ISSN:
1432-2013
Keywords:
Node of Ranvier
;
Ionic Currents
;
Scorpion Venom
;
Calcium Ions
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary Voltage clamp experiments were done on myelinated nerve fibres of Xenopus laevis to study the effect of calcium on the ionic currents of the nodal membrane treated with scorpion venom. Increasing the calcium concentration of the medium from 1.8 to 7.2 mM produced the following changes of the sodium and potassium permeabilities,P Na andP K: a) The incomplete sodium inactivation, which is typical for nodes of Ranvier treated with scorpion venom, is abolished. The curves relatingm ∞ and τ m to membrane potential are shifted by 8–10 mV towards larger depolarizations.P Na and the time constants of the fast and slow components of the sodium inactivation remain practically unchanged. b) The maximum potassium permeability,P K, which is reduced by scorpion venom to 45% of the value observed in the normal node, increases to 68% by addition of calcium ions; τ n is unchanged. These effects of calcium ions on the ionic permeabilities explain the shortening of the extremely prolonged action potential and the inhibition of spontaneous activity observed in nodes of Ranvier poisoned with scorpion venom.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00586041
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