The Journal of Membrane Biology

, Volume 103, Issue 3, pp 283–291 | Cite as

Predominance of poorly reopening single Na+ channels and lack of slow Na+ inactivation in neonatal cardiocytes

  • M. Kohlhardt
  • H. Fichtner
  • U. Fröbe


Elementary Na+ currents through single cardiac Na+ channels were recorded at −50 mV in cell-attached patches from neonatal rat cardiocytes kept at holding potentials between −100 and −120 mV.

Na+ channel activity may occur as burst-like, closely-timed repetitive openings with shut times close to 0.5–0.6 msec, indicating that an individual Na+ channel may reopen several times during step depolarization. A systematic quantiative analysis in 19 cell-attached patches showed that reopening may be quite differently pronounced. The majority, namely 16 patches, contained Na+ channels with a low tendency to reopen. This was evidenced from the average value for the mean number of openings per sequence, 2.5. Strikingly different results were obtained in a second group of three patches. Here, a mean number of openings per sequence of 3.42, 3.72, and 5.68 was found. Ensemble averages from the latter group of patches revealed macroscopic Na+ currents with a biexponential decay phase. Reconstructed Na+ currents from patches with poorly reopening Na+ channels were devoid of a slow decay component. This strongly suggests that reopening may be causally related to slow Na+ inactivation. Poorly pronounced reopening and, consequently, the lack of slow Na+ inactivation could be characteristic features of neonatal cardiac Na+ channels.

Key Words

slow Na+ inactivation Na+ channel kinetics reopening neonatal cardiocytes 


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Copyright information

© Springer-Verlag New York Inc 1988

Authors and Affiliations

  • M. Kohlhardt
    • 1
  • H. Fichtner
    • 1
  • U. Fröbe
    • 1
  1. 1.Physiological InstituteUniversity of FreiburgFreiburg/Br.West Germany

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