A down then up staircase in frog ventricle due to altered excitation—contraction coupling

Brown, Arthur M.; Orkand, Richard K.

doi:10.1113/jphysiol.1968.sp008560

Cited by 6 publications

(5 citation statements)

References 9 publications

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“…They found that the twitch tension staircase is negative (up to -60% in magnitude) for periods of 1 to 3 min at heart rates that do not shorten the action potential duration. We found that the rate threshold for the onset of cumulative [Ca"+o depletion is surprisingly similar to that for the negative tension staircase, i.e., 1 beat per minute (Brown and Orkand, 1968). This initial negative tension staircase may be in fact a result of the [Ca"+], depletions we have measured in this preparation.…”

Section: Discussionsupporting

confidence: 65%

“…On the other hand, frog ventricular twitch tension rapidly responds to changes in the superfusate [Ca++] (Kavaler et al, 1978). Brown and Orkand (1968) have studied the frog ventricular isometric twitch tension response to increased heart rates in the range of [Ca +]o studied here. They found that the twitch tension staircase is negative (up to -60% in magnitude) for periods of 1 to 3 min at heart rates that do not shorten the action potential duration.…”

Section: Discussionmentioning

confidence: 99%

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Extracellular calcium ion depletion in frog cardiac ventricular muscle

Dresdner¹,

Kline²

1985

Biophysical Journal

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The extracellular free [Ca++] in frog ventricular muscle strips was monitored using single-barrel calcium ion-selective microelectrodes. During trains of repetitive stimulation, a heart rate-dependent, sustained fall (depletion) of the extracellular free [Ca++] occurs, which is most likely a consequence of net Ca++ influx into ventricular cells. The magnitude of the [Ca++]0 depletion increases for higher Ringer's solution [Ca++], and is reversibly blocked by manganese ion. Prolonged repetitive field stimulation (20-30 min) activates additional cellular Ca++ efflux, which can balance the additional Ca++ influx caused by stimulation, resulting in abolition of extratrabecular [Ca++]0 depletion in 20-30 min, and hence zero net transmembrane Ca++ flux at steady state. In the poststimulation period of quiescence, cellular Ca++ efflux persists and causes an elevation (accumulation) of the extracellular free [Ca++]. From these [Ca++]0 depletions, quantitative estimates for the net transmembrane Ca++ flux were derived using an analytical solution to the diffusion equation. In the highest Ringer's solution [Ca++] used (1 mM) the calculated net increase of the total intracellular calcium per beat was 6.5 +/- 1.4 mumol/l of intracellular space. This corresponds to an average net transmembrane Ca++ influx of 0.81 +/- 0.17 pmol/cm2/s during the 800-ms action potential. In lower bath [Ca++] the net transmembrane [Ca++] flux was proportionately reduced.

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Section: Discussionsupporting

confidence: 65%

Section: Discussionmentioning

confidence: 99%

Extracellular calcium ion depletion in frog cardiac ventricular muscle

Dresdner¹,

Kline²

1985

Biophysical Journal

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“…For example, Niedergerke (1956) and Brown & Orkand (1968) attribute 'staircase' effects in the frog ventricle to changes in excitation-contraction coupling. This view is supported by the finding that no changes took place in the action potential amplitude or duration.…”

Section: Slow Inward Current Facilitation Discussionmentioning

confidence: 99%

The calcium and frequency dependence of the slow inward current ‘staircase’ in frog atrium.

Noble¹,

Shimoni²

1981

The Journal of Physiology

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SUMMARY1. Changes in the magnitude of the slow inward current in the frog atrium were monitored at different stimulation frequencies, using a double sucrose-gap technique.2. After short rest periods (1-5-3-0 min), repetitive clamp depolarizations applied at frequencies ranging from 0 33 to 1 Hz (20-60/min) resulted in a progressive increase in the slow inward current towards a new level. Action-potential amplitudes and plateau levels usually showed similar increases under these conditions. 3. Changes in the magnitude of the slow inward current were also found when the frequency was changed during constant stimulation. 4. Replacement of calcium ions by strontium or barium ions led to an augmentation or reduction, respectively, of the 'staircase' effect, relative to the effect in calcium-containing solutions. Barium ions were found to greatly increase the slow inward channel 'recovery' time.5. The results suggest that calcium influx into amphibian atrial fibres contributes to the regulation of the slow inward conductance mechanism. Progressively increasing currents may underlie positive tension staircases.

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“…6a) or included a portion of very shallow rise or even a decline of tension (cf. Brown & Orkand, 1968). These features and others, e.g.…”

mentioning

confidence: 99%

“…In these, tension changes were examined over a range of tension usually not much above the level of the line DC in Fig. 2 b so as not to exceed the region of the steepest rise in each of the 'dose-action' curves, but also not below the level BA to avoid complex effects which occur when the heart rate or calcium concentration, or both, are low, as described recently by Brown & Orkand (1968). The experiments were also limited to the period after the initial 1-2 hr of perfusion was over and heart ventricles had passed into the hypodynamic condition.…”

mentioning

confidence: 99%

Interaction between heart rate and calcium concentration in the control of contractile strength of the frog heart

Chapman¹,

Niedergerke²

1970

The Journal of Physiology

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SUMMARY1. The changes in twitch tension during the ascending and descending staircase of the frog heart have been examined under various experimental conditions including the hypodynamic and prehypodynamic state.2. The descending staircase resembles the tension change after reduction of external calcium concentration in showing two consecutive phases, an initial rapid and later slow phase of tension decline. 3. The time course of the ascending staircase depends on the condition of the heart; it is slow after, and rapid before, development of the hypodynamic state. It is also rapid when elicited after conditioning periods of increased heart rate.4. The tension transients in response to brief concentration steps of external calcium concentration were examined at various levels of heart rate. The results indicate that at high heart rates the sensitivity of heart cells to external calcium is increased.5. The results are interpreted along the lines of a previous hypothesis relating tension development to the cooperative action of two intracellular calcium compounds. The additional assumption is made that an intermediary exists which facilitates calcium movements in heart cells to an extent depending on the level of heart rate.

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A down then up staircase in frog ventricle due to altered excitation—contraction coupling

Cited by 6 publications

References 9 publications

Extracellular calcium ion depletion in frog cardiac ventricular muscle

Extracellular calcium ion depletion in frog cardiac ventricular muscle

The calcium and frequency dependence of the slow inward current ‘staircase’ in frog atrium.

Interaction between heart rate and calcium concentration in the control of contractile strength of the frog heart

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