Pflügers Archiv

, Volume 410, Issue 3, pp 326–334 | Cite as

Tension activation and relaxation in frog atrial fibres

Evidence for direct effects of divalent cations (Ca2+, Sr2+, Ba2+) on contractile proteins and Na−Ca exchange
  • Daniel Potreau
  • Sylvain Richard
  • Joel Nargeot
  • Guy Raymond
Excitable Tissues and Central Nervous Physiology


The effect of alkali-earth cations (Ca2+, Sr2+, Ba2+) on the excitation-contraction coupling events of the frog atrial fibres were studied using a double mannitol gap voltage clamp technique coupled with a mechano-electric transducer. Photoremoval of the suppressive effect of nifedipine on the calcium channels allowed to obtain rapid transient Ca2+, Sr2+ or Ba2+ ions current jumps. The effect on the amplitude of the associated contraction was proportional to the current jumps. These results together with portional to the current jumps. These results together with the correlation established between the estimated increase in the internal concentration of divalent cations and the amplitude of the phasic tension suggest that the essential source of divalent cations for activation of contraction is the extracellular space. Also Ba2+ ions reduced the tonic tension and strongly slowed the relaxation of the phasic component whereas Sr2+ exhibited smaller effects. Sr2+ ions could be more efficient than Ba2+ ions in substituting for Ca2+ ions in the Na+−Ca2+ exchange mechanism known to regulate these two mechanical events. The conclusions are that the order of effectiveness of these ions (Ca2+>Sr2+>Ba2+) is the same with regard to transarcolemmal exchange for Na+ ions, presumed uptake by a “second relaxing system”, activation of contraction, and inactivation of the slow inward current.

Key words

Excitation-Contraction Coupling Frog heart Alkali-earth cations Photolabile nifedipine Voltage-clamp 


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Copyright information

© Springer-Verlag 1987

Authors and Affiliations

  • Daniel Potreau
    • 1
  • Sylvain Richard
    • 2
  • Joel Nargeot
    • 2
  • Guy Raymond
    • 1
  1. 1.Laboratoire de Physiologie Générale, CNRS UA 290, Faculté des SciencesUniversité de PoitiersPoitiers CedexFrance
  2. 2.Centre de Recherches de Biochimie macromoléculaireCNRS LP 8402MontpellierFrance

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