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. 1966 May;184(2):335–352. doi: 10.1113/jphysiol.1966.sp007918

The origin of the post-tetanic hyperpolarization of mammalian motor nerve terminals

P W Gage, J I Hubbard
PMCID: PMC1357564  PMID: 5921834

Abstract

1. Motor nerve terminals in magnesium-poisoned rat hemidiaphragm-phrenic nerve preparations in vitro were stimulated with short depolarizing pulses of approximately threshold strength and the evoked antidromic responses recorded from the phrenic nerve. The percentage of these 1/sec or 0·5/sec stimuli to which there was no antidromic response was used as a quantitative measure of the terminal excitability. After standard tetanic stimulation (1000 impulses at 100/sec) the excitability of the terminals was depressed for an average duration of 60-70 sec, during most of which time no antidromic responses to stimuli of pretetanic intensity were recorded. There was no significant interaction between stimuli to the terminals at rates of 1 or 0·5/sec.

2. Potassium-free solutions at first increased, then decreased, the post-tetanic depression of excitability. Raising [K]o threefold (15 mM) abolished the post-tetanic depression and often converted it to an exaltation of excitability.

3. Polarizing currents were applied to the terminals with a second electrode. Depolarizing currents increased, while hyperpolarizing currents decreased, the post-tetanic depression of excitability.

4. In solutions with 70% of the normal NaCl content replaced by sucrose, the post-tetanic depression of excitability was reversibly prolonged.

5. In the presence of 7·7 × 10-6 M digoxin or 0·42 mM ouabain there was a small reversible reduction of post-tetanic excitability.

6. After exposure to solutions containing no glucose or to solutions containing 3-5 mM sodium azide the excitability of the terminals was not altered by the tetanus. After washing with the control solution, post-tetanic depression of excitability returned. Antimycin-A (1·8 × 10-6 M) had little or no effect upon post-tetanic excitability.

7. It was concluded that the post-tetanic depression of excitability reflected hyperpolarization of the terminals and that this hyperpolarization was caused by a shift of the membrane potential towards the potassium equilibrium potential because of an increase in potassium permeability.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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