Sustained spontaneous activity of ranvier nodes induced by the combined actions of TEA and lack of calcium

Claude Bergmann, Wolfgang Nonner, Robert Stämpfli

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Abstract

Superfusion of a Ranvier node of r. esculenta and xenopus l. with Ringer's of reduced Ca++-content (0.05 to 0.1 mM/l) containing 5 mM/l TEA, induced spontaneous activity for more than 30 min. The frequency of discharge at beginning of superfusion was 192±39/sec. It declined within 30 to 60 sec to a steady value of 76±26/sec. Such membranes were submitted to voltage clamp analysis: Depolarisations between V=0 and 20 mV produced initial, between 0 and 10 mV steady state inward currents. This reversal of steady state currents compared to normal membranes is due to enhanced Na+-permeability (lack of Ca++) and to reduced K+-permeability (action of TEA). Analysis of the sodium system revealed (a) shift of the m (V) curve by 10 mV to smaller depolarizations (b) shift of the h (V) curve in same direction by 5 mV (c) little change of time constants τm and τk. The product m2h near the resting potential differs from zero. Spontaneous activity can thus be explained by the following cycle: After repolarization of the spike the nearly abolished sodium permeability grows toward its steady state value (h→h, m≈m). Accordingly the sodium inward current increases with the evolution of h and produces a depolarization (pacemaker potential) which by the early rise of the variable m becomes regenerative and leads to the next spike.

Original languageEnglish (US)
Pages (from-to)24-37
Number of pages14
JournalPflügers Archiv European Journal of Physiology
Volume302
Issue number1
DOIs
StatePublished - Mar 1968

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Keywords

  • Calcium Lack
  • Ranvier Node
  • Spontaneous Activity
  • TEA
  • Voltage Clamp

ASJC Scopus subject areas

  • Physiology

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