The effects of @entity973 and XXXX ions on normal and demyelinated @entity1 nerve fibres.

@entity1 @entity1041 @entity17 @entity35 @entity5128 @entity7394 @entity974 @entity972 @entity973
1. @entity973 ( @entity974 ) and @entity5128 ions ( @entity1041 ), which block voltage-dependent @entity972 channels in other nerve membranes, have been used to study nerve conduction in fibres of normal @entity35 spinal roots and those demyelinated with @entity7394 toxin. The pharmacological actions have been compared with those of temperature. 2. Both @entity1041 and @entity974 increased the amplitude and duration of the monophasically recorded compound action potentials of non-myelinated fibres in normal @entity35 dorsal roots. Enhancement of the action potential amplitude by @entity974 was maximal near 1 mM, and was not readily reversed by washing. At concentrations up to 50 mM the action of @entity1041 was weaker and reversible. 3. In normal dorsal and ventral roots @entity1041 (20 mM) and @entity974 (5 mM) had only a mildly depressant action on the compound action potentials of myelinated fibres. Whereas the slight reduction in peak amplitude and increase in width was also found in a single fibres treated with @entity1041 , none was discerned in single fibres exposed to @entity974 over a wide temperature range. 4. It is concluded that voltage-dependent @entity972 channels occur in significant numbers in @entity1 non-myelinated fibres, but not at nodes of Ranvier. 5. Spinal roots previously treated with @entity7394 toxin to cause @entity17 were studied by longitudinal current analysis. Fibres affected by @entity7394 toxin had a late phase of outward current, either restricted to nodes or, in the case of continuous conduction, distributed along internodes, and this outward current was specifically blocked by @entity974 . 6. Both @entity974 and @entity1041 increased the temperature at which conduction block occurred in most single demyelinated fibres, so that in some cases fibres blocked at physiological temperatures were enabled to conduct. @entity974 was more potent than @entity1041 , but less consistent in its effect. 7. It is concluded that @entity972 channels are present at widened nodes and in internodal axolemma exposed by @entity17 . Their presence enables @entity1041 and @entity974 to overcome conduction block in some @entity17 .
