The antagonism between Ca and Na ions on the frog's heart

Lüttgau, Hans-Christoph; Niedergerke, R.

doi:10.1113/jphysiol.1958.sp006073

Cited by 450 publications

(170 citation statements)

References 17 publications

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“…This result suggests an accumulation of Ca rather than Na as the cause of facilitation because when the external Na is decreased, the inward Na current decreases (Brady & Woodbury, 1960). When the ratio of Ca/Na2 was constant and the concentration of Ca and Na varied, the initial tension response was the same (Luttgau & Niedergerke, 1958), and consistent with Niedergerke's (1963b) finding that the influx of Ca is constant under these conditions. However, the facilitation was always less at low Ca and Na.…”

Section: Discussionsupporting

confidence: 68%

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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Section: Discussionsupporting

confidence: 68%

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

Orkand¹

1968

The Journal of Physiology

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“…Indomethacin reduced the effects of such combinations of depolarizing agents to that obtained with hydrogen peroxide in BSF. Indomethacin failed to modify the depolarizing effect of a combination of hydrogen peroxide with either cuprous or potassium ions ( (Daly & Clark, 1921;Luttgau & Niedergerke, 1958;Bohr, Seidel & Sobieski, 1969;Sitrin & Bohr, 1971). The ability of sodium ions to oppose the depolarizing effect of calcium ions on heated endothelial cells, therefore, is probably due to competition between the two cations for occupation of a cellular binding site which is important for the regulation of the membrane potential.…”

Section: Resultsmentioning

confidence: 99%

INTERACTION OF MONO‐ AND DIVALENT METALLIC CATIONS AND OF INDOMETHACIN ON THE MEMBRANE POTENTIAL OF VASCULAR ENDOTHELIAL CELLS in vitro

Northover

1975

British J Pharmacology

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Polytechnic, Leicester LE1 9BH 1 Endothelial cells depolarized progressively when heated for 5 h at 45 C in the presence of calcium (1 mM), cupric (0.08 mM) or ferrous (0.04 mM) ions. In the absence of these ions, heating caused only slight depolarization. Higher concentrations of these ions caused depolarization even at normal body temperature (37" C).2 Cuprous and potassium ions, although producing depolarization at 37 C, failed to augment the depolarization due to heating to 45 C. 3 Hydrogen peroxide caused depolarization which was potentiated by the presence of calcium, cupric or ferrous ions, but not by the presence of cuprous or potassium ions. 4 Indomethacin (0.25 mM) reduced the depolarization caused by calcium, cupric or ferrous ions at 370 C and also reduced the potentiation of heat-induced and hydrogen peroxide-induced depolarization which these divalent metallic cations produced. However, indomethacin failed to modify the depolarization caused by cuprous or potassium ions.

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“…In addition, the observation that the evoked release of noradrenaline is potentiated in a sodium-free medium (Kirpekar & Wakade, 1968a) suggests that a competition between sodium and calcium ions may exist at the sympathetic nerve endings to modulate the release of noradrenaline. Competition between these ions has been observed in the contraction of the heart (Luttgau & Niedergerke, 1958) and the release of acetylcholine at cholinergic nerve endings (Birks, Burstyn & Firth, 1968).…”

Section: Introductionmentioning

confidence: 99%