Movements of Ca in beating ventricles of the frog heart

Niedergerke, R.

doi:10.1113/jphysiol.1963.sp007167

Cited by 196 publications

(107 citation statements)

References 18 publications

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“…The values obtained for/3 in each of the two preparations were 8.92 X 103 cm -1 and 8.60 X 103 cm -1 (mean value of ~ = 8.76 X 108 cm -1) (see Table II). These values are comparable to those obtained for the area per volume ratio of frog ventricle (35,36) and agree very closely with those area per volume values obtained for mass cultures of embryonic chick heart cells (37) as well as embryonic chick right ventricle (34).…”

Section: Morphometrysupporting

confidence: 78%

A synthetic strand of cardiac muscle: its passive electrical properties.

Lieberman¹,

Sawanobori²,

Kootsey³

et al. 1975

The Journal of General Physiology

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A B S T R n O T The passive electrical properties of synthetic strands of cardiac muscle, grown in tissue culture, were studied using two intraeeUular microelectrodes: one to inject a rectangular pulse of current and the other to record the resultant displacement of membrane potential at various distances from the current source. In all preparations, the potential displacement, instead of approaching a steady value as would be expected for a cell with constant electrical properties, increased slowly with time throughout the current step. In such circumstances, the specific electrical constants for the membrane and cytoplasm must not be obtained by applying the usual methods, which are based on the analytical solution of the partial differential equation describing a one-dimensional cell with constant electrical properties. A satisfactory fit of the potential waveforms was, however, obtained with numerical solutions of a modified form of this equation in which the membrane resistance increased linearly with time. Best fits of the waveforms from 12 preparations gave the foUowing values for the membrane resistance times unit length, membrane capacitance per unit length, and for the myoplasmic resistance: 1.22 4-0.13 X 10 ~ f~cm, 0.224 4-0.023 # F . c m -x, and 1.37 -4-0.13 X 107 ~crn -t, respectively. The value of membrane capacitance per unit length was close to that obtained from the time constant of the foot of the action potential and was in keeping with the generally satisfactory fit of the recorded waveforms with solutions of the cable equation in which the membrane impedance is that of a single capacitor and resistor in parallel. The area of membrane per unit length and the cross-sectional area of myoplasm at any given length of the preparation were determined from light and composite electron micrographs, and these were used to calculate the foUowing values for the specific electrical membrane resistance, membrane capacitance, and the resistivity of the cytoplasm: 20.5 + 3.0 )< 103 ftcm z, 1.54 4-0.24 #F.cm-", and 180 -4-34 ~cm, respectively. I N T R O D U C T I O NIn cardiac muscle, as in other excitable cells, the passive electrical properties of the cell m e m b r a n e a n d cytoplasm must be d e t e r m i n e d from observations of

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Section: Morphometrysupporting

confidence: 78%

A synthetic strand of cardiac muscle: its passive electrical properties.

Lieberman¹,

Sawanobori²,

Kootsey³

et al. 1975

The Journal of General Physiology

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“…Ca influx is also increased at constant external Ca when the Na concentration is reduced (Niedergerke, 1963b). Under these conditions in the present experiments, the facilitation also increased.…”

Section: Discussionsupporting

confidence: 66%

Facilitation of heart muscle contraction and its dependence on external calcium and sodium

Orkand¹

1968

The Journal of Physiology

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SUMMARY1. The magnitude and time course of the facilitation of contraction following previous stimulation have been studied in strips of frog ventricle when the external concentrations of Na and Ca were varied. The maximum tension and the maximum rate of rise of tension have been used as indices of activation of the contractile element. Under the experimental conditions these two parameters changed similarly.2. At low stimulus frequencies (3-12 beats/min), and moderate concentrations of external Ca (2-5 mM), the facilitation of contraction with repetitive stimulation can be predicted by assuming each contraction to produce an amount of facilitation which sums linearly with that remaining from previous responses. Thus, the staircase can be constructed from the decay of facilitation following a single contraction.3. The decay of facilitation appears to consist of two components. The first has a half-time of about 3 sec; the second about 50 sec. The decay of the second component of facilitation is slowed and its magnitude increased by raising the external Ca from 2 to 5 mm.4. Reducing the external Na concentration increases both the initial strength of contraction and the amount of facilitation.5. When the ratio Ca/Na2 is kept constant while changing the Ca and Na concentrations, the first contraction in a series remains constant, but facilitation is less at low concentrations of Ca and Na. Facilitation, therefore, does not depend solely on the amount of initial activation of the contractile system. 6. The results are consistent with the hypothesis that facilitation depends on the amount of calcium retained in some cellular store.

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“…The inotropic effect of ketamine was significantly reduced when the atria were incubated in low Na or in high Ca solutions, i.e. when the Ca influx was already largely increased (Niedergerke, 1963). (4) Ketamine, at concentrations below 5 x 10-4 M, increased significantly the 45Ca uptake in electrically driven atria, which seems to confirm that the increase in Ca influx is involved in the positive inotropic effect of the drug.…”

Section: Ketamine Interaction With Reserpine Practolol and Isoprenalinesupporting

confidence: 63%

“…is increased or the Na is reduced (Wildbrandt & Koller, 1948). In both situations Ca influx into atrial cells is increased (Niedergerke, 1963 Figure 5, the effect of ketamine was dependent upon …”

Section: Dose-responses To Ketamine In Right and Left Atrial Preparatmentioning

confidence: 99%

The Mechanism of the Positive Inotropic Action of Ketamine on Isolated Atria of the Rat

Barrigón

Miguel

Tamargo

et al. 1982

British J Pharmacology

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1 The effect of ketamine (10-7 M-5 x 10-4 M) on electrical and mechanical properties of isolated atria of the rat was investigated. 2 On spontaneously beating right atria, ketamine produced a dose-dependent positive inotropic effect which was accompanied by a progressive reduction in atrial rate. 3 In electrically driven left atria, ketamine produced a dose-dependent positive inotropic effect which was accompanied by a parallel increase in df/dtm,, and by a prolongation in the time to peak tension and in the time for total contraction. The positive inotropic effect occurred concomitantly with an increase in the height and duration of the plateau phase of the action potential of atrial fibres. 4 The positive inotropic effect of ketamine varied with the concentration of Ca and Na in the bathing media and the rate of stimulation. 5 Ketamine decreased post-extrasystolic potentiation and the amplitude-interval relationship. 6 The positive inotropic effect of ketamine was inhibited by verapamil (10-6 M) and by caffeine (4x 103 M).7 Ketamine, 5 x 10-5 M and 10-4 M, increased 45Ca uptake in electrically driven left atria. At 10-4 M and 5 x 10-4 M, ketamine also increased 45Ca efflux. 8 These results suggest that ketamine produces its positive inotropic effect by two possible mechanisms. One of these is presumed to be an effect on the cell membrane which leads to an increased Ca influx into atrial fibres; the other is probably related to the inhibition of Ca sequestration by the sarcoplasmic reticulum.

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Movements of Ca in beating ventricles of the frog heart

Cited by 196 publications

References 18 publications

A synthetic strand of cardiac muscle: its passive electrical properties.

A synthetic strand of cardiac muscle: its passive electrical properties.

Facilitation of heart muscle contraction and its dependence on external calcium and sodium

The Mechanism of the Positive Inotropic Action of Ketamine on Isolated Atria of the Rat

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