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Biomedical subjects

A Hirota

Publications and source records attributed to A Hirota.

At least 55 records · Page 3Linked to original sources
PubMed1993

Optical monitoring of early appearance of spontaneous membrane potential changes in the embryonic chick medulla oblongata using a voltage-sensitive dye.

Using a voltage-sensitive merocyanine-rhodamine dye (NK2761) and a 12 x 12-element photodiode matrix array, we recorded optically spontaneous membrane potential changes in a slice preparation from the embryonic chick brain stem during early development. The spontaneous optical signals, related to membrane potential changes, showed a simple monophasic shape with a relatively long duration, and they were synchronized among the different regions in the medulla oblongata. The spontaneous signals were first detected from seven-day-old embryos, and were not present in six-day-old embryos. The spontaneous signals appeared sporadically, and their frequency was very low. Three modes of optical signals termed "singlet-mode", "doublet-mode", and "triplet-mode" were observed. In the doublet- and triplet-modes, the spatial pattern of the first signal was primarily similar to that of the singlet-mode signal, whereas the signal size and spatial extent of the second and third signals appeared to decay.

Animals↗
PubMed1993

Optical assessment of spatial patterning of strength-duration relationship for vagal responses in the early embryonic chick brainstem.

The spatial patterning of strength-duration relationship for neural responses to vagus nerve stimulation in the early embryonic chick brainstem preparation was assessed by means of an optical method for monitoring neural activity using a voltage-sensitive dye. Intact brainstem, and brainstem slice preparations, together with the attached vagus nerve, were dissected from 6- to 8-day (d)-old chick embryos. They were stained with a voltage-sensitive merocyanine-rhodanine dye (NK2761). Application of depolarizing square current pulses to the vagus nerve fibers using a micro-suction electrode evoked voltage-related optical (absorption) responses in the brainstem. The optical responses were recorded simultaneously from 127 contiguous sites in both the intact and slice preparations, using a 12 x 12-element photodiode array. The amplitude of the evoked signals and the extent of the response area depended on the strength and duration of the stimulating current pulse. Thus, we determined the threshold current strength needed to evoke the fast spike-like optical signal, corresponding to the action potential, in response to vagal stimulation at a given duration, and we obtained strength-duration curves for 100-200 contiguous regions in the preparation. The strength-duration curves could be apparently fitted by the empirical formula of Weiss. From these curves we obtained the rheobasic currents as a possible indication of neural responsiveness to peripheral vagus stimulation, and we constructed the map of the spatial distribution of the rheobasic currents. The rheobasic current is smallest in the central region of the response area, and it is distributed in a layered pattern of increasing value. In accordance with such a pattern, the minimum rheobasic current decreased and the response area expanded developmentally. The results suggest that the ordered patterns of spatial distributions of the size of the axon, the specific membrane resistance, sodium channel activity, and other electrophysiological factors underlie the initial process of functional organization of the dorsal motor nucleus within the brainstem during early embryonic development.

Animals↗
PubMed1993

Optical indications of early appearance of postsynaptic potentials in the embryonic chick brain stem.

A basic problem in neurophysiology is concerned with the functional organization/architecture of the central nervous system (CNS). This problem has been studied through a variety of experiments and theoretical approaches. The ontogenetic approach is potentially a very useful strategy for analyzing the complex and subtle functional organization/architecture of the central nervous system. However, for investigations of the early embryonic CNS, conventional electrophysiological recording techniques, including microelectrodes, are extremely difficult or impossible to employ, owing to the small size, fragility and topology of the immature or newly matured neurons. For this reason, investigations of electrophysiology in the vertebrate CNS during the early phases of development have been hampered. Optical techniques using voltage-sensitive dyes have made it possible to monitor electrophysiological events in living systems that are inaccessible to microelectrodes [1, 2]. Furthermore, optical recording methods have been developed into a powerful tool for recording electrical activity simultaneously from many sites in one living preparation [3-5]. Applying these optical techniques, we have overcome traditional obstacles to functional approaches to embryonic heart and CNS during early development [6-8]. We describe here some results obtained with optical techniques in the early embryonic chick brain stem.

Animals↗
PubMed1993

Binding of antiglaucomatous drugs to synthetic melanin and their hypotensive effects on pigmented and nonpigmented rabbit eyes.

The binding of ocular hypotensive drugs to synthetic melanin was studied spectrophotometrically in vitro. The ocular hypotensive effects of the drugs, namely, timolol, befunolol, carteolol, pilocarpine, epinephrine, prostaglandin A2, F2 alpha and E2, also were compared in vivo on eyes of pigmented and albino rabbits. At an initial concentration of 10(-4) M, each of the three beta-blockers exhibited a binding rate of 80-85% as compared to only 40% for pilocarpine and 50% for epinephrine. Almost none of the prostaglandins were found to bind to synthetic melanin. Topically applied, 0.5% timolol and 3% pilocarpine significantly lowered the intraocular pressure in albino but not in pigmented rabbits. Epinephrine (1%) caused a significant reduction in the intraocular pressure both in albino and pigmented rabbits; however, the maximum reduction was greater in albino than in pigmented rabbits. Intraocular pressure was reduced to the same extent and with a similar time-course in both albino and pigmented rabbits by 0.02% prostaglandin A2, F2 alpha and E2. These findings show that several ocular hypotensive drugs bind to melanin and suggest that this process can modify the extent of their pharmacological effects when tested in a single dose, or the time-course of their effects when used to treat chronic conditions.

Adrenergic beta-Antagonists↗
PubMed1993

Measurement of calcium release from the sarcoplasmic reticulum into the myoplasm of frog cut muscle fibers.

Ca release from the sarcoplasmic reticulum of frog cut muscle fibers has been estimated with two different methods. The first method is to measure the myoplasmic free [Ca] transient under nonperturbing conditions and then estimate the amounts of Ca that are bound to the myoplasmic buffers troponin and parvalbumin. The Ca released from the sarcoplasmic reticulum is estimated from the sum of the concentrations of free Ca and of Ca bound to the indicator, to troponin, and to parvalbumin. The second method is to estimate the amount of Ca release by capturing most of the Ca with a large concentration of a high affinity Ca buffer. Both methods give similar estimates of the amount of Ca release following a single action potential and of the shape and amplitude of the release waveform.

Action Potentials↗
PubMed1992

[The effects of meaning information on heart rate, respiration, frontalis EMG, and peripheral temperature during imagery].

The present study investigated the effects of meaning information on psychophysiological responses during imagery. Eighteen undergraduates were divided into arousal and relaxation groups, which were then given arousal-meaning- and relaxation-meaning-oriented trainings, respectively. After the training, the subjects were given the imagery test, and inter-heartbeat-interval (IBI), respiration, frontalis EMG, and peripheral temperature during neutral, snake, and social imageries were analyzed. The results showed that there was a significant main effect in IBI for groups: the arousal group demonstrated greater IBI changes than the relaxation group. Regarding EMG, significant increases were present during snake and social imageries in the arousal group, whereas no significant increase was observed in the relaxation group. No significant difference between groups was found in respiration and temperature. The results suggest that there are some situations that accompany their primary meanings, and that meaning-oriented trainings can modify the structure of the response propositions.

Adolescent↗
PubMed1992

[Modulation of the adenylate cyclase-cAMP pathway by protein kinase C in chick retinal pigment epithelium].

I investigated stimulation of cyclic adenosine 3':5'-monophosphate (cAMP) production by isoproterenol and forskolin in cultured chick embryo retinal pigment epithelium. In addition, in order to study the interaction between signal transduction systems, I studied the effects of phorbol 12-myristate, 13-acetate (PMA), a protein kinase C (PKC) activator, on isoproterenol- or forskolin-stimulated cAMP production. After stimulation with 10(-9)-10(-5) M isoproterenol and forskolin, a marked and concentration-dependent increase in cAMP level was observed. However, addition of 10(-10)-10(-5) M PMA had no effect on the cAMP level. Preincubation of isoproterenol and forskolin with 100 nM PMA suppressed the increase of cAMP. The suppressive effect of PMA was stronger on isoproterenol-stimulated production than on forskolin-stimulated production. 4 alpha-phorbol 12, 13, didecanoate, a weak activator of PKC, had a weak suppressive effect on cAMP-production stimulated by isoproterenol. Both staurosporin and H-7, 1-(5-isoquinolinylsulfonyl)-methylpiperazine, inhibitors of PKC, decreased the suppression of cAMP production by PMA. It is speculated that in chick retinal pigment epithelium PKC stimulators, such as PMA, may inhibit the adenylate cyclase pathway.

Adenylyl Cyclases↗
PubMed1991

Optical detection of postsynaptic potentials evoked by vagal stimulation in the early embryonic chick brain stem slice.

1. A voltage-sensitive dye and multiple-site optical recording of changes in membrane potential were used to reveal the postsynaptic potentials in the early embryonic chick brain stem slice preparation. 2. Vagus-brain stem preparations were isolated from 8-day-old chick embryos and then transverse slice preparations were prepared with both the right and left vagus nerve fibres intact. The slice preparations were stained with a voltage-sensitive merocyanine-rhodanine dye (NK2761). 3. Voltage-related optical (absorbance) changes evoked by vagus nerve stimulation with positive square current pulses using a suction electrode were recorded simultaneously from 127 contiguous loci in the preparation, using a 12 x 12-element photodiode array. Optical responses appeared in a limited area near the dorsal surface of the stimulated side. 4. When relatively large stimulating currents were applied, optical changes having two (or sometimes three) components were recorded. One component was the fast spike-like signal and another the delayed, long-lasting slow signal. 5. The size of the slow signal was decreased by continuous stimulation, reduced by low external calcium ion concentrations and eliminated in the presence of manganese or cadmium ions. 6. The slow signals were eliminated in the presence of kynurenic acid, and they were reduced by 2-APV (DL-2-amino-5-phosphono-valeric acid) and by CNQX (6-cyano-7-nitroquinoxaline-2,3-dione). We conclude that the slow signals correspond to excitatory postsynaptic potentials which are glutamate mediated.

Action Potentials↗
PubMed1991

Optical mapping of the early development of the response pattern to vagal stimulation in embryonic chick brain stem.

1. In both intact and slice preparations of vagus-brain stem isolated from 3- to 8-day-old chick embryos, the spatial pattern of neural responses to vagal stimulation and its development were assessed by means of multiple-site optical recording of electrical activity, using a voltage-sensitive merocyanine-rhodanine dye (NK2761) and a 12 x 12-element photodiode array. 2. The first neural responses, viz. fast optical signals (related to the action potential), were recorded in the 4-day-old brain stem preparation, and slow optical signals (related to excitatory postsynaptic potentials) were detected from late 7- and 8-day-old brain stem preparations. 3. The evoked optical signals appeared to be concentrated longitudinally in the central region of the stimulated side of the intact brain stem preparation and in a limited dorsal area in the slice preparation. The signal size gradually increased and the response area expanded as development proceeded. 4. Based on the above results, we have constructed developmental maps of the spatial patterns of the fast and slow optical responses. In the maps, the positions of the peak-size regions of the fast and slow signals were assessed and we have found that there were differences in the location of these areas for the fast vs. the slow signals in the late 7- and 8-day-old embryonic brain stem preparations. 5. In the maps for the late 7- and 8-day-old embryonic brain stems, the fast signal response area seems to correspond to the dorsal motor nucleus of the vagus nerve and the slow response area to the nucleus tractus solitarii.

Action Potentials↗
PubMed1991

[Effect of topical 8-hydroxy carteolol on intraocular pressure and melanin granules].

It was reported that 8-Hydroxycarteolol (8-OH CA), the major metabolite of carteolol hydroxychloride (CA), has a slightly different pharmacological effect from CA. We studied the reduction of intraocular pressure (IOP) on a single eyedrop application of 8-OH CA in albino and pigmented rabbit eyes. To determine the characteristic of 8-OH CA and CA, we investigated the binding ability of these drugs to synthetic melanin. In the present study, topically applied 2% CA did not significantly decrease IOP in albino and pigmented rabbit eyes. Topically applied 0.01, 0.05, 0.1 and 1.0% 8-OH CA significantly decreased the IOP of albino rabbit as did 0.1 and 1.0% 8-OH to pigmented rabbit eyes. The maximum reduction of IOP was 3.5 +/- 0.33 mmHg (mean +/- SEM) in albino rabbit and 3.0 +/- 0.45 mmHg (mean +/- SEM) in pigmented rabbit. Maximum IOP reduction was obtained after 30 min. from topical application in albino rabbit, but in pigmented rabbit after 1 hour or later. Our binding studies to melanin show that the melanin binding ability is less for 8-OH CA than for CA at any concentrations. These results may indicate that lower concentrations of topically applied 8-OH CA profoundly reduce IOP compared to CA, and 8-OH CA has less effect on melanin than CA.

Administration, Topical↗
PubMed1989

Optical indications of electrical activity and excitation-contraction coupling in the early embryonic heart.

Complete understanding of the ontogenesis and early development of electrical activity and its related contraction has been hampered by our inability to apply conventional electrophysiological techniques to the early embryonic heart. Direct intracellular measurement of electrical events in the early embryonic heart is impossible because the cells are too small and frail to be impaled with microelectrodes. Optical signals from voltage-sensitive dyes have provided a new and powerful tool for monitoring changes in membrane potential in a wide variety of living preparations. With this technique it is possible to make optical recordings from cells which are inaccessible to microelectrodes. An additional advantage of the optical method for recording membrane potential activity is that electrical activity can be monitored simultaneously from many sites in a preparation. Thus, applying a multiple-site optical recording method with a 100- or 144-element photodiode array and voltage-sensitive dyes, we have been able to monitor for the first time spontaneous electrical activity in pre-fused cardiac primordia in early chick embryos at the 6- and early 7-somite stages of development; we have been able to determine that the time of initiation of the heartbeat is the middle period of the 9-somite stage. In the rat embryonic heart, the onset of spontaneous electrical activity and contraction occurs at the 3-somite stage. This article describes ionic properties of the spontaneous action potential and genesis of excitation-contraction coupling in the early embryonic chick and rat hearts. In addition, an improved view of the ontogenetic sequence of spontaneous electrical activity and its implications for excitation-contraction coupling in the early embryonic heart are proposed and discussed.

Animals↗
PubMed1989

Calcium signals recorded from two new purpurate indicators inside frog cut twitch fibers.

Two new Ca indicators, purpurate-3,3'diacetic acid (PDAA) and 1,1'-dimethylpurpurate-3,3'diacetic acid (DMPDAA), were synthesized and used to measure Ca transients in frog cut muscle fibers. These indicators are analogues of the purpurate components of murexide and tetramethylmurexide, in which two acetate groups have been incorporated into each molecule to render it membrane impermeant. The apparent dissociation constant for Ca is 0.95 mM for PDAA and 0.78 mM for DMPDAA. One of the indicators was introduced into a cut fiber, which was mounted in a double Vaseline-gap chamber, by diffusion from the end-pool solutions. The time course of indicator concentration, monitored optically in the middle of the fiber in the central-pool region, suggests that 19% of the PDAA or 27% of the DMPDAA became bound or sequestered inside the fiber. In resting fibers, the absorbance spectrum of either indicator was well fitted by the indicator's [Ca] = 0 mM cuvette absorbance spectrum, which is consistent with the idea that PDAA and DMPDAA do not enter the sarcoplasmic reticulum as tetramethylmurexide appears to be able to do (Maylie, J., M. Irving, N.L. Sizto, G. Boyarsky, and W. K. Chandler, 1987. Journal of General Physiology. 89:145-176). After an action potential, the absorbance of either indicator underwent a rapid and transient change that returned to the prestimulus baseline within 100-200 ms. The amplitude of this change had a wavelength dependence that matched the indicator's Ca-difference spectrum. The average amplitude of peak free [Ca] was 21 microM (PDAA or DMPDAA) if all the indicator inside a fiber was able to react with Ca as in cuvette calibrations, and was 26 (PDAA) or 28 microM (DMPDAA) if only freely diffusible indicator could so react. These results suggest that PDAA and DMPDAA are the first Ca indicators that provide a reliable estimate of both the amplitude and time course of (the spatial average of) free [Ca] in a twitch muscle fiber after an action potential.

Action Potentials↗
PubMed1989

Myrocin C, a new diterpene antitumor antibiotic from Myrothecium verrucaria. II. Physico-chemical properties and structure determination.

The structure of a new antitumor antibiotic, myrocin C, from a strain of Myrothecium verrucaria was characterized as a pentacyclic pimarane diterpene composed of a gamma-lactol group and a unique cyclopropane ring on the basis of its physico-chemical properties and spectroscopic data as well as a single-crystal X-ray diffraction analysis of its monoacetyl derivative.

Antibiotics, Antineoplastic↗
PubMed1989

Enhanced contractile response to noradrenaline and calcium influx in thoracic aorta isolated from dietary magnesium deficient rats.

Dependency on extracellular calcium influx in contractile response to noradrenaline has been investigated in the thoracic aorta isolated from dietary magnesium (Mg) deficient rats. Adult male Wistar rats were fed with a Mg deficient diet (0.001% Mg) for 30 days, together with control groups (0.07% Mg). The contractile response to noradrenaline in the thoracic aortas from Mg deficient rats was significantly greater than that in the controls. However, there were no significant differences between control and Mg deficient rats in the contractile response to high potassium. The rate of 45Ca uptake induced by noradrenaline was greater in Mg deficient rat aortas than in the controls, but that induced by high potassium showed no significant differences between control and Mg deficient rats. Calcium entry blockers (verapamil and nifedipine) caused a concentration-dependent depression of the noradrenaline-induced contraction. The aortas from Mg deficient rats were more sensitive to these drugs than were those from the controls. These results suggest that the noradrenaline-induced contraction depends much more on extracellular calcium influx in Mg deficient rats than in the controls.

Animals↗
PubMed1988

Functional pacemaking area in the early embryonic chick heart assessed by simultaneous multiple-site optical recording of spontaneous action potentials.

Pacemaking areas in the early embryonic chick hearts were quantitatively assessed using simultaneous multiple-site optical recordings of spontaneous action potentials. The measuring system with a 10- X 10- or a 12 X 12-element photodiode array had a spatial resolution of 15-30 microns. Spontaneous action potential-related optical signals were recorded simultaneously from multiple contiguous regions in the area in which the pacemaker site was located in seven- to nine-somite embryonic hearts stained with a voltage-sensitive merocyanine-rhodanine dye (NK 2761). In the seven- to early eight-somite embryonic hearts, the location of the pacemaking area is not uniquely determined, and as development proceeds to the nine-somite stage, the pacemaking area becomes confined to the left pre-atrial tissue. Analysis of the simultaneous multiple-site optical recordings showed that the pacemaking area was basically circular in shape in the later eight- to nine-somite embryonic hearts. An elliptical shape also was observed at the seven- to early eight-somite stages of development. The size of the pacemaking area was estimated to be approximately 1,200-3,000 micron2. We suggest that the pacemaking area is composed of approximately 60-150 cells, and that the pacemaking area remains at a relatively constant size throughout the seven- to nine-somite stages. It is thus proposed that a population of pacemaking cells, rather than a single cell, serves as a rhythm generator in the embryonic chick heart.

Action Potentials↗
PubMed1988

Methylenolactocin, a novel antitumor antibiotic from Penicillium sp.

A novel antitumor antibiotic, methylenolactocin, was isolated from the culture filtrate of a new isolate of fungus identified as Penicillium sp. The fermentation yield reached about 100 mg per liter of the broth. Methylenolactocin has the molecular formula of C11H16O4 and possess an exomethylene lactone structure. Its structure was determined to be 3-carboxy-2-methylene-4-nonanolide by spectroscopic data. It is active against some Gram-positive bacteria and it prolongs the life span of mice inoculated with Ehrlich carcinoma.

Animals↗