Effects of calcium, sodium and potassium ions on contractility of isolated atria and their responses to noradrenaline

Toda, Noboru

doi:10.1111/j.1476-5381.1969.tb09510.x

Cited by 27 publications

(24 citation statements)

References 34 publications

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“…6). The contractile enhancement was dependent upon frequency of contraction, as was that observed in control preparations (9). In control and reserpine pretreated preparations the enhancement did not differ (Fig.…”

Section: Response To Noradrenalinesupporting

confidence: 74%

“…These findings suggest that endogenous noradrenaline stores are not necessary for the produc tion of changes in the contractile force. It is suggested that the values of R1 and R,j defined as the maximum driving rate which atrial contractions follow (see RESULTS), do not represent directly the refractory period but may provide parameters indicating changes in the cardiac excitability (9). Reserpine-pretreatment did not influence the values of R1 and R2.…”

Section: Discussionmentioning

confidence: 95%

“…Reserpine-pretreatment did not influence the values of R1 and R2. In contrast, noradrenaline applied to isolated atria is shown to increase the values of R1 and R, (9). Both the relative and the absolute refractory period in the dog ventricle and atrium are shortened when adrenaline or noradrenaline is infused intravenously (18,19).…”

Section: Discussionmentioning

confidence: 99%

“…The entire heart was isolated and the ventricles were dis carded. The left atrium was separated from the right along the interatrial septum (9). The left atrium preparation, from which the specialized tissues were excluded, was used for investigation of the inotropic effect of reserpine when the frequency of contraction was maintained constant by artificial electrical stimulation.…”

Section: Methodsmentioning

confidence: 99%

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Response to Sympathetic Nerve Stimulation and Noradrenaline in Atria Treated With Reserpine and in Atria From Rabbits Pretreated With Reserpine

Toda

Yamasaki

Fujiwara

1970

Japanese Journal of Pharmacology

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It is widely known that cardiac noradrenaline is markedly depleted by pretreat ment of animals with reserpine (1) but only slightly reduced by treatment of the isolated heart with reserpine (2, 3). Pretreatment of animals with reserpine depresses the reten tion of exogenous noradrenaline in the heart (4) by reducing the uptake of the amine by storage granules (5) and by increasing the destruction of the amine by monoamine oxidase in sympathetic nerve terminals (6). Reserpine when applied in vitro significantly in hibits the uptake of the amine by the isolated heart (7). Reserpine is shown to disappear almost completely from the body in a few hours when injected intravenously (8) but when applied in vitro it acts directly on the heart until the drug is washed out repeatedly. Modification by reserpine of the cardiac functions and the responsiveness of the isolated heart to endogenous and exogeneous noradrenaline would be attributed to the marked depletion of cardiac noradrenaline, the inhibition of the amine uptake by the heart and/ or the actions of reserpine per se. Although the positive chronotropic response of the heart to sympathetic nerve stimulation and to indirectly-acting sympathomimetic amines is markedly reduced and the response to noradrenaline is enhanced by pretreatment with reserpine, little is known about the effects of reserpine applied in vitro on the responses to endogenous and exogeneous noradrenaline.The present investigation was undertaken to examine (a) effects of reserpine appli ed in vitro on the chronotropic response of isolated atria to sympathetic nerve stimu lation, tyramine and exogenous noradrenaline, (b) modification of the contractile ten sion-frequency relationship and of the chronotropic and inotropic effects of noradrena line by pretreatment of animals with reserpine, and (c) effects of treatment with nor adrenaline or dopamine in the presence of monoamine oxidase inhibitor on the chrono tropic response of atria from reserpine-pretreated rabbits to tyramine and to sympathetic nerve stimulation. METHODSStudies were carried out on 43 albino rabbits of either sex, weighing 1.8 to 2.2. kg.

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Section: Response To Noradrenalinesupporting

confidence: 74%

Section: Discussionmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Response to Sympathetic Nerve Stimulation and Noradrenaline in Atria Treated With Reserpine and in Atria From Rabbits Pretreated With Reserpine

Toda

Yamasaki

Fujiwara

1970

Japanese Journal of Pharmacology

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“…The cross sectional area could not be measured because the left atrial preparations were fixed at 3 points, one hook connected to a force-displacement transducer and a pair of stimulating electrodes. Frequency-contractile force curves were obtained by raising the driving frequency stepwise from 6 to 180/min (Toda, 1969 Crosses at 'zero' min represent the atrial rate before the bathing media were replaced with Ca2+-deficient fluids.…”

Section: Methodsmentioning

confidence: 99%

Cardiotoxic and Inotropic Effects of Ouabain on Atria Isolated From Rabbits of Different Ages

Toda

1981

British J Pharmacology

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I In sino-atrial node-right atrial preparations and left atrial preparations obtained from rabbits of different ages (2 to 360 days old), cardiotoxic and inotropic effects of ouabain were compared. Tachyarrhythmias were produced in immature and mature rabbit right atria exposed for 6 to 8 min to ouabain (5 x 10-6 M). The total number of contractions before the arrhythmias developed varied inversely with age (2 to 90 days old). Percentage reductions in the resting membrane potential, overshoot and maximum rate of rise induced by ouabain were greater in mature rabbit atria than in immature rabbit atria. 2 Reduction of Ca2 + in the bathing media suppressed the development of tachyarrhythmias. 3 In electrically-driven left atria isolated from immature and mature rabbits, similar frequencycontractile force curves were obtained, maximum contractions being attained at a frequency of 120/min. Ouabain at 2 x 10-' M shifted the curve upward and at 10-6 M greatly potentiated the contractile force developed at low frequencies (6 to 30/min). Increase in contractions induced by ouabain relative to pre-drug contractions at a frequency of 60/min were greater in immature rabbit atria (15 days old) but the positive inotropic effect of 2 x 10 M ouabain relative to the effect seen at 10-6 M was appreciably less. 4 It may be concluded that atria isolated from immature rabbits tolerate higher concentrations of ouabain than those isolated from mature rabbits.

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Cardiac

Gallacher¹,

Gintant²,

Abi‐Gerges³

et al. 2016

Drug Discovery Toxicology

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Effects of calcium, sodium and potassium ions on contractility of isolated atria and their responses to noradrenaline

Cited by 27 publications

References 34 publications

Response to Sympathetic Nerve Stimulation and Noradrenaline in Atria Treated With Reserpine and in Atria From Rabbits Pretreated With Reserpine

Response to Sympathetic Nerve Stimulation and Noradrenaline in Atria Treated With Reserpine and in Atria From Rabbits Pretreated With Reserpine

Cardiotoxic and Inotropic Effects of Ouabain on Atria Isolated From Rabbits of Different Ages

Cardiac

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