Pflügers Archiv

, Volume 362, Issue 3, pp 209–218 | Cite as

Slow inward current and action potentials of papillary muscles under non-steady state conditions

  • Jiří Šimurda
  • Milena Šimurdova
  • Pavel Braveny
  • Josef Šumbera
Article

Summary

  1. 1.

    The relationship of the contractile response of cat papillary muscles and of the slow inward current, recorded under voltage clamp conditions (single sucrose gap), has been studied. The preparations were driven at a rate of 30 per min at 31° C. Both variables were recorded during a train of 7 identical clamp depolarizations (for 1 s from resting potential to −15 to +40 mV). The contractility increased severalfold and reached the steady state within 5–6 consecutive depolarizations.

     
  2. 2.

    The voltage-dependence of slow inward current was confirmed: maximum was found at depolarizations near 0 mV. On repetition of clamp pulses the slow current gradually diminished in amplitude and was more slowly activated and inactivated. The shift of the current-voltage curve indicated a decrease of the reversal potential.

     
  3. 3.

    Under non-steady state conditions the amplitude of the slow current was found to correlate closely with the magnitude of the contractile response at any given level of depolarization. The relation was linear with negative slope. The largest contractile response was not found at voltages which elicited maximum slow current.

     
  4. 4.

    The progressive decrease of the slow current during repetition of voltage clamp depolarizations is not significantly affected by inadequate time for recovery of slowly changing conductances, since it occurs also at stimulation frequency 15 per min and the slow current remains virtually unaltered after 20 s period of quiescence.

     
  5. 5.

    The course of total ionic current during phase 1 and 2 of action potential was reconstructed from a family of current curves obtained as a response to clamp depolarizations to various voltages, respecting the contractility-dependence of the current. The resulting course was correlated with the first derivative of action potential. A general conformity was ascertained.

     
  6. 6.

    The correlation of slow inward current with action potential configuration indicates that the rate of its activation determines the depth of the notch separating spike and plateau, its magnitude determines the voltage of the plateau phase and its rate of inactivation affects repolarization.

     
  7. 7.

    It is concluded that the described simultaneous changes of mechanical and electrical phenomena might be due to increased [Ca]i, which is responsible for more intense activation of the contractile proteins on the one hand, and decreased driving force of the slow inward current, carried by Ca ions, on the other.

     

Key words

Cat papillary muscle Action potential Slow inward current Contractility dependence 

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Copyright information

© Springer-Verlag 1976

Authors and Affiliations

  • Jiří Šimurda
    • 1
  • Milena Šimurdova
    • 1
  • Pavel Braveny
    • 2
  • Josef Šumbera
    • 3
  1. 1.Research Institute of Medical EngineeringBrno
  2. 2.IInd Department of MedicinePurkyně UniversityBrnoCzechoslovakia
  3. 3.Department of Physiology Medical FacultyPurkyně UniversityBrnoCzechoslovakia

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