ACTION OF CALCIUM ON ELECTRICAL AND MECHANICAL ACTIVITIES OF THE CULTURED CHICK EMBRYONIC HEART
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Abstract:
By the methods of intracellular microelectrode technique and the bridge circuit for recording the mechanical activity, the effect of external calcium concentration of the cultured chick embryonic heart has been investigated. Trypsin-dispersed cells from the ventricle of 5 days old chick embryos were cultured. The cell clusters became attached to the bottom of cultured-dish. Then, results from trypsin-dispersed cells were compared with those of noncultured intact embryonic hearts. Spontaneous cells were compared with those of non-cultured intact embryonic hearts. Spontaneous cells were discarded and only quiescent cells were driven by electrical field stimulation.1. The reduction of calcium in the external medium strikingly prolonged the duration of action potential in cultured cells, while the amplitude of mechanical activity was prominently decreased.2. In the intact embryonic hearts, the configuration of action potential is not significantly affected by the calcium deficient solution. On the other hand, the effect of calcium deficiency on mechanical activity is more dramatic than that in cultured cells. These results suggest that the inward movement of calcium ion through the membrane plays a significant role in the initiation of contraction.3. The reduced mechanical activity of cultured and intact cells due to calci um deficiency returns to its normal level by the application of g-strophanthin, but the recovery rate was larger in cultured cells.Keywords:
Embryonic heart
Heart cells
Calcium in biology
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 ...
Heart cells
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Calcium in biology
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Heart cells
Embryonic heart
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Embryonic heart
Heart cells
Primary culture
Heart development
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The isolated cardiac myocytes of rats were immediately infected by cosackievirus B3(CVB3) to investigate the effects of such procedure on the cell cycle, apoptosis and intracellular ionized calcium (Ca2+ i) of cardiac myocytes. Newborn Balb/c murine cardiac myocytes were cultivated,then infected by CVB3. Intracellular Ca2+ i was measured by flow cytometer. The calcium in the medium for culturing cardiac myocytes was detected by using atom absorb spectrum test. It was found that CVB3 could markedly inhibit the differentiation and proliferation of the infected cardiac myocytes and induce the apoptosis. The intracellular Ca2+ i level in the infected group was significantly higher than in the control group (P＜0. 01). The calcium concentration in the medium for culturing cardiac myocytes in the infected group was significantly lower than in the control group (P＜0.05). It was suggested that the apoptosis and intracellular calcium overload of the CVB3-affected cardiac myocytes are likely to play an important role in the pathogenesis of viral myocarditis.
Calcium in biology
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Beat (acoustics)
Embryonic heart
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Heart beat
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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 -4 M) 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 -6 M whereas a change in heart rate was first observed in the adult heart at concentrations above 10 -4 M. The induction of beating in cell communities previously quiescent is due to a local automatic activity rather than to a propagated activity from an adjacent cell community. The slowing in rise time of the action potential can be attributed to a depression of the sodium-carrying system. The slowing of repolarization can be ascribed to a decrease in potassium conductance. The pronounced negative after-potential can be explained on the basis of sustained impermeability of the membrane to potassium. The mechanism by which barium produces a positive inotropic effect in the rat atrium is open to conjecture. It cannot be attributed solely to a prolongation of the duration of the action potential nor can a direct effect on the contractile proteins be excluded. The presence of extracellular calcium is essential in order to obtain a positive inotropic effect in the rat atrium when barium is added.
Embryonic heart
Heart cells
Purkinje fibers
Atrial action potential
Diastolic depolarization
Barium chloride
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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 ...
Embryonic heart
Heart cells
Diastolic depolarization
Purkinje fibers
Barium chloride
Heart beat
Atrium (architecture)
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The rates of uptake and oxidation of glucose, lactate, pyruvate, and palmitate were measured for "mixed" cultures of rat heart cells that exhibit a myocyte-to-fibroblast ratio similar to that observed in vivo. Glucose uptake and conversion to lactate were also measured using enriched cultures of myocytes and fibroblasts. The metabolism of mixed cultures, which contain 70-80% myocytes, closely resembles that of enriched myocyte cultures. The energy production and substrate oxidation rates of cultured neonatal heart cells, adult myocytes, and perfused hearts are compared. It appears that the energy requirements of cultured heart cells are much lower than that of whole tissue. The results suggest that the metabolism of cultured heart cells may be basically the same as those in vivo but appears to be different because of reduced energy requirements in culture.
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Primary culture
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