Summary
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1.
In frog atria, time and voltage dependence of inactivation and reactivation of fast transient Na current were studied using the sucrose-gap voltage clamp technique. Experiments were done at 4–7° C.
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2.
Fast inward current inactivated by conditioning depolarizing clamps. The relation between steady-state inactivation and membrane potential is represented by an S-shaped curve similar to that observed in squid axon. At the resting level the availability of the Na-carrying system is about 60–70%.
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During depolarizing clamps inactivation of Na current follows an approximately exponential time course with time constants between 1.5 and 8 msec.
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Recovery from inactivation (reactivation) is much slower than development of inactivation. Time constants between 100 and 600 msec were observed during the recovery process following a repolarization or a hyperpolarization.
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A ratio between the time constants of inactivation and reactivation in the order of 1∶50 was found when the two processes were studied at the same potential level.
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6.
In the frog atrial action potential the slow reactivation of the Na system is reflected by a relative refractory period reaching far beyond full repolarization.
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7.
Assuming that the slow course of Na reactivation is an inherent feature of Na kinetics, the inactivation variable (h) of the Hodgkin-Huxley theory (1952d) seems inadequate to describe the inactivation-reactivation process in frog atria. Formally fast inactivation and slow reactivation could be accounted for by replacing the variableh with two variables which both decrease on depolarization but largely differ in the rate constants.
Zusammenfassung
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1.
In “voltage-clamp”-Messungen mittels der Saccharose-Trennwandmethode wurde die Inaktivierung des raschen Na-Einstroms am Froschvorhof bei Temperaturen zwischen 4 und 7° C untersucht.
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2.
Die Größe des Na-Stromes, der auf einem gegebenen Potentialniveau ausgelöst werden kann, ist eine S-Funktion des Vorpotentials (stationäre Inaktivierung). Bei Potentialen unterhalb −100 mV ist der Na-Strom maximal, bei Potentialen oberhalb −30 mV ist er praktisch Null.
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3.
In depolarisierenden Klemmen verläuft die Inaktivierung des Na-Stroms angenähert exponentiell mit Zeitkonstanten zwischen 1,5 und 8 msec.
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4.
Die Rückbildung der Inaktivierung (Reaktivierung des Na-Systems) nach einer Repolarisation oder Hyperpolarisation verläuft mit Zeitkonstanten zwischen 100 und 600 msec.
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5.
Bei kombinierter Messung der Inaktivierung und Reaktivierung auf gegebenem Potentialniveau (nach Potentialsprüngen von einem niedrigeren bzw. höheren Niveau aus) verhalten sich die Zeitkonstanten der beiden Vorgänge etwa wie 1∶50.
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6.
Im Aktionspotential des Froschvorhofs ist die langsame Reaktivierung des Na-Systems daran zu erkennen, daß die relative Refraktärzeit weit über die volle Repolarisation hinausreicht.
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7.
Der langsame Ablauf der Na-Reaktivierung ist wahrscheinlich nicht durch sekundäre Faktoren bedingt, sondern auf die molekulare Kinetik des Prozesses zu beziehen. Formal kann man die unterschiedliche Geschwindigkeit der Inaktivierung und Reaktivierung dadurch beschreiben, daß man die Variableh der Hodgkin-Huxley-Theorie durch zwei Variablen ersetzt, die in ihrer Zeitabhängigkeit stark differieren.
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References
Adelman, W. J., Jr., Palti, Y.: The influence of external potassium on the inactivation of sodium currents in the giant axon of the squid, Loligo pealei. J. gen. Physiol.53, 685–703 (1969).
Antoni, H., Delius, W.: Nachweis von zwei Komponenten in der Anstiegsphase des Aktionspotentials von Froschmyokardfasern. Pflügers Arch. ges. Physiol.283, 187–202 (1965).
Beeler, G. W., Jr., Reuter, H.: Voltage clamp experiments on ventricular myocardial fibres. J. Physiol. (Lond.)207, 165–190 (1970a).
——: Membrane calcium current in ventricular myocardial fibres. J. Physiol. (Lond.)207, 191–209 (1970b).
——: The relation between membrane potential, membrane currents and activation of contraction in ventricular myocardial fibres. J. Physiol. (Lond.)207, 211–229 (1970c).
Chandler, W. K., Hodgkin, A. L., Meves, H.: The effect of changing the internal solution on sodium inactivation and related phenomena in giant axons. J. Physiol. (Lond.)180, 821–836 (1965).
Dudel, J., Peper, K., Rüdel, R., Trautwein, W.: Excitatory membrane current in heart muscle (Purkinje fibers). Pflügers Arch. ges. Physiol.292, 255–273 (1966).
Dudel, J., Rüdel, R.: Voltage and time dependence of excitatory sodium current in cooled sheep Purkinje fibres. Pflügers Arch.315, 136–158 (1970).
Frankenhaeuser, B., Hodgkin, A. L.: The action of calcium on the electrical properties of squid axons. J. Physiol. (Lond.)137, 217–244 (1957).
Giebisch, G., Weidmann, S.: Membrane currents in mammalian ventricular heart muscle fibres using a “voltage-clamp” technique. Helv. physiol. pharmacol. Acta25, CR 189–190 (1967).
Haas, H. G., Kern, R.: Na inactivation and reactivation in cardiac muscle. Pflügers Arch.312, 28 (1969).
——: Einwächter, H. M.: Electrical activity and metabolism in cardiac tissue: An experimental and theoretical study. J. Membrane Biol.3, 180–209 (1970).
Hagiwara, S., Nakajima, S.: Differences in Na and Ca spikes as examined by application of tetrodotoxin, procaine and manganese ions. J. gen. Physiol.49, 793–806 (1966).
Hodgkin, A. L., Huxley, A. F.: Currents carried by sodium and potassium ions through the membrane of the giant axon of Loligo. J. Physiol. (Lond.)116, 449–472 (1952a).
——: The components of membrane conductance in the giant axon of Loligo. J. Physiol. (Lond.)116, 473–496 (1952b).
——: The dual effect of membrane potential on sodium conductance in the giant axon of Loligo. J. Physiol. (Lond.)116, 497–506 (1952c).
——: A quantitative description of membrane current and its application to conduction and excitation in nerve. J. Physiol. (Lond.)117, 500–544 (1952d).
Hoffman, B. F., Cranefield, P. F.: Electrophysiology of the heart. New York-Toronto-London: McGraw-Hill Book Company 1960.
Mascher, D., Peper, K.: Two components of inward current in myocardial muscle fibers. Pflügers Arch.307, 190–203 (1969).
Merideth, J., Mendez, C., Mueller, W. J., Moe, G. K.: Electrical excitability of atrioventricular nodal cells. Circulat. Res.23, 69–85 (1968).
Niedergerke, R., Orkand, R. K.: The dual effect of calcium on the action potential of the frog's heart. J. Physiol. (Lond.)184, 291–311 (1966).
Pillat, B.: Prolongation of the relative refractory period by drugs acting like quinidine; occurrence of propagated spikes in cardiac muscle. Helv. physiol. pharmacol. Acta25, 32–39 (1967).
Rougier, O., Vassort, G., Garnier, D., Gargouil, Y. M., Corabœuf, E.: Existence and role of a slow inward current during the frog atrial action potential. Pflügers Arch.308, 91–110 (1969).
——, Stämpfli, R.: Voltage clamp experiments on frog atrial heart muscle fibres with the sucrose gap technique. Pflügers Arch. ges. Physiol.301, 91–108 (1968).
Szekeres, L., Vaughan Williams, E. M.: Antifibrillatory action. J. Physiol. (Lond.)160, 470–482 (1962).
Tarr, M., Haas, H. G., Trank, J.: Effects of manganese and tetrodotoxin on two inward currents in cardiac muscle. Physiologist12, 371 (1969).
Weidmann, S.: The effect of the cardiac membrane potential on the rapid availability of the sodium-carrying system. J. Physiol. (Lond.)127, 213–224 (1955a).
—: Effects of calcium ions and local anaesthetics on electrical properties of Purkinje fibres. J. Physiol. (Lond.)129, 568–582 (1955b).
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This work was supported by the Stiftung Volkswagenwerk and by grants from USPHS (N. HE 12426) and Kansas Heart Association.
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Haas, H.G., Kern, R., Einwächter, H.M. et al. Kinetics of Na inactivation in frog atria. Pflugers Arch. 323, 141–157 (1971). https://doi.org/10.1007/BF00586445
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DOI: https://doi.org/10.1007/BF00586445