Activity-dependent changes in the electrical behaviour of sheep cardiac Purkinje fibres

Fedida, David; Boyett, Mark R.

doi:10.1098/rspb.1985.0073

Cited by 6 publications

(2 citation statements)

References 42 publications

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“…Note that the increase in force was also accompanied, over a similar time course, by an increase in the maximum diastolic potential and a small prolongation of the action potential (Fedida & Boyett, 1985); the maximum diastolic potential increased by about 10 mV during the period of stimulation.…”

Section: Resultsmentioning

confidence: 91%

Effects of repetitive activity on developed force and intracellular sodium in isolated sheep and dog Purkinje fibres.

Boyett

Hart

Levi

et al. 1987

The Journal of Physiology

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SUMMARY1. When cardiac muscle is stimulated after a rest there is a gradual increase in force development over several minutes. The origin of this 'force staircase' was investigated in experiments on sheep and dog Purkinje fibres. Particular attention was paid to the possible role of changes in the intracellular Na+ activity (aNa).2. The first line of evidence for a role for aka came from a comparison of sheep and dog Purkinje fibres generating action potentials: after a change in the stimulus rate the slow changes of both a'a and force were monophasic in sheep but biphasic in dog preparations.3. In the remaining experiments changes in aia and force in sheep preparations were measured during 4 min trains of voltage-clamp pulses at a frequency of 2-5 Hz.4. A number of these voltage-clamp experiments also indicated that changes in aka are involved. Depending on the preparation and the duration of the pulses aka rose or fell during a train -a rise in a'a was always associated with a gradual rise in force, whereas a fall in aka was usually accompanied by a gradual fall in force.The addition of tetrodotoxin (TTX) or the use of a low holding potential reduced the progressive rises of both a'a and force, whereas the inclusion of a 10 mV hyperpolarization between pulses potentiated the progressive rises of both.5. The effect of TTX on the staircase was more marked the longer the pulses during the train; this possibly indicates that the effect of aNa on the force staircase is complex and is more marked with longer pulses. 6. A rise in aia was shown not to be the only factor underlying the progressive increase in force, because in many preparations a gradual rise in force occurred in spite of no change or even a fall of aNa.7. It is concluded that an increase in aka is involved in the slow increase in force during the staircase accompanying a train of action potentials, and that other factors are also involved; various possibilities are discussed.

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Section: Resultsmentioning

confidence: 91%

Effects of repetitive activity on developed force and intracellular sodium in isolated sheep and dog Purkinje fibres.

Boyett

Hart

Levi

et al. 1987

The Journal of Physiology

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“…The increase in m.d.p. has been attributed to activation of the electrogenic Na-K pump consequent upon a rise of intracellular Na+ activity ([Na+]i) (Vassalle, 1970;Fedida & Boyett, 1985). Fig.…”

Section: Methodsmentioning

confidence: 99%

Factors affecting intracellular sodium during repetitive activity in isolated sheep Purkinje fibres.

Boyett

Hart

Levi

1987

The Journal of Physiology

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SUMMARY1. Intracellular Na+ activity (a'a) was measured using neutral-carrier Na+-sensitive micro-electrodes in voltage-clamped sheep Purkinje fibres during and after 4 min sequences of depolarizing pulses applied to around 0 mV, at a rate of 2-5 Hz. After trains of pulse duration 50 ms the mean increase in aka was 0-65 + 0-3 mM (mean+ S.D., n = 18) whereas with longer pulse durations this rise became progressively smaller. At pulse durations of 300 ms a fall in aka was usually found.2. Recovery of aka after a pulse sequence followed a roughly exponential time course. The half-time of decline after a rise in aNa using 50 ms pulses was 111+ 52 s (n = 10), compared with a half-time of 318+ 116 s (n = 6) for recovery from a fall in aka during a sequence of 300 ms pulses.3. Application of 2 mM-Cs+ to block the pace-maker current (it) resulted in a decrease in resting aia by 0-85 + 0-45 mm (n = 6) and an outward current shift. Na+ loading during a depolarizing pulse train was greaterjn 2 mM-Cs+ than in control solution. The rise in aiNa produced by a train of 50 ms pulses in Cs+ was 1-15 + 0 4 mm (n = 10). At short pulse durations in the presence of Cs+, Na+ loading at the end of a pulse train increased as a function of pulse duration, becoming maximal at a duration of approximately 50 ms and then diminishing at longer pulse durations.4. Application of 2S5 x 10-5 M-tetrodotoxin (TTX) produced a fall in resting aNa of 0-55 + 0-2 mm (n = 6) and an outward current shift, suggesting that a TTXsensitive component of steady-state Na+ current exists at potentials in the region -65 to -80 mV.5. TTX greatly reduced the rise in a'a during a depolarizing pulse train at all pulse durations tested. A fall in aia was now found after trains of shorter pulse duration than in control solution. Similar results were obtained in the absence of TTX if the pulse train was initiated from a holding potential which was positive to the Na+ current (iNa) threshold. When iNa had been blocked, using either TTX or a low holding potential, the mean rise in aka after a train of 50 ms pulses was 0-25 + 0-2 mM (n= 8).6. The component of Na+ loading remaining at short pulse durations in the presence of TTX was abolished by 9-6 x 10-6 M-gallopamil (D600). The fall in aNa * Correspondence to Dr G. Hart, Cardiac Department, John Radcliffe Hospital, Oxford OX3 9DU.M. R. BOYETT, G. HART AND A. J. LEVI at the end of a pulse train in the presence of TTX and gallopamil increases at longer pulse durations.7. Na+ loading in TTX was unchanged or only slightly reduced by 5 mm-Mn2+. 8. The increment in aka during a pulse train was greater if the membrane was hyperpolarized during the interpulse interval.9. These results show that during repetitive activity mechanisms operate which tend to reduce aNa, namely a diminished leak current and deactivation of if, together with mechanisms which increase aka, i.e. the fast Na+ current and a second route for Na+ entry which is resistant to TTX but sensitive to gallopamil. We suggest that the TTX-insensitive component of Na+...

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Role for Sodium Channels and Intracellular Sodium in Regulation of the Cardiac Force-Frequency Relation and Contractility

January

Fozzard

1990

Developments in Cardiovascular Medicine

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Activity-dependent changes in the electrical behaviour of sheep cardiac Purkinje fibres

Cited by 6 publications

References 42 publications

Effects of repetitive activity on developed force and intracellular sodium in isolated sheep and dog Purkinje fibres.

Effects of repetitive activity on developed force and intracellular sodium in isolated sheep and dog Purkinje fibres.

Factors affecting intracellular sodium during repetitive activity in isolated sheep Purkinje fibres.

Role for Sodium Channels and Intracellular Sodium in Regulation of the Cardiac Force-Frequency Relation and Contractility

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