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Pflügers Archiv

, Volume 323, Issue 2, pp 141–157 | Cite as

Kinetics of Na inactivation in frog atria

  • H. G. Haas
  • R. Kern
  • H. M. Einwächter
  • M. Tarr
Article

Summary

  1. 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.

     
  2. 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%.

     
  3. 3.

    During depolarizing clamps inactivation of Na current follows an approximately exponential time course with time constants between 1.5 and 8 msec.

     
  4. 4.

    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.

     
  5. 5.

    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.

     
  6. 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.

     
  7. 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.

     

Key-Words

Frog Atria Na Inactivation Sucrose-Gap Voltage Clamp Hodgkin-Huxley Equations 

Zusammenfassung

  1. 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.

     
  2. 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.

     
  3. 3.

    In depolarisierenden Klemmen verläuft die Inaktivierung des Na-Stroms angenähert exponentiell mit Zeitkonstanten zwischen 1,5 und 8 msec.

     
  4. 4.

    Die Rückbildung der Inaktivierung (Reaktivierung des Na-Systems) nach einer Repolarisation oder Hyperpolarisation verläuft mit Zeitkonstanten zwischen 100 und 600 msec.

     
  5. 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.

     
  6. 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.

     
  7. 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.

     

Schlüsselwörter

Froschvorhof Na-Inaktivierung Spannungsklemme Hodgkin-Huxley-Gleichungen 

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Copyright information

© Springer-Verlag 1971

Authors and Affiliations

  • H. G. Haas
    • 1
    • 2
  • R. Kern
    • 1
    • 2
  • H. M. Einwächter
    • 1
    • 2
  • M. Tarr
    • 1
    • 2
  1. 1.I. Physiologisches Institut der UniversitätHeidelbergGermany
  2. 2.Department of PhysiologyUniversity of Kansas Medical CenterKansas CityUSA

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