Sodium-calcium exchange in Purkinje fibers: Electrical and mechanical effects

Li, Tung; Vassalle, Mario

doi:10.1007/bf02070164

Cited by 16 publications

(5 citation statements)

References 22 publications

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“…2). In view of the well-accepted relationship between inotropy, the ratio of extracellular calcium-to-sodium, and calcium loading of the SR (14,22), we interpreted these results as evidence for age-related differences in calcium loading and/or of the SR. In support of this interpretation, the inotropic effects of increasing extracellular calcium-to-sodium ratio on postrest contraction of immature atrial strips was use dependent (Fig.…”

Section: Discussionmentioning

confidence: 77%

Effects of Postnatal Maturation on Postrest Potentiation in Isolated Rabbit Atria

et al. 1987

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ABSTRACT. Ultrastructural changes in cardiac sarcoplasmic reticulum (SR) have been reported during postnatal development of the mammalian heart, but the functional significance of these observations has not been well characterized. Calcium release from SR in intact myocardial preparations was determined by the contractile characteristics of postrest contractions. Isometric tension and the maximum rate of tension development of the first contraction following intervals of electromechanical quiescence (rest) were related to steady-state tension and maximum rate of tension development during contraction at constant frequency (1.0 Hz) in isolated left atrial strips from newborn (1-7 days), immature (14-21 days), and adult (more than 6 months) rabbits. The first postrest contraction was increased as a function of the rest interval rate of tension development, defined as postrest potentiation, in all three age groups and reached a maximum value at rest intervals of more than 20 s. Tension developed by the first contraction following a 60-s rest interval was potentiated less in newborn and immature atria than in adult atria at an extracellular calcium concentration ([Ca],) of 2.5 mM, an age-related difference most marked in the immature. Ryanodine (5.0 x M), a putative blocker of calcium release from cardiac SR, abolished postrest potentiation providing evidence that calcium release from SR is the predominant determinant of the postrest contraction. Postrest tension in atria from the immature rabbit heart was significantly increased both in absolute terms and relative to steady-state tension following stabilization under conditions which increase intracellular [Ca] ([Cali), i.e. increasing [Ca],, increasing tonicity, or decreasing extracellular sodium concentration ([Na],). In contrast, postrest tension in atria from the adult rabbit heart decreased relative to steady-state tension under conditions that increase [Cali. Rest potentiated contraction to a similar extent in both age groups (approximately 300% of steady-state) but this maximum was obtained under markedly different ionic conditions. Maximum postrest potentiation occurred at 2.5 mM [Ca], and 153.0 mM [Na], in the adult atria whereas maximum potentiation occurred at 5.0 mM [Ca], and 87.0 mM [Na], in immature atria. Results from experiments in which [Ca], was increased during a 60-s rest interval suggest that the predominant effects of [Ca], on postrest potentiation are attributable to [Ca],-dependent changes in [Cali as opposed to rest-dependent changes in

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Section: Discussionmentioning

confidence: 77%

Effects of Postnatal Maturation on Postrest Potentiation in Isolated Rabbit Atria

et al. 1987

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“…Lee & Dagostino (1982), Im & Lee (1984) and Vassalle & Lee (1984) have investigated the effect of strophanthidin in dog Purkinje fibres and did not find any hysteresis between force and aNa. This may reflect a genuine difference between sheep and dog Purkinje fibres, and it can be added to a number of other differences recently noted between these two species: strophanthidin causes a reproducible elevation of the action potential plateau in sheep Purkinje fibres but causes little effect on action potential shape in dog fibres (Lee & Dagostino, 1982;Wier & Hess, 1984); the responses ofthe two species to a change ofstimulation rate are different (Boyett, Hart, Levi & Roberts, 1985); the two species also respond differently to a change of the bathing Ca concentration (Li & Vassalle, 1983;Weir & Hess, 1984). Thus, it is possible that there may be differences in the way strophanthidin causes increased force in the two species; the relation between force and aka may be simpler in dog than in sheep Purkinje fibres.…”

Section: Discussionmentioning

confidence: 99%

Dissociation between force and intracellular sodium activity with strophanthidin in isolated sheep Purkinje fibres.

Boyett¹,

Hart²,

Levi³

1986

The Journal of Physiology

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SUMMARY1. We have recorded membrane potential, intracellular Na activity (aika) and force of contraction in sheep Purkinje fibres. Force and aia were recorded continuously and simultaneously during exposure to strophanthidin and its subsequent washing off.2. Exposure to strophanthidin in concentrations of 1-5 x 10-7, 5 x 10-7 and 10-5 M caused an increase in force of contraction which was temporally dissociated from the increase of aba.3. There was hysteresis in the relationship between force and aia when the period of increasing force was compared to the period of decreasing force. When force increased on exposure to strophanthidin, the same aka was always associated with a higher force than when force was decreasing while washing off the drug.4. For the same rise of aa higher doses of strophanthidin produced larger rises of force than lower doses.5. When diphenylhydantoin was present in the bathing solution at concentrations of 10-5 and 10-4 M, the relation between force and aia with 10-5 M-strophanthidin had a less steep slope, but still displayed hysteresis.6. The relationship between force and aka during changes of the bathing K concentration also displayed a hysteresis, which was in the same direction as that found with strophanthidin.7. These results are discussed in relation to proposed mechanisms of action of strophanthidin and more generally in relation to the factors linking force of contraction and aNa. We conclude that in sheep Purkinje fibres the increase of force caused by strophanthidin is not solely due to an increase of a, and that other interventions can also result in hysteresis between force and aNa.

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“…The shortening was also significant, as tested in 4 preparations (Table 2-IV). It is expected that perfusion with low [Na+]o leads to an increase in [Ca2+]; (Li and VASSALLE, 1983), as is the case with the application of ouabain (LANCER, 1981;Li and VASSALLE, 1983). In Table 2 (III and IV), it is evident that both procedures shortened the CL significantly and the resultant CLs (0.8 + 0.2 and 0.8 + 0.1 s) were much the same as the CL of intact preparations from the group 2 patients (1.1 +0.3 s).…”

Section: Resultsmentioning

confidence: 99%

“…This increase in [Na+J; results in an increase in [Ca2 +]; via an Na-Ca exchange mechanism (LI and VASSALLE, 1983). If the ouabain-induced shortening of the CL is due to an increase in [Ca2 +];, the CL should be shortened during perfusion with Tyrode solution containing low [Na+]o because a reduction in [Na +] o depresses the out-going transport of Ca2 + from the cell through suppression of Na-Ca exchange and increases [Ca2 +]; (LI and VASSALLE, 1983). Since we obtained evidence for this effect (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…In guinea-pig ventricular muscles, a limited range of mechanical stretch presumably release Cat + from the sarcoplasmic reticulum (NAKAGAWA et al, 1987). In the enlarged human atria there is an inhibition of the sarcolemmal Na-K ATPase activity and a derangement of anionic binding site of glycocalyx on the sarcolemmal surface (LEE, 1986), both of which also result in an increase in [Ca2+]; (LANCER, 1978(LANCER, ,1981LI and VASSALLE, 1983). Therefore proportional shortening of the CL of automaticity encountered on the progressive dilatation of right atrium may be, at least in part, a reflection of the gradual increase in the intracellular Cat + concentration.…”

Section: Discussionmentioning

confidence: 99%

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Two differential mechanisms of automaticity in diseased human atrial fibers.

et al. 1988

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The ionic mechanisms of automaticity in spontaneously active preparations (n = 38) from "diseased" human atria were investigated. The cycle length (CL) of the automatic action potential (AAP) ranged from 0.6 to 4.5 s (mean + S.D.: 2.0 + 1.0 s). The AAP from preparations obtained from non-digitalized patients (group 1, n = 29) showed various CLs, in that 16 patients had a CL longer than 2.0 s (slow-type AAP) while in tissues from the other 13 patients, the CL was 2.0 s or less (fast-type AAP). On the other hand, all preparations obtained from the digitalized patients prior to cardiac surgery (group 2, n = 9) had the fast-type AAP (CL <_ 2.0 s). The slow-type AAP was accelerated and changed to the fast one after application of ouabain (1 µM) or by perfusing with 50% [Na + ]o Tyrode solution. Ryanodine (1 tiM), a specific inhibitor of calcium release from the sarcoplasmic reticulum (SR), markedly lengthened the CL of fast-type AAP, without affecting the slow-type AAP. In contrast, caffeine (15 mM) shortened the CL of the slow-type AAP and remarkably lengthened the CL of the fast-type AAP, as is the case in ryanodine. The rate of slow-type AAP was enhanced with an increase in [Ca2+]o and depressed with a decrease in [Ca2 +]o or with application of diltiazem, a Ca2 + channel blocker. The slow-type AAP was changed to the fast-type AAP by stretching the preparation by about 20%. In vitro preparations excised from patients with dilated atria revealed a shorter CL of AAPs. We conclude that in "diseased" human atrial preparations, the ionic mechanism responsible for generation of slow-and fast-type automaticity differs. Slow automaticity (CL >2.0 s) perhaps relates to activation of the slow inward Ca2 + current, while the fast-type automaticity (CL <2.0 s) is linked to cyclic increases in [Ca2 +]~.

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Sodium-calcium exchange in Purkinje fibers: Electrical and mechanical effects

Cited by 16 publications

References 22 publications

Effects of Postnatal Maturation on Postrest Potentiation in Isolated Rabbit Atria

Effects of Postnatal Maturation on Postrest Potentiation in Isolated Rabbit Atria

Dissociation between force and intracellular sodium activity with strophanthidin in isolated sheep Purkinje fibres.

Two differential mechanisms of automaticity in diseased human atrial fibers.

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