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Prolonged post tetanic de polarization of frog rana pipiens dorsal root fibers

, : Prolonged post tetanic de polarization of frog rana pipiens dorsal root fibers. Neuroscience 9(1): 235-243

In the isolated frog spinal cord, tetanic stimulation of a dorsal root resulted in a sustained negative potential recorded from that root. This negative potential was followed by a large (5-12 mV) and slow (5-60 s) negative after-potential which persisted after the train of impulses and which was succeeded by a long-lasting positive potential. The negative after-potential was postulated to be largely a consequence of excess extracellular K+ accumulated during the tetanus, because the negative afterpotential and the extracellular [K+] measured with K+-sensitive microelectrodes were a function of the stimulating current, the stimulation frequency and the duration of the tetanus. Both measures were augmented by procedures which interfered with the clearance of K+ from the extracellular space (addition of dinitrophenol or ouabain, partial substitution of Li+ for Na+, elimination of K+ from the superfusate and cooling). The negative after-potential and the liberation of much of the excess extracellular K+ were reduced by increasing the superfusing divalent ion concentration with 4 mM Ca2+ or 50-100 .mu.M Mn2+. Both measures were augmented in low Ca2+-containing Ringer's solution. The results with low concentrations of Ca2+, Na+ and K+ and with high concentrations of Ca2+ indicate that the negative after-potential was not caused by a conductance increase for these cations. reduction of extracellular [Cl-] did not change the negative after-potential making it unlikely that this anion is a factor in its production. The negative after-potential was not mediated by GABA because its amplitude and duration were increased by the GABA antagonist picrotoxin and were reduced by pentobarbital which enhances the actions of GABA. Application of the excitatory amino acid antagonists DL-.alpha.-aminoadipic acid and glutamic acid diethylester eliminated the negative after-potential and markedly reduced the amount of K+ liberated by a tetanus. These results suggest that the K+ release that produces the negative after-potential may result from the action of an excitatory amino acid such as L-glutamate or L-aspartate either synaptically released or released from nonsynaptic regions of afferent fibers.

Accession: 006200222

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Related references

Davidoff, R.A.; Hackman, J.C., 1983: Prolonged 13 c+post-tetanic depolarization of frog dorsal root fibers. Neuroscience 9(1): 235-243

Lopez E., 1982: Post tetanic potentiation and inhibition in single fibers isolated from frog rana pipiens semitendinosus muscle. The twitch contractions of single fibers from the frog semitendinosus, innervated and denervated, were studied consecutively over a brief period (2-3 s) of conditioning stimulation (CS), at frequencies varying from 1-120/s. Twitch potentiation was...

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Bergman J., 1972: Contribution to the study of post tetanic hyper polarization of a bundle of nerve fibers of the frog. Comptes Rendus Hebdomadaires des Seances de l'Academie des Sciences Serie D Sciences Naturelles 274(8): 1172-1174

Bergmans J., 1969: Prolonged post tetanic hyper polarization induced in single nerve fibers by long lasting repetitive stimulation. Archives Internationales de Physiologie et de Biochimie 77(2): 321-323

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