only at the tip of filopodia. However, as soon as the main portion of the growth cone contacted the muscle membrane, nerve-evoked synaptic potentials were detected after stimulation of the nerve. This immediate appearance of synaptic potentials raises the possibility that acetylcholine could be released at the growth cone even prior to contact with muscle cells. As the area of contact enlarged during the observation period the amplitude of end-plate potentials also increased. Spontaneous synaptic potentials (miniature end-plate potentials) were rarely observed in these early growth cone-muscle contacts. Although there were several inherent difficulties, quantal analysis of the end-plate potentials was attempted by using binomial statistics. This analysis suggests that nerve-evoked transmitter release at the growth cone occurs in a quantal fashion.

Acetylcholine↗
PubMed1982

Acetylcholine-induced membrane depolarization and potential fluctuations in the rat adrenal chromaffin cell.

1. The effect of acetylcholine (ACh) on the rat adrenal chromaffin cell membrane was examined in culture by using an intracellular recording technique. ACh was applied with gas pressure through a pipette which had an internal tip diameter of about 3 mum.2. Upon application of ACh the chromaffin cell membrane depolarized with superimposed potential fluctuations. Occasionally repetitive spikes were observed during the entire period of ACh application up to 30 sec. In some cells a hyperpolarization with a slow time course followed the initial depolarization.3. The depolarization was detectable with 0.1 mum-ACh; the amplitude increased with higher concentrations of ACh and saturated at 100 mum. The half-maximal concentration was approximately 10 mum.4. The amplitude of the ACh depolarization increased when the membrane was hyperpolarized by passing current through the recording electrode, and decreased upon depolarization. This technique gave an apparent reversal potential of -24+/-4 mV (mean+/-S.D., n = 6).5. When the mean amplitude of the ACh depolarizations and the variance of the potential fluctuations in a given cell were plotted, a linear relation was found. The slope was 0.23+/-0.06 mV (n = 9) at the average membrane potential level of -60 mV. With a few assumptions this value approximates the amplitude of an elementary potential change.6. Temporal characteristics of the potential fluctuations were obtained by calculating an auto-correlation function. The averaged auto-correlation function in a given cell declined exponentially with time. The mean time constant at 31 degrees C was found to be 40+/-19 msec (n = 9) at the average membrane potential level of -60 mV. With a few assumptions this value provides an estimate of the mean duration of an elementary potential change.7. The ionic mechanism of the ACh depolarization was examined by changing the ion composition of the external solution. Na, K and Ca ions appear to be the current carriers during the ACh depolarization; Cl ions do not contribute.8. Various ACh receptor agonists and antagonists were applied to determine the pharmacological properties of these ACh receptors. The receptors were found to be nicotinic.9. The nature of the ACh-induced membrane potential fluctuations is discussed.

Acetylcholine↗
PubMed1980

Chromaffin cell action potentials and their possible role in adrenaline secretion from rat adrenal medulla.

1. The role of action potentials in adrenaline secretion was investigated in the rat adrenal medulla. The effects of various treatments on adrenaline secretion from the perfused adrenal medulla were compared with the effects of similar treatments on spike frequency in dissociated adrenal chromaffin cells. 2. KCl concentrations between 10 and 20 mM increased the extracellularly recorded spike frequency of dissociated adrenal chromaffin cells. Upon perfusion by a KCl concentration of 30 mM there was an initial brief burst of spikes followed by a period of inactivity in the continued presence of 30 mM-Kcl. Tetrodotoxin (TTX, 6 microM) decreased the amplitude and frequency of the KCl evoked spikes. 3. The rate of adrenaline secretion from the isolated perfused rat adrenal gland increased as the KCl concentration was raised to 10 and up to 120 mM. Secretion which was evoked by KCl concentrations between 10 and 20 mM was partially inhibited by TTX. At KCl concentrations of 30 mM or greater evoked secretion was no longer affected by TTX. 4. CoCl2 (5 mM) blocked KCl increase of spike frequency and also blocked stimulation of adrenaline secretion by all concentrations of KCl tested. 5. Tetraethylammonium chloride (10 mM), which decreased spike frequency but greatly prolonged the spike duration, enhanced secretion induced by 15 mM-Kcl. 6. The results are consistent with the following interpretation. The TTX insensitive portion of the KCl stimulated adrenaline secretion is due to Ca influx through voltage dependent Ca channels which are open as a consequence of the steady-state level of KCl depolarization. The TTX sensitive portion of secretion is indicative of an extra increment of Ca influx during spike activity enhanced by KCl. This increment of Ca influx may occur through voltage dependent Ca channels whose activation is facilitated by the voltage changes caused during the TTX sensitive Na component of the spike and possibly through the Na channel itself. 7. Stimulation of secretion by acetylcholine (ACh) in the perfused adrenal medulla was half maximal at 15 microM and began to saturate around 50 microM. Release was partially inhibited by TTX only when the concentration of ACh was 10 microM or less. The possible role of action potentials in ACh stimulated adrenaline release is discussed.

Acetylcholine↗
PubMed1977

Cholinergic metabolism and synapse formation by a rat nerve cell line.

The PC12 clone of a rat pheochromocytoma is able to synthesize acetylcholine. The amount of acetylcholine synthesized, and the specific activity of choline O-acetyltransferase (acetyl-CoA:choline O-acetyltransferase, EC 2.3.1.6), varies as a function of the culture growth curve and is dependent on cell density. The specific activity of choline acetyltransferase is increased by nerve growth factor, growth-conditioned medium from a variety of cell types, and adenosine 3':5'-monophosphate. Finally, the PC12 cell line is able to form cholinergic synapses with a clonal cell line of skeletal muscle origin.

Acetylcholine↗
PubMed1977

Relationship of leukocyte elastase concentration to severity of emphysema in homozygous alpha1-antitrypsin-deficient persons.

In 9 alpha1-antitrypsin-deficient (PiZZ) persons 40 to 53 years of age, the relationships between the concentration of elastolytic protease of polymorphonuclear leukocyte granules and cigarette smoking, and the degree of abnormality in detailed pulmonary function tests were explored. Regardless of the statistical analytic approach used, elastase concentration was related more frequently and significantly than smoking history to the degree of abnormality observed in tests of pulmonary function. The data suggest that the severity of pulmonary dysfunction in PiZZ persons may be determined by variables other than age and cigarette smoking, including the concentration of elastolytic protease in leukocyte lysosomes.

Adult↗
PubMed1976

Action potentials in the rat chromaffin cell and effects of acetylcholine.

1. Electrophysiological properties of the rat chromaffin cell were studied using intracellular recording techniques. 2. The resting potential in the chromaffin cell was -49 +/- 6 mV (mean +/- S.D., n = 14) in standard saline containing 10 mM-Ca whereas that in Na-free saline was -63 +/- 9 mV (n = 17). At rest, the membrane has a substantial Na permeability. 3. Action potentials were evoked by passing current through the recording electrode. In standard saline the major fraction of the action potential disappeared either upon omission of external Na ions from standard saline or addition of 1 muM tetrodotoxin (TTX). We conclude that action potentials in the chromaffin cell are due mainly to an increase in the permeability of the membrane to Na ions. 4. Small but significant regenerative action potentials were observed in Na-free saline, and when Ca in Na-free saline was replaced by Ba, prolonged action potentials occurred. We conclude that action potentials in the chromaffin cell also have a Ca component. 5. Iontophoretic application of acetylcholine (ACh) produced a transient membrane depolarization in standard saline. 6. Spontaneous action potentials were recorded extracellularly by microsuction electrodes. They occurred at a rate of 0-05-0-1/sec in almost all cells. 7. When the perfusion fluid contained 3 x 10(-7) M to 10(-4) M ACh the spike frequency increased up to about 2/sec. This stimulatory effect of ACh was blocked by 10(-7) M atropine but not by 10(-3) M hexamethonium nor by 10(-5) M-d-tubocurarine. 8. The importance of Ca entry during action potentials for catecholamine secretion is discussed

Acetylcholine↗