The effects of manganese ions on the contraction of the frog's heart

SUMMARY1. In the presence of extracellular Na ions K contractures evoked from isolated frog atria1 trabeculae show an initial phasic and a subsequent tonic contractile response.2. The phasic response shows a steep dependence on membrane potential, persists in Na-free fluid, but is blocked by Mn ions, D600 and tetracaine. It has an indirect dependence on the [Ca]0 and would seem to be associated with both the secondary inward current and the release of Ca2+ from intracellular stores.3. The tonic component of the K contracture is unaffected by D600 or tetracaine, shows a shallow dependence on membrane potential but is absent in Na-free fluid. Its tension-depolarization curve is immediately affected by alteration of either the [Ca]

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

The tension‐depolarization relationship of frog atrial trabeculae as determined by potassium contractures.

Chapman¹,

Tunstall²

1981

“…These ions presumably compete with Ca for the same binding sites on the membrane (Hagiwara & Takahashi, 1967;Langer, Serena & Nudd, 1975). They inhibit the slow inward current (Rougier, Vassort, Garnier, Gargouil & Coraboeuf, 1969;Ochi, 1970) and contractility of heart muscle (Kleinfeld & Stein, 1968;Chapman & Ellis, 1977) and the Ca uptake associated with electrical activity in squid axons (Baker, Meves & Ridgeway, 1973). Fig.…”

Section: Effect Of Mn On the Ca Induced Decrease In Internal Namentioning

confidence: 99%

Changes in the intracellular sodium activity of sheep heart Purkinje fibres produced by calcium and other divalent cations.

Deitmer¹,

Ellis²

1978

121

SUMMARY1. The intracellular Na activity of sheep heart Purkinje fibres was recorded with Na+-sensitive glass micro-electrodes. The effects of various external divalent cations on the intracellular Na activity were investigated.2. Raising the external concentration of divalent cations (Ca, Mg, Mn, Sr or Ba) from 3 to 16 mm resulted in a decrease in the intracellular Na activity of 10-50 %.3. Raising the external concentration of Ca, Sr or Ba could produce a decrease in the intracellular Na activity even when the Na-K pump was inhibited (with strophanthidin, 10-5 M); but raising the external concentration of Mg or Mn could not.4. Mn inhibited the decrease in the intracellular Na activity produced by raising external Ca while the Na-K pump was inhibited.5. Raising external Ca or adding Mn reduced the rate of rise of the intracellular Na activity on inhibition of the Na-K pump.6. The removal of external K resulted in an increase in the intracellular Na activity. This increase could be stopped and even reversed by raising external Ca.7. Removal of divalent cations from the external solution produced an increase in the intracellular Na activity. However, replacing external Ca and Mg by another divalent cation, e.g. Mn, did not result in a rise in the intracellular Na activity, except when the Na-K pump was inhibited.8. The intracellular Na activity decreased by approximately 50 % for a tenfold increase in the external Ca concentration.9. The extent of the decrease in internal Na activity produced by raising external Ca was directly proportional to the internal Na activity before external Ca was raised.10. We conclude that external Ca influences the intracellular Na activity in two ways: (a) by changing the passive Na influx: the resultant change in the intracellular Na depends on the activity of the Na-K pump; and (b) by a process where internal Na ions are exchanged for external Ca ions.

“…R. A. CHAPMAN AND C. LEOTY In mammalian cardiac muscle procaine reduces the strength of the heart beat and inhibits contractions evoked in Na-free fluid by electrical depolarization (Thorens, 1971) while tetracaine antagonizes contractures induced by the application of caffeine (Chapman & Leoty, 1976a). In amphibian heart, tetracaine and procaine inhibit the contractures initiated by caffeine, hypertonic fluids and rapid cooling in Na-free or K-rich fluids (Chapman & Miller, 1974;Chapman & Ellis, 1974;Chapman, 1978) and the phasic component ofthe K contractures (Chapman & Tunstall, 1981). Furthermore, Eisner, Lederer & Noble (1979) have noted that tetracaine also blocks the slow inward current in mammalian Purkinje fibres.…”

Section: Introductionmentioning

confidence: 99%

The effects of tetracaine on the membrane currents and contraction of frog atrial muscle.

Chapman¹,

Léoty²

1981

3. The tonic phase of contraction is little affected by tetracaine while the outward current is reduced.4. The effects of tetracaine on contraction closely resemble those obtained previously with K contractures and further emphasize that two processes, both of which depend on the membrane potential, are involved in the initiation of contraction in amphibian heart.5. The effect of tetracaine on the phasic tension would seem to be due to an inhibition of both the slow inward current and the release of Ca2+ from the sarcoplasmic reticulum.