These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Extracellular potassium levels and axon excitability during repetitive action potentials in crayfish.
    Author: Smith DO.
    Journal: J Physiol; 1983 Mar; 336():143-57. PubMed ID: 6875904.
    Abstract:
    Changes in extracellular K+ levels were measured during repetitive stimulation of the excitor axon of the opener muscle of the crayfish walking leg. Mesaxon channels, through which K+ might diffuse away from the periaxonal ('Frankenhaeuser-Hodgkin') space, were examined in electron micrographs; they were seen every 2-10 micron along the axon, and their average (+/- S.D.) length and width were 3.0 (+/- 1.6) micron and 19.8 (+/- 8.9) nm, respectively. Intracellular recordings revealed a 40 ms after-depolarization following an action potential; this was attributed to elevated levels of extracellular K+. During stimulation at 50 Hz, this resulted in a depolarizing shift of the membrane potential between impulses; the average depolarization was 9.3 mV, which corresponds to a 4.3 mM increase in extracellular K+. Using K+-selective micro-electrodes, changes in extracellular K+ activity, delta aK, were measured at distances ranging from 10 to 50 micron from the axon; during 50 Hz stimulation, delta aK rose within 15 s to a maximum value of 1.1 mM which was maintained at a steady level in most preparations. Conduction failure occurred in several preparations after at least 90 s of stimulation; levels of delta aK were not abnormally high in these cases. Soaking the axon for at least 15 min in saline with extracellular K+ levels at least 18 mM above normal values was necessary to cause blockage in unstimulated nerves. Soaking the preparation for 30 min in 10(-3) M-ouabain resulted in a 48% increase in the maximum values of delta aK during 50 Hz stimulation. It is concluded that K+ accumulates extracellularly during axon stimulation and that the extent of this accumulation is reduced by active uptake mechanisms; however, this accumulation probably cannot directly block action potential conduction, for neither the magnitude nor the kinetics of K+ build-up approach values shown to reduce excitability.
    [Abstract] [Full Text] [Related] [New Search]