Caffeine Contracture in Frog Cardiac Muscle after Exposure to High Concentrations of Calcium

Matsumura, Moto; Narita, Kazuhiko

doi:10.2170/jjphysiol.30.137

Cited by 4 publications

(4 citation statements)

References 9 publications

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“…However, in frog ventricle cells 'skinned' mechanically, no such cyclic contractures can be observed, perhaps because of damage to the superficial SR during the skinning process (Fabiato & Fabiato, 1978). Possibly in some way related to the present findings are those of Nayler (1973), who found that ouabain increased the amount of calcium' that could be displaced from myocardial cells by lanthanum, as well as those of Matsumura & Narita (1980), who showed that caffeine (30mM) induced contracture in frog heart muscle only when calcium was 5.4 mm, or higher; and those of Otsuka & Nonomura (1963), who found that elevated extracellular potassium induced a much larger contracture in ouabain-pretreated frog ventricular strips, although the K+-induced depolarizations were the same in control and ouabain-treated strips. These effects of K+ can also be interpreted as due to a greater calcium content of the SR induced by ouabain.…”

Section: Discussionsupporting

confidence: 40%

Differential Effects of Ouabain and 2,4‐dinitrophenol on Contractile Tension of and on Sodium and Calcium Efflux From Frog Heart Ventricular Strips

Ocampo

Orrego

1981

British J Pharmacology

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1 The efflux, from heart ventricular strips of Rana pipiens, of sodium (22Na) and calcium (45Ca) was measured simultaneously.2 22Na efflux could be resolved into two first order kinetic components: k, = 0.105 min'l, thought to represent efflux from the extracellular space, and k,l = 0.0182 min-l representing efflux from the cells.3 45Ca efflux was also resolved into an extracellular component, k, =0.1216 min'; and an intracellular one, kl, = 0.0102 min l. 45Ca k,, was greatly increased by 2,4-dinitrophenol (DNP), but unchanged by caffeine. This suggests that it represents a mitochondrial calcium compartment. 4 22Na kl, was not changed by DNP. This indicates that, at the time of DNP addition, 22Na was passively bound to undefined intracellular components. 5 Ouabain (10-6 M) decreased 45Ca efflux (k,,) initially but at later periods slightly increased it. The former effect is thought to be due to an action at the plasma membrane level, while the latter probably represents an increased exchangeability of mitochondrial calcium. The same effects were always found when ouabain was applied at different times of strip superfusion. 6 Ouabain (0.25 to 4 pM) did not decrease the k,, of 22Na efflux. Kinetic reasons are presented which indicate that, in this preparation, the activity of the sodium pump may be too fast to be measured by means of 22Na efflux, therefore these findings do not necessarily mean that ouabain does not inhibit active sodium transport. 7 The time course of the inotropic effect of ouabain was also studied in ventricular strips of Rana pipiens heart that were stimulated at 0.2 Hz with biphasic, 2 ms pulses of supramaximal intensity, and incubated in Ringer solution containing 1.1 mm calcium, or in 'calcium-free' Ringer (residual calcium: 5.2 pM), or in 'calcium-free' Ringer with 0.1 mM of the calcium chelator ethyleneglycol bis (0-aminoethylether) N,N'-tetraacetic acid (EGTA).8 In Ringer, the inotropic effect of ouabain was already observed at 5-10s after steroid addition, even with the lowest concentration tested (0.25 pM), while signs of toxicity appeared only after 15 min in 4 piM ouabain, the highest concentration used.9 When the strips were incubated in 'calcium-free' Ringer solution, force of contraction decayed to 1-2% of that in 1.1 mm calcium. Addition of 4pAM ouabain to these hypodynamic strips led to a progressive increase in contractile force of up to 300%, that started after a 50 s latency period. No signs of toxicity were observed. 10 Incubation of the strips in EGTA-Ringer also reduced contractile force to about 2% of that in Ringer, and 4 piM ouabain also increased force of contraction by approximately the same amount as seen in 'calcium-free' Ringer, but the effect began after a 10 min latency period. The concentration of calcium ion (Ca2+) in the extracellular space of strips incubated in EGTA-Ringer, was approximately 800 fold lower than in Ringer, and 60 fold lower than in 'calcium-free' Ringer solution. 11 Caffeine (20mM) induced, in strips previously incubated for 1 h in 4.4 mm cal...

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Section: Discussionsupporting

confidence: 40%

Differential Effects of Ouabain and 2,4‐dinitrophenol on Contractile Tension of and on Sodium and Calcium Efflux From Frog Heart Ventricular Strips

Ocampo

Orrego

1981

British J Pharmacology

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Section: Discussionmentioning

confidence: 98%

“…When [Na]0 is high the rate of spontaneous relaxation is fast (K2 > K1), so that the Ca released by caffeine is rapidly removed from the cell interior and the resulting contracture is weak and brief. A reduction of K2 will account for the appearance of caffeine contractures in depolarized preparations and those exposed to a very high [Ca]0 or Mn ions (Chapman & Miller, 1974;Matsumura This hypothesis shows how the contractile responses induced by caffeine in frog cardiac muscle can be very largely determined by the ionic composition of the bathing fluid even though caffeine would seem to release Ca2+ from an intracellular site. The extremely steep part of the relationship between [Na]0 and the rate of spontaneous relaxation of the caffeine contracture may be extrapolated to suggest what rate such contractures might relax in the [Na]0 of normal Ringer solution.…”

Section: Direct Comparison Of the Dependence Of The Strength Of Low-nmentioning

confidence: 96%

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The Control of the Strength of the Caffeine Contracture in Frog Atrial Trabeculae: An Activity of the Sodium‐calcium Exchange

Chapman

Tunstall

1983

Exp Physiol

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SUMMARYIn frog atrial trabeculae low-Na contractures and caffeine contractures evoked in Na-poor solutions are increased by raising the external Ca concentration ([Ca] ([Ca]i) and the fall of tension. One, also responsible for the spontaneous relaxation of the low Na contracture, is dependent on metabolic energy and may be intracellular in origin. The other depends upon the activity of the sarcolemmal Na/Ca exchange, persists in the presence of metabolic inhibitors and is also activated during a low Na contracture when [Na]0 is raised, or [Ca]o is lowered.The contractile response, of frog cardiac muscle to caffeine, would seem to be largely due to a release of Ca2+ from an intracellular store, but the strength of the resulting contracture depends upon a competition between the contractile proteins and the Na/Ca exchange for the released Ca2+.

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Aminophylline-induced contractions of rabbit ear artery in high-K+ Ca2+-free medium

Manzini

Maggi

Meli

1982

Journal of Pharmacy and Pharmacology

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Caffeine Contracture in Frog Cardiac Muscle after Exposure to High Concentrations of Calcium

Cited by 4 publications

References 9 publications

Differential Effects of Ouabain and 2,4‐dinitrophenol on Contractile Tension of and on Sodium and Calcium Efflux From Frog Heart Ventricular Strips

Differential Effects of Ouabain and 2,4‐dinitrophenol on Contractile Tension of and on Sodium and Calcium Efflux From Frog Heart Ventricular Strips

The Control of the Strength of the Caffeine Contracture in Frog Atrial Trabeculae: An Activity of the Sodium‐calcium Exchange

Aminophylline-induced contractions of rabbit ear artery in high-K+ Ca2+-free medium

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