Mechanische Reaktionen des Frosch- und S�ugetiermyokards bei Ver�nderung der Aktionspotential-Dauer durch konstante Gleichstromimpulse

286

105

4. The ability of a fibre bundle to contract again after a preceding twitch is greatly dependent on the membrane potential between two equal depolarizations. In Tyrode solutions with 1*8 and 7-2 mM-CaCl2 half restoration of this ability occurred at -45 + 3 mV ( + s.E. of mean) and -23 + 4 mV, respectively. 5. In sodium-free bathing solutions, steady-state tension was attained upon the first depolarization provided ICa was activated.

Section: Introductionmentioning

confidence: 68%

The relation between membrane potential, membrane currents and activation of contraction in ventricular myocardial fibres

Beeler¹,

Réuter²

1970

286

105

“…We therefore sought a possible delayed effect via the internal store of activator (Morad & Goldman, 1973) and subsequent release after completion of a time-dependent process. Evidence for this in the isolated preparation (Antoni et al 1969) required confirmation in the intact animal, because the properties ofthe isolated myocardium are altered (Reichel, 1976). …”

Section: Discussionmentioning

confidence: 99%

“…Allen (1977) in a study of isolated cat papillary muscle concluded that 'changes in action potential durations do not necessarily make an important contribution to the changes in tension of papillary muscles'. However, Antoni, Jacob & Kaufmann (1969) had previously shown that an increase in duration of the action potential caused a much larger effect on the contractility of the subsequent beat than of the concomitant beat. Contractility is thought to reflect the amount of calcium released to react with the contractile system, provided that the sensitivity of the contractile proteins to calcium is constant (for references see Chapman, Coray & McGuigan, 1983).…”

Section: Introductionmentioning

confidence: 98%

“…Contractility is thought to reflect the amount of calcium released to react with the contractile system, provided that the sensitivity of the contractile proteins to calcium is constant (for references see Chapman, Coray & McGuigan, 1983). The experiment of Antoni et al (1969) can therefore be interpreted as implying that extra calcium enters the cell during a prolonged action potential and is stored intracellularly until the following contraction. In the time between contractions the calcium can be postulated to be sited in the internal calcium store (Morad & Goldman, 1973).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Cardiac action potential duration and contractility in the intact dog heart.

Drake-Holland¹,

Noble²,

Pieterse³

et al. 1983

SUMMARY1. The maximum rate of rise of left ventricular pressure (DP) and action potential duration (a.p.d.) were measured in closed-chest anaesthetized dogs with atrioventricular dissociation and fl-adrenergic blockade. Right ventricular stimulation was carried out with protocols consisting of a conditioning 'priming' period and a test period.2. When a single test stimulus was introduced at varying intervals after the priming period, DP was found to be maximal at 800-1000 ms. With this single test stimulus fixed at the optimum, DP was found to be a variable inverse function of the a.p.d. of the same beat; no positive correlation could be found between DP and a.p.d.3. When a second test stimulus at the optimum interval was introduced after the first, the DP (DP2) was found to be strongly dependent on that elicited by the first test stimulus (DP1); the relationship was positive, linear, independent of the method used to vary DP, and independent of whether DP1 was depressed or potentiated. The slope of the relationship was less than 1I0 and the line passed through the point where DP2 = DP1; this is the point of continuous stimulation at the optimum interval in a steady state. 4. This result is consistent with the hypothesis that the coefficient relating DP1 to DP2, at constant a.p.d. of the first test pulse (AP1), is an index of the proportion of the activator of contraction stored during relaxation of test beat 1 which is released again on beat 2.5. In order to test the hypothesis that the remaining contractility depended on the action potential of test beat 1, AP1 was varied by changing the intervals between the priming stimuli.

“…This behaviour is similar to that described by Edman & Johannsson (1976) for isolated rabbit papillary muscle, and is considered to be due to the fact that contractility depends on the amount of calcium ion in a labile store which takes time to 'fill'. Many studies in isolated heart muscle have demonstrated the second factor, namely that prolongation of the action potential causes a longer tension development (longer time to peak tension) which contributes to a higher tension (Wood et al 1969;Antoni, Jacob & Kaufmann, 1969;Blinks, Olson, Jewell & Braveny, 1972;Allen et al 1976;Wohlfart, 1979). The rate of rise of tension and therefore the related index we use, the rate of rise of pressure (dPiv/dtmax) (Van den Bos et al 1973) is independent of the duration of contractile activity, i.e.…”

Section: Determinants Of Contractilitymentioning

confidence: 99%

The action‐potential duration and contractile response of the intact heart related to the preceding interval and the preceding beat in the dog and cat

Elzinga

Lab

Noble

et al. 1981

SUMMARY1. Simultaneous measurements were made in anaesthetized dogs of monophasic action potentials from the right ventricle and of the maximum rate of rise of left ventricular pressure (dPiv/dtmax). Atrio-ventricular dissociation was induced and the heart paced via right ventricular electrodes.2. A control period of steady pacing was followed by a test stimulus after a variable interval called the 'test-pulse interval'. The duration of the action potential of the test beat (measured at 70 % repolarization) increased with test-pulse interval and reached an approximately steady value at intervals of 10-1-5 sec. This constitutes the electrical restitution curve'.3. An increase in the frequency of stimulation prior to the introduction of the test pulses caused a downward displacement of the electrical restitution curve.4. Stimulation at 2 Hz and paired pulse stimulation at 1 Hz (same number of stimuli per min) were introduced prior to the test pulses and produced very similar electrical restitution curves.5. For a constant frequency of stimulation in the control period, adrenaline produced downward displacement of the restitution curve.6. It is concluded that there is no obvious relationship between the restitution of the action potential duration and of the contractile response. We suggest therefore that electrical and mechanical restitution occur through separate processes, the former through time-dependent recovery in membrane conductances and the latter through time-dependent increase in availability of intracellular calcium for release.7. Contractions were introduced with a test-pulse interval shorter than the optimum, and were followed by a second test pulse fixed at the optimum interval of 0-8-1 0 sec. The second test beats were potentiated (post-extrasystolic potentiation). In isolated ejecting cat hearts, there was an optimum interval for the first test pulse * Address for correspondence. G. ELZINGA AND OTHERS to produce the greatest potentiation of the second test beat. This interval was 0-2-0{3 sec, and was shortened by an increase in frequency of stimulation prior to the first test beat.8. The interval preceding the first test pulse was then varied within a range (0-8-2-0 sec) which did not produce potentiation. These first test pulses were sometimes preceded by one extrasystole. The timing of this extrasystole was altered to vary the post-extrastolic potentiation of the first test pulse.9. Multiple regression analysis, carried out between dPiv/dtmax of the second test pulse (DP2, the dependent variable) and the action potential duration (AP1) and dPiv/dtmax (DP1) of the first test pulse (independent variables) yielded correlation coefficients between 0x88 and 0 99. Each determination of the coefficient included data from beats with and without post-extrasystolic potentiation.10. It is postulated that the coefficient relating DP2 to DP1 in the multiple regression analysis (mean value 0 75) is an index of the proportion of calcium stored during relaxation which is released again on the next beat.11. When...