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T Yada

Publications and source records attributed to T Yada.

At least 163 records · Page 9Linked to original sources
PubMed1986

Downregulation of cell-to-cell communication by the viral src gene is blocked by TMB-8 and recovery of communication is blocked by vanadate.

The viral src gene downregulates junctional communication, closing cell-to-cell membrane channels presumably by way of the phosphoinositide signal route. We show that TMB-8 [8-N, N-(diethylamino) octyl-3,4,5-trimethoxybenzoate] counteracts this downregulation in cells transformed by temperature-sensitive mutant Rous sarcoma virus: TMB-8 (36-72 microM) raises junctional permeability when applied during activity of src protein kinase, i.e., at steady permissive temperature; and TMB-8 inhibits the fall of junctional permeability, when the activity of src protein kinase gets turned on. TMB-8 also (reversibly) inhibits the growth of the cells at permissive temperature and reverses the morphological changes associated with transformation. The morphological reversal lags several hours behind the junctional-permeability reversal. Communication recovers within a few minutes when the activity of the src protein kinase is turned off (in absence of TMB-8). Sodium orthovanadate (20 microM) prevents this recovery, but it has no major effect on junctional permeability on its own. We discuss possible modes of action of these agents on critical stages of the signal route, related to intracellular Ca2+ and protein kinase C.

Animals↗
PubMed1986

[Right ventricular ischemia evaluated by radionuclide ventriculography].

The clinical usefulness of radionuclide ventriculography (RNV) was evaluated in patients with right ventricular ischemia. The subjects consisted of 25 patients with acute inferior myocardial infarction, 19 patients with old myocardial infarction and six patients with angina pectoris who had severe stenosis of the right coronary artery. In patients with acute inferior myocardial infarction, follow-up radionuclide studies were performed during the recovery periods on the first, 7th-14th, and 30th hospital day. Fifteen of the 25 patients initially had decreased right ventricular ejection fractions (evidence of right ventricular infarction). The mean value was 28 +/- 8% on the initial day, but 7-14 days and 30 days after the acute attack, it improved markedly to 36 +/- 9% and 39 +/- 9%, respectively. Regional wall motion abnormality resolved in 10 of the 15 patients on the 30th hospital day. In 25 patients with old myocardial infarction or with angina pectoris, RNV was performed at rest and during supine exercise to determine the influence or right coronary artery disease. Right ventricular ejection fraction was changed by exercise from 42 +/- 7% to 44 +/- 10% in patients with proximal artery lesions, and from 45 +/- 7% to 50 +/- 10% in patients with distal artery lesions. Right ventricular ejection fraction increased in patients with isolated right coronary artery disease (rest: 44 +/- 8%, exercise: 49 +/- 9%), decreased in patients with combined left anterior descending artery disease (rest: 40 +/- 6%, exercise: 38 +/- 11%) and increased in patients with combined circumflex artery disease (rest: 43 +/- 5%, exercise: 47 +/- 6%). We concluded that right ventricular infarction is a frequent complication in patients with inferior myocardial infarction. However, right ventricular ejection fraction and right ventricular regional wall motion abnormality improve dramatically within one month. Stress-induced ischemia would be rare in patients with isolated right coronary artery disease. The above findings support the notion that the right ventricular myocardium has peculiar coronary perfusions.

Angina Pectoris↗
PubMed1985

HeLa cells have histamine H1-receptors which mediate activation of the K+ conductance.

HeLa cells responded to exogenous histamine with a transient hyperpolarization due to increased membrane conductance to K+. After successive applications of histamine, the cell membrane became virtually unresponsive (desensitized). The responses were blocked by pyrilamine but not by cimetidine. Thus, it appears that HeLa cells have H1-receptors which mediate an increase in the K+ conductance.

Cell Membrane↗
PubMed1985

Diacylglycerol downregulates junctional membrane permeability. TMB-8 blocks this effect.

We tested the question whether junctional cell-to-cell communication is regulated by the diacylglycerol branch of the phosphoinositide transmembrane signal pathway. Cultured epithelial rat liver cells were treated with the synthetic diacylglycerol 1-oleoyl-2-acetyl glycerol, while their junctional permeability was probed with the microinjected 443-dalton fluorescent tracer Lucifer Yellow. The treatment reduced junctional permeability (without affecting Lucifer permeability of nonjunctional cell membrane). The effect was dose dependent, with a threshold of about 25 micrograms diacylglycerol/ml in sparse cultures and about 50 micrograms/ml in confluent cultures. The reduction of junctional permeability began within 3 min of diacylglycerol application, peaked within 20 min, and reversed spontaneously within 90 min. The phorbol ester TPA mimicked the diacylglycerol effect, but the (spontaneous) reversal was slower. We propose that cell-to-cell communication is under dual physiological control: an up-regulatory one, as exerted by the cyclic AMP signal route (Loewenstein, W.R., 1985, Biochem. Soc. Symp. London, 50: 43-58), and a downregulatory one, by the diacylglycerol signal route. TMB-8 (54-70 microM)--a blocker of intracellular Ca2+ mobilization--impeded the diacylglycerol action on junctional permeability. It prevented the effect of low diacylglycerol doses completely and it markedly reduced the effect of high doses. (It also counteracted the effect of TPA.) Ca2+ thus emerges as a possible candidate for a role in the junctional downregulation by the diacylglycerol signal route. We tentatively advance two models. In one, leaning closely on the Calcium Hypothesis of cell-to-cell channel regulation (Loewenstein, W.R., 1966, Ann. N.Y. Acad. Sci. 137:441-472), Ca2+ mediates the action of the route on the channel. In the other, Ca2+ acts farther removed from the channel, on protein kinase C. Calmidazolium (5-10 microM)--an inhibitor of calmodulinactivated proteins--did not prevent the diacylglycerol-induced reduction of junctional permeability. Nor did sodium orthovanadate (25 or 50 microM)--an inhibitor of tyrosyl phosphatase--prevent the reversal of diacylglycerol-induced (or TPA-induced) reduction of junctional permeability.

Animals↗
PubMed1985

Development of electrical rhythmic activity in early embryonic cultured chick double-heart monitored optically with a voltage-sensitive dye.

Double-hearted embryos were produced by whole-embryo culture of chick embryos which were microsurgically cut through the tissue of the anterior intestinal portal at the 1- to 6-somite developmental stage, at the time when the cardiac primordia have not yet fused in the bulboventricular region. The cultured embryos were removed from an incubator usually at the 7- to 10-somite stages of development, and then spontaneous electrical action potentials and/or contractions were optically recorded simultaneously from both the right and left half-hearts, using a 10 X 10- element photodiode matrix array together with a voltage-sensitive merocyanine-rhodanine dye (NK 2761). At the 7- to 8-somite stages, spontaneous action potentials were detected from bilateral prebeating half-hearts or sometimes from one half-heart. In each half-heart, the first spontaneous beating was often observed in the half-heart of the 9 somite embryos. In the beating half-hearts regular activity was always observed, while in the prebeating half-hearts at the 7- to 8-somite stages, both the regular and irregular rhythms of action potentials were detected, and the incidence of occurrence of regular activity significantly outnumbered that of the irregular rhythm. The heart rate in the left half-heart was faster than that in the right half-heart in the great majority of the prebeating and beating double-hearted embryos.

Action Potentials↗
PubMed1985

Effects of calcium on electrical propagation in early embryonic precontractile heart as revealed by multiple-site optical recording of action potentials.

The effects of Ca2+ on electrical propagation in early embryonic precontractile chick hearts were studied optically using a voltage-sensitive merocyanine-rhodanine dye. Spontaneous optical signals, corresponding to action potentials, were recorded simultaneously from 25 separate regions of the eight-to-nine-somite embryonic primitive heart, using a square photodiode array. Electrical propagation was assessed by analyzing the timing of the signals obtained from different regions. Electrical propagation in the heart was suppressed by either lowering or raising extracellular Ca2+. Similar effects were produced by a Ca2+ ionophore (A23187). We have also found that electrical propagation across the primordial fusion line at the midline of the heart was enhanced by increasing, and depressed by lowering, external Ca2+. One possible interpretation is that intercellular communication in the embryonic precontractile heart is regulated by the level of the intracellular Ca2+ concentration, and it is suggested that intercellular communication across the primordial fusion line strongly depends on external Ca2+.

Action Potentials↗
PubMed1985

Optical studies of excitation-contraction coupling in the early embryonic chick heart.

Excitation-contraction coupling at the onset of beating in the 9-10-somite embryonic chick heart was studied by means of an optical method together with a voltage-sensitive merocyanine-rhodanine dye. Spontaneous optical signals were recorded simultaneously from many areas of the embryonic heart, using a square photodiode matrix array. At time of initiation of the heartbeat, spontaneous optical signals consisting of two components were often detected. The first component (1st signal) is a dye-related absorption change due to the action potential, and the second component (2nd signal) is a light scattering change due to contraction. When Ca2+ in the bathing solution was partly replaced by Mg2+, the peak size of both signals was reduced. The correlation between the 1st and 2nd signals corresponded to the relationship between excitation and contraction. The formation of excitation-contraction coupling exhibited a regional non-uniformity in the developing 9-10-somite embryonic hearts: contraction was first generated in the right ventricular region, and then the contractile area spread widely over the whole of the heart. The curves of the excitation-related 1st signal vs. the contraction-related 2nd signal obtained from different areas were not superimposable. Decoupling of excitation from contraction was produced by raising the Ca2+ concentration in the bathing solution, by lowering the Na2+ concentration or by inclusion of a Ca2+ ionophore (A23187). Replacement of the bathing solution with D2O or hypertonic solution also suppressed excitation-contraction coupling. The results suggest that in the early embryonic initial beating chick heart, the contractile system is activated by Ca2+ influx across the sarcolemma accompanying the action potential, and that a Na+-Ca2+ exchange mechanism participates in the relaxation phase of the heartbeat.

Action Potentials↗
PubMed1985

Early events in development of electrical activity and contraction in embryonic rat heart assessed by optical recording.

Spontaneous action potential and contraction in the early embryonic heart of the rat have been monitored optically using a voltage-sensitive merocyanine-rhodanine dye together with a multiple-element photodiode matrix array, and the onset of rhythmical action-potential activity in the early phases of rat cardiogenesis was conclusively determined for the first time. Spontaneous rhythmical action potentials were first generated in the central part of the embryonic heart at the middle period of the 3-somite stage of development, at 91/2 days after copulation. Subsequently, contractions coupled with the action potential also appeared at the end of the 3-somite stage. Usually, at the 3-somite stage, spontaneous action signals were synchronized among the different areas in the heart. From this result, it is evident that the paired right and left cardiac primordia are fused completely at the time of initiation of spontaneous electrical activity. In the 3-somite embryonic heart, excitatory waves were conducted radially over the heart, at a uniform rate (0.4-0.8 mm/s), from the pace-making area. However, the regional priority of pace-making activity is not rigid but is flexible.

Action Potentials↗
PubMed1984

Electrical activity of an intestinal epithelial cell line: hyperpolarizing responses to intestinal secretagogues.

Cultured epithelial cells (Intestine 407) derived from fetal human small intestine exhibited spontaneous oscillations of membrane potential between the resting level of about -20 mV and the activated level of about -75 mV. The cells were hyperpolarized to the latter level in response to mechanical or electrical stimuli. The hyperpolarizing responses were also elicited by the application of intestinal secretagogues: acetylcholine, histamine, serotonin and vasoactive intestinal polypeptide (VIP). The spontaneous oscillation of membrane potential became prominent and long-lasting in the presence of acetylcholine, histamine, serotonin or VIP. These secretagogue-induced responses were mediated by individual independent receptors on the cell membrane. Muscarinic receptors were responsible for the acetylcholine response, and H1-receptors for the histamine response. The cells also responded with a slow hyperpolarization to calcium ionophore A23187, which is known to induce intestinal secretion. The spontaneously occurring hyperpolarizing responses and those induced by stimuli were both due to an increase in the K+ conductance of the cell membrane. Since acetylcholine, histamine, serotonin and A23187 are known to promote mobilization of cellular Ca2+ ions in intestinal secretory cells, it is hypothesized that these electrical activities of the cell are closely related to the receptor stimulation which leads to the Ca2+-mediated intestinal secretion.

Acetylcholine↗
PubMed1984

Exogenous ATP induces electrical membrane responses in fibroblasts.

Mouse fibroblastic L cells responded to exogenous ATP (greater than or equal to 0.2 mM) with a transient hyperpolarization due to increased membrane permeability to K+. By contrast, intracellular injection of ATP (up to about 3 mM) produced no noticeable effects on the membrane potential. The effects of a non-hydrolysable analogue of ATP (AMP-PNP) were similar to those of ATP. After successive applications of ATP, the cell membrane became virtually unresponsive (desensitized). Extracellular ADP was also effective, but AMP or adenosine was not. Antazoline suppressed the ATP response. Thus, exogenous ATP and ADP appear to stimulate P2- purinoceptors . Similar responses to ATP (or ADP) were also observed in human normal diploid fibroblasts (Flow 1000 line).

Adenosine Diphosphate↗
PubMed1982

Calcium channel and calcium pump involved in oscillatory hyperpolarizing responses of L-strain mouse fibroblasts.

1. In fibroblastic L cells, spontaneously repeated hyperpolarizing responses (oscillation of membrane potential) and hyperpolarizing responses evoked by electrical stimuli were suppressed by the external application of a K(+) channel blocker, nonyltriethylammonium (C(9)). This hydrophobic TEA-analogue also inhibited the hyperpolarization induced by intracellular Ca(2+) injection.2. Quinine or quinidine, known inhibitors of the Ca(2+)-activated K(+) channel of red cells, instantaneously inhibited these hyperpolarizations. Thus, these hyperpolarizations are likely to be caused by the operation of Ca(2+)-sensitive K(+) channels.3. Azide, which is known to inhibit the mitochondrial Ca(2+) uptake in fibroblasts, and caffeine, dantrolene Na and oxalate, which affect the microsomal Ca(2+) transport, did not exert any effects upon the electrical potential profiles.4. On the other hand, Ca(2+) channel blockers (nifedipine, D 600 and Co(2+)) suppressed the hyperpolarizing responses, but not the hyperpolarizations produced by intracellular Ca(2+) injection, suggesting that the calcium ions responsible for the hyperpolarizing responses are mainly derived from outside the cell through Ca(2+) channels.5. Flavones of plant origin, which are known to inhibit Ca(2+)-ATPase, prolonged the duration of the hyperpolarizing phase of the oscillation or produced a sustained hyperpolarization.6. It is concluded that the Ca(2+) channel and the Ca(2+) pump play essential roles in the generation of the hyperpolarizing response and of the membrane potential oscillation in L cells, and that these hyperpolarizations are brought about by a transient elevation of cytosolic Ca(2+) level which, in turn, activates Ca(2+)-dependent K(+) channels.

Animals↗
PubMed1981

Phagocytic activity and hyperpolarizing responses in L-strain mouse fibroblasts.

1. Fibroblastic L cells not only respond with a slow hyperpolarizing potential change to a mechanical or electrical stimulus but also show spontaneous, repetitive hyperpolarizations (i.e. membrane potential oscillation). 2. Almost all the cells can actively take up latex beads whose surfaces were treated by U.V. irradiation. 3. Non-phagocytic L cells hardly showed hyperpolarizing responses, while hyperpolarizing responses were obtained in all the phagocytic L cells. The exposure of the cell surface to beads, however, did not trigger the generation of hyperpolarizing responses. 4. Metabolic inhibitors, low temperature and cytochalasin B inhibited both the uptake of beads and the hyperpolarizing responses. 5. Increasing the external concentration of Ca2+ induced a remarkable stimulation of the phagocytosis of beads. Mg2+ and Ba2+, which inhibited hyperpolarizing responses due to competition for Ca2+ sites on the outer surface of the membrane, significantly suppressed the uptake of beads. 6. Verapamil, a Ca2+ channel blocker, inhibited not only hyperpolarizing membrane responses but also ingestion of beads. 7. It is concluded that the Ca2+ inflow on the hyperpolarizing membrane responses is closely associated with the phagocytic activity in L cells, probably through activation of the microfilament assembly.

Animals↗
PubMed1981

Oscillation of intracellular Cl- activity and membrane potential in cultured fibroblasts (L cells).

The intracellular Cl-activity (aCli) and the membrane potential (Vm) were simultaneously measured in cultured L-strain fibroblasts, using a Cl- selective liquid ion-exchanger microelectrode and a standard microelectrode. The oscillations of aCli and Vm were found to occur concomitantly. A decrease in the aCli value was associated with the spontaneous hyperpolarization. The depolarization produced by current injection resulted in an increase in aCli. These data suggest that the membrane permeability to Cl- is significantly high during the Vm oscillation in the L cell.

Animals↗
PubMed1979

Induction and repair of DNA strand breaks in cultured mammalian cells following fast neutron irradiation.

Induction and repair of DNA breaks following irradiation with NIRS cyclotron neutrons were studied in cultured mammalian cells (L5178Y) in comparison to those following gamma-rays. The yield of the total single-strand breaks, 3'OH terminals and sites susceptible to S1 endonuclease following fast neutrons was found to be approximately 50 per cent of that following gamma-irradiation. On the other hand, the yield of double-strand breaks was slightly higher after fast neutrons than after gamma-rays. The percentage of the total single-strand breaks remaining unrejoined at 3 hours after post-irradiation incubation was found to be distinctly higher after the fast neutrons than after gamma-rays. The neutron-induced damage appears to carry a higher proportion of alkali-labile lesions compared to gamma-rays. It was concluded that the increase in the yield of double-strand breaks and of unrejoinable breaks is responsible for a high r.b.e. of the cyclotron neutrons.

Animals↗
PubMed1978

Induction and repair of strand breaks and 3'-hydroxy terminals in the DNA of mouse brain following gamma irradiation.

DNA was isolated from mouse brain after in vivo gamma-ray irradiation, treated with endonuclease S1 from Aspergillus oryzae if necessary, and analysed further by alkaline and neutral sucrose gradient centrifugation. In parallel, its template activity was determined by DNA polymerase (EC 2.7.7.7, enzyme A of Klenow from Escherichia coli) assay as described previously. Similar experiments were performed with cultured mouse leukaemia cells (L5178Y) irradiated in vitro at 0 degrees C. Irradiation induced single- and double-strand breaks in the DNA of the brain with a yield of 1.0 and 0.1 break per 10(12) dalton per rad (100 eV/break and 770 eV/break), respectively. The yield of single-strand breaks in the brain was lower than that found in the cultured cells, whereas the yield of double-strand breaks was found to be almost the same in both cases. Treatment of irradiated DNA with single-strand-specific S1 endonuclease gave rise to further breaks detected on neutral sucrose gradient analysis. The yield of these breaks was also higher in the brain compared to the cultured cells. The increase per unit dose in the template activity of the DNA from the brain was found to be five times as much as that found in the cultured cells. Then, the average number of deoxyribonucleotides incorporated per break was determined on DNA which had experienced different treatments. The value for the brain DNA irradiated in vivo was found to be five times as much as that found for DNA treated with pancreatic deoxyribonuclease and 10 times as much as those found for DNA from the cultured cells and isolated brain nuclei irradiated in vitro at 0 degrees C. Thus, in vivo irradiation seemed to induce gaps with 3'-OH terminals in addition to simple breaks with or without 3'-OH terminals found in the cultured cells. Radiation-induced single-strand breaks and 3'-OH terminals in the DNA of the brain were repaired following irradiation. Approx. 20--40% of the terminals or breaks induced were, however, remaining at 3 h or more after irradiation, depending on the dose administered.

Animals↗
PubMedDate not supplied

Pituitary adenylate cyclase activating polypeptide (PACAP) increases cytosolic-free calcium concentration in folliculo-stellate cells and somatotropes of rat pituitary.

Pituitary adenylate cyclase activating polypeptide (PACAP) is a new member of the secretin/VIP peptide family. In order to identify pituitary target cells for PACAP, we examined the effect of PACAP on the cytosolic-free Ca2+ concentrations, [Ca2+]i, in cells using Fura-2 and a digital imaging system. In a concentration-dependent manner, PACAP increased [Ca2+]i in pituitary cells, from 10(-11) to 10(-8) M. Some cells responded to PACAP at 10(-11) M, while others only at 10(-8) M, showing a diversity among cells in the sensitivity to PACAP. Both PACAP and growth hormone-releasing factor (GRF) at 10(-8) M increased [Ca2+]i in 25% and 33% of the total pituitary cells, respectively. About 38% of the GRF-responsive cells also responded to PACAP. Some of the cells that responded to PACAP were immunocytochemically identified as growth hormone (GH) cells or folliculo-stellate (FS) cells using antisera against GH or S-100 protein, respectively. The results indicate that both the folliculo-stellate cells and GH cells of the pituitary are the direct targets for PACAP, but the possibility that other cell types also respond to PACAP cannot be excluded.

Animals↗