Effects of Barium on Mature and Embryonic Heart Cells
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Barium chloride was administered to isolated preparations of dog heart and rat atrium and to trypsinized embryonic chick heart cells cultured in vitro. Transmembrane action potentials recorded from pacemaker, specialized conductive and contractile fibers of the dog heart, and atrial fibers of rat heart showed a slowing in the rising and falling phases of the action potential and a prominent negative after-potential. The action potential of the Purkinje fiber of the dog heart showed in addition a depolarization during diastole. A decrease in resting potential was observed later. The isometric tension developed by the rat atrium showed a significant increase which was greater at the higher concentractions (greater than 3.5 x 10-4M) of barium chloride. The cultured embryonic heart cells were appreciably more sensitive to barium than the mature heart cells. An increase in rate of beat of the embryonic heart cells was observed at concentrations of 10-6M whereas a change in heart rate was first observed in the ...Keywords:
Embryonic heart
Heart cells
Diastolic depolarization
Purkinje fibers
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In the early (3-day) stage of development, long-lasting openings of the L-type Ca2+ channels (mode 2) occur in embryonic chick heart cells. Since mode-2 behavior is infrequently observed in adult heart cells of other species, in the present study, developmental change in behavior of the Ca2+ channel was examined in young (3-day) and old (17-day) embryonic chick heart cells. In the whole-cell voltage clamp, the L-type Ca2+ current carried by Ca2+ ions was smaller in amplitude and had a faster inactivation in 17-day cells than in 3-day cells. The peak current density was 8.1 +/- 0.2 microA/cm2 (mean +/- SEM, n = 5) and 5.1 +/- 0.3 microA/cm2 (n = 5) in 3-day and 17-day cells, respectively. When the charge carrier was Ba2+, the L-type Ca2+ channel current density was also smaller in 17-day cells (22.7 +/- 1.8 microA/cm2) than in 3-day cells (28.3 +/- 2.1 microA/cm2). In single-channel recordings, the mode-2 behavior was infrequent in 17-day cells compared with 3-day cells. High-open probability sweeps (with ...
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Journal Article The calcium paradox: an electrophysiological study in the isolated rabbit heart Get access A. Capucci, A. Capucci *Istituto di Cardiologia, Universitá di BolognaBologna, Italy Search for other works by this author on: Oxford Academic PubMed Google Scholar M. J. Janse, M. J. Janse †Department of Cardiology and Clinical Physiology, University of AmsterdamAmsterdam, The Netherlands Requests for reprint to M. J. Janse, M D., Department of Cardiology and Clinical Physiology, Wilhelmina Gasthuis, Eerste Helmersstraat 104, 1054 EG Amsterdam, The Netherlands Search for other works by this author on: Oxford Academic PubMed Google Scholar T. J. C. Ruigrok T. J. C. Ruigrok ‡Department of Cardiology, University HospitalUtrecht, The Netherlands Search for other works by this author on: Oxford Academic PubMed Google Scholar European Heart Journal, Volume 4, Issue suppl_H, January 1990, Pages 13–21, https://doi.org/10.1093/eurheartj/4.suppl_H.13 Published: 01 December 1983
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Transmembrane potentials were recorded in Purkinje fibers obtained from dogs aged 1 day, 1 week, 2 weeks, 4 weeks and more than 1 year. After the initial impalements there was a time-dependent increase in diastolic potential. This hyperpolarization was more pronounced in the younger Purkinje fibers. Maximum diastolic potentials from 1-day-old puppies (-78.0 ± 1.2 mV), after 10 min of continuous impalement, were significantly less negative than those for adults (-84.2 ± 1.9 mV). Fibers from neonates exposed to ouabain do not depolarize as much as fibers from adults.
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We studied the ontogenesis of the transmembrane action potential and the ultrastructure of fetal canine Purkinje fibers. Fetal hearts were obtained from fetuses just after implantation to end gestation. Using standard microelectrode recording techniques, we found that action potential characteristics varied linearly over this period of development. Maximum diastolic potential (MDP) ranged from -65 to -85 mV; action potential amplitude (AMP) varied from 100 to 120 mV; maximum upstroke velocity (Vmax) increased from 200 to 550 V/s. Action potential duration measured to 50% repolarization (APD50) increased from 15 to 156 ms while duration measured at full repolarization (APD100) similarly increased from 75 to 236 ms. The relationship between external potassium concentration and membrane potential was equivalent across all stages of fetal development. Tetrodotoxin (TTX, 7.7 X 10(-7) to 1.6 X 10(-5) M) caused concentration-dependent decreases in AMP, Vmax, and APD50. Verapamil (1 X 10(-7) to 1 X 10(-5) M) decreased Vmax and APD50 in a concentration-dependent manner. The effects of both TTX and verapamil were statistically equivalent across all stages of fetal development. Ultrastructural studies of fetal Purkinje fibers showed that myocytes at the earliest stages of development (Purkinje fibers were not visually distinct at this time) were arranged as a tightly packed mosaic with a rounded shape, with a large amount of glycogen, small sparse mitochondria, and relatively large nuclei. Mitotic cells were observed frequently. Purkinje fibers when first identified grossly had fewer myofilaments than working myocardial cells and sarcomeres without M lines. By late gestation, intercalated disks appeared with an increase in surface areas; desmosomes occurred more frequently. Myofilaments are organized around Z bands into rudimentary sarcomeres that still lack M lines. These data indicate that, although the fetal canine Purkinje fiber undergoes marked developmental changes in ultrastructure, cellular electrophysiological changes are more subtle. The action potential has a qualitative appearance similar to those of the neonatal or adult fiber. At no time during fetal development could we find slow-response action potentials.
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SummaryThe effect of acetylcholine on the beating rate of single chick embryo heart cells cultured from 8 to 10 day ventricles was determined using a new television monitor optical system. Acetylcholine had a clear negative chronotropic effect on these cells, with a threshold at 10-8-10-7 g/ml. The slowing in beating rate after the addition of acetylcholine was reversible, and was not associated with any detectable change in the inotropic state of the cells. These findings are consistent with the effect of acetylcholine on non-cultural chick embryo ventricular tissue of the same age.
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1. In chick embryo hearts, 3-day-old and not yet innervated, repetitive direct stimulation causes a transitory inhibition of the spontaneous rhythm.2. The degree of post-stimulation inhibition depends on the frequency and duration of the artificial stimulation and on the concentration of K and Ca ions in the extracellular solution.3. After treatment with atropine (10(-5) g/ml.) post-stimulation inhibition is no longer observed. The spontaneous rhythm is accelerated by atropine. The findings therefore suggest that an ACh-like substance is released from the non-innervated embryonic heart during activity.4. By use of the dorsal muscle of the leech for biological assay the liberation of an ACh-like substance from the non-innervated embryonic heart was confirmed.
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Isolated canine papillary muscles with attached false tendons were perfused with Tyrode's solution containing lidocaine. Transmembrane action potentials of ventricular muscle fibers and Purkinje fibers were recorded with glass microelectrodes. Repolarization of Purkinje fibers was accelerated by lidocaine but that of ventricular muscle fibers was unaffected. The maximum rate of rise of the action potential of Purkinje fibers decreased only at 50.0 mg/liter lidocaine; that of ventricular muscle fibers was unchanged by any concentration. The curve relating rate of rise of premature responses to level of membrane potential for Purkinje fibers was unchanged with 5.0 mg/liter but shifted down and to the right with 10.0 and 50.0 mg/liter. The effective refractory period of Purkinje fibers shortened at 5.0 and lengthened at 50.0 mg/liter. The level of membrane potential needed to elicit premature propagated responses in Purkinje fibers with a standardized test stimulus increased and the earliest responses obtained in the presence of lidocaine were relatively large. Duration of the effective refractory period of ventricular muscle fibers was unchanged with 5.0 mg/liter but lengthened progressively with 10.0 and 50.0 mg/liter. Lidocaine impaired the ability of both fibers to respond to rapid frequencies of stimulation, slowed the rate of inherent diastolic depolarization of driven Purkinje fibers, decreased the rate of discharge of spontaneously beating preparations, and minimized the increase in rate and magnitude of diastolic depolarization caused normally by epinephrine. The possible role of these effects of lidocaine in regard to its antiarrhythmic actions was discussed.
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The effects of changes in the calcium ion concentration in the medium bathin single beating cultured chick embryo ventricular cells were determined using an electro-optical monitoring technique for measuring the amplitude and velocity of cell wall motion. Although single cells showed significant decreases in the amplitude and velocity of cell wall motion during contraction when the calcium ion concentration was lowered from 1.8 mM to 0.9 mM, there were no significant changes in these parameters when the concentration was increased from 1.8 mM to 3.6 mM, and the magnitude of this response increased with increasing embryonic age. These results suggest that there is a reduced positive inotropic responsiveness in young chick embryo ventricular cells, which is particularly marked in the single cultured cell preparation because of the tendency of culturing techniques to select out immature cell populations.
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The spontaneous activity of cell clusters derived from ventricle cells of newborn rats was studied using a recording television microscope. The influence of varying concentrations of sodium, potassium, calcium, tetrodotoxin (TTX), and that of 2 mM MnCl 2 was tested. The spontaneous activity of the cell clusters persisted in TTX but it was abolished by Mn. The beating rate increased when [Ca] 0 and [Na] 0 were changed from 0.3 mM to 3.0 mM and from 30 mM to 75 mM; it decreased with a change of [Na] 0 from 75 mM to 142 mM. It is concluded that electrogenesis in these cells is determined by a slow inward current and that these cell clusters are comparable in their behavior to very young embryonic rat heart cells or cells of the rabbit sinoauricular node.
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