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Biomedical subjects

A Hirota

Publications and source records attributed to A Hirota.

At least 91 records · Page 5Linked to original sources
PubMed1983

Initial development of conduction pattern of spontaneous action potential in early embryonic precontractile chick heart.

The conduction of spontaneous action potentials in the 7-10 somite embryonic developing chick hearts was monitored optically using a potential-sensitive merocyanine-rhodanine dye. Spontaneous optical action signals from 5 to 12 different regions of the primitive heart were recorded simultaneously. Short delays were observed among firing times of the absorption signals which were nearly synchronized among the different regions. From these delays, we estimated the conduction velocity of the spontaneous excitatory waves. Usually, in the 7-somite to the beginning of the 9-somite stage, (i) excitatory waves conducted radially over one side of the prebeating heart, at a uniform rate; (ii) the "radially" spreading electrical wave slowed considerably within the primordial fusion line at the midline of the heart; and (iii) this delay disappeared in the later period of the 9-somite stage to the 10-somite stage. These observations suggest that electrical coupling among the cells within the primordial fusion line is poor during the 7 to 9-somite stage, and that the coupling is strengthened by the late 9th or 10th somite stage.

Action Potentials↗
PubMed1983

Flexibility of regional pacemaking priority in early embryonic heart monitored by simultaneous optical recording of action potentials from multiple sites.

The propagation of spontaneous action potentials in 7-9 somite embryonic pre-contractile chick hearts was measured optically using a potential-sensitive merocyanine-rhodanine dye. Spontaneous optical signals, corresponding to action potentials, were recorded simultaneously from 8-16 different sites of the primitive embryonic heart. Short delays were observed in the time of occurrence of optical signals obtained from the different regions. We have found (i) switching phenomena: the site exhibiting pacemaking priority was first situated in the right pre-atrium, double pacemakers: two different pacemaking areas were situated independently in the right and left pre-atrial portions of the heart. On the basis of analysis of such behavior, it was concluded that the regional priority of the pacemaking activity is not rigid but is flexible, that and the direction of the spread of excitation is adaptable to the circumstances in the early embryonic heart.

Action Potentials↗
PubMed1983

Temperature dependence of spontaneous electrical activity in early embryonic heart monitored optically with a potential-sensitive dye.

The effects of temperature on spontaneous action potential activity in the 7-9 somite embryonic precontractile chick hearts were investigated using an optical method for monitoring membrane potential. A potential-sensitive merocyanine-rhodanine dye was used as an optical probe. Cooling caused a marked decrease in the frequency of occurrence of the spontaneous action potential. This slowing was associated with a decreased rate of diastolic depolarization of the pacemaker action potential. When the temperature was lowered, a decrease in the rate of rise and a prolongation of duration of the optical action signal also occurred. In addition, cooling resulted in a disordering of the rhythmicity of the action potential, and a decrease in the conduction velocity of excitation. Q10 values for such parameters were calculated: there were slight decreases in the Q10 values for the frequency and conduction velocity for 7-9 somite embryonic hearts.

Action Potentials↗
PubMed1981

Localization of pacemaking activity in early embryonic heart monitored using voltage-sensitive dye.

Early in cardiogenesis, heart primordia are brought together at the midline and fuse with each other progressively caudally-- this results in the formation of the primitive tubular heart which begins beating spontaneously at the middle period of the 9-somite developmental stage in the chick embryo. However, in these very early stages of development, the myocardial cells are small and technically difficult to impale with microelectrodes; thus electrophysiological studies on the very early embryonic heart are rare. Recently, potential sensitive dye-related absorption signals have provided a new method for monitoring spontaneous action potential activity in the early embryonic heart. This technique is based on the observation that changes in potential across membrane(s) stained with certain voltage-sensitive dyes are accompanied by changes in their optical properties (absorption, fluorescence, and/or birefringence). Using absorption signals, we have already demonstrated in embryonic pre-beating chick heart in the 7-8-somite stages, the occurrence of action potential activity, development of pacemaker potential and cardiac rhythm generation. With this method, originally introduced to record neuronal activity in invertebrate ganglia, many cells or portions of the preparation can be monitored simultaneously. Accordingly we have expanded the optical recording apparatus to monitor simultaneously spontaneous action potentials from five portions of an early embryonic heart, and report here experiments carried out on the embryonic hearts of chicks (white Leghorn) at the 7-11-somite developmental stages, corresponding to 25-35 h of incubation. The hearts attached to the embryo were stained with a merocyanine-rhodamine dye (NK2761) as a potentiometric probe. This dye is analogue of Dye XVII or Dye XXIII.

Action Potentials↗
PubMed1981

Optical recording of development of electrical activity in embryonic chick heart during early phases of cardiogenesis.

1. Developmental changes in the spontaneous action potential were measured using optical signals from early embryonic chick heart stained with a potential sensitive merocyanine-rhodanine dye. 2. The wave-length dependence of the dye signal is triphasic in early embryonic chick heart with a decrease in absorption from 525 to 600 nm, an increase from 625 to 720 nm, and a decrease at 750 nm. The signal was largest at 700 nm. 3. The magnitude of the spontaneous absorption signal increased as the development of the embryonic heart proceeded. In addition, the magnitude of the absorption signal differed among the various regions of an early embryonic chick heart and the number of electrically active cells increased dramatically throughout the 7-9 somite developmental stages. 4. The number of the electrically active cells was largest in the right portion of the ventricle at the 7-9 somite developmental stages. 5. The shape of spontaneous absorption signals could be classified into four types in the developmental stages between 7 and 9 somites: Signals resembling the cardiac action potential and the pace-maker potential were not recorded until the 8-9 somite developmental stage.

Absorption↗
PubMed1981

Optical indications of pace-maker potential and rhythm generation in early embryonic chick heart.

1. Pace-maker type action potentials and rhythm generation in very early embryonic chick hearts have been monitored using a voltage-sensitive merocyanine-rhodanine dye. 2. Rhythmicity in recurrence of the spontaneous action potentials was evident at the 7 somite developmental stage, and the rhythm was completely organized by the early period of the 9 somite stage; just before the first contraction. The rhythmic recurrence of action potentials was increased in frequency as development proceeded from the 7 to the 9 somite stage, and presumably gives rise to the rhythm of the initial contractions. 3. Optical signals resembling the pace-maker type action potential with a diastolic depolarization phase were first detected in embryonic hearts at the 8 somite stage. At this stage, pace-maker type action potentials were detected from various regions, such as the ventricle and the unfused primordia at the atrium level. 4. Regionalization of pace-maker type action signals was exhibited at the early period of the 9 somite stage. At this stage, the pace-maker type signals were often evident at the atrium level, while the cardiac type signals were detected in the ventricular region. 5. Hence it is concluded (i) that the rhythmicity has already been generated at the 7 somite developmental stage, (ii) that the pace-making cells are widely distributed in the embryonic hearts at the 7-8 somite stages and (iii) that the appearance of the pace-maker potential is initially localized to the atrium level at about the 9-10 somite stages.

Action Potentials↗
PubMed1981

Action potential synchrony in embryonic precontractile chick heart: optical monitoring with potentiometric dyes.

1. Using an optical method for monitoring membrane potential, we recorded spontaneous action potentials simultaneously in several different areas of the 7-9 somite embryonic chick hearts. 2. Absorption signals resembling spontaneous action potentials were well synchronized among the different areas in the prebeating embryonic heart during the 7-9 somite stages of development, and the synchronization spread over the entire area of the heart. From these experimental results, it is evident that there is electrical coupling among embryonic chick heart cells even in the early stages of cardiogenesis. 3. When an embryonic heart was separated into right and left or anterior and posterior parts, the action potential synchrony between the two halves was completely blocked; however, the synchrony and the intrinsic rhythmicity in action potential recurrence remained in each part.

Action Potentials↗
PubMed1981

Optical recording of conducted action potential in heart muscle using a voltage-sensitive dye.

The absorption signals of a merocyanine-rhodanine dye in response to action potential were measured on the bullfrog atrium. Simultaneous recording of optical signals and membrane potential showed the same time course within 15 to 30 min after exposure to Ca2+- free solution. The action spectrum of the dye exhibited a triphasic pattern with a decrease in absorption between 530 and 600 nm, an increase between 640 and 720 nm and a decrease at 750 nm. Using five photodetectors we have able to simultaneously monitor the action potential from five different regions of the preparation. The conduction velocity could be measured even in Ca2+- free solution; the velocity measured optically by the simultaneous multi-recording method was equal to that obtained with a microelectrode measurement. Thus, the optical method can validly be used to solve some problems on arrhythmia-related mechanism.

Action Potentials↗
PubMed1980

Optical signals from early embryonic chick heart stained with potential sensitive dyes: evidence for electrical activity.

1. Using an optical method for monitoring membrane potential, spontaneous electrical activity in the very early embryonic chick heart at the 7-9 somite stages was measured. 2. Spontaneous absorption signals from the 7-8 somite embryonic chick hearts stained with a potential sensitive merocyanine-oxazolone dye were demonstrated. The signals were observed also when a merocyanine-rhodanine dye was used. These signals were identified as spontaneous electrical activity in the embryonic heart cells. 3. The action spectrum in absorption of the merocyanine-oxazolone dye was triphasic in early embryonic chick heart with an increase in transmittance from 750 to 700, a decrease from 700 to 600, and an increase from 600 to 525 nm. 4. The magnitude of the signal was about 10(-3) of the resting intensity at 675 nm, with the merocyanine-oxazolone dye. The spontaneous absorption signals had a signal-to-noise ratio of about 10, respectively. 5. The absorption signals were markedly depressed by a higher external K+-concentration, however, were not affected by tetrodotoxin (TTX). 6. The results indicate that spontaneous electrical activity is generated at the 7-9 somite developmental stage before the initiation of heartbeat.

Absorption↗