title: Slow action of Ca on myelinated nerve fibres of Xenopus laevis.
abstract: Single myelinated nerve fibres were isolated and the nodal currents were recorded with potential clamp technique. Rapid solution changes were performed by use of a recording chamber so shaped that it had a minimal dead space. A volume ten times larger than the dead space flowed past the node within about 20 ms. The half-time of the change in Na current (INa)amplitude associated with changes between solutions of different [Na]:s was 100-150 ms, whereas the half-time of the change in INa associated with changes between solutions of different [Ca]:s was 200-300 ms. The external [Ca] affects INa through its action on the Na permeability properties of the nodal membrane. The difference in rate of effect between changes in [Na] and [Ca] was also noticeable when simultaneous changes were performed. These findings are discussed with regard to the properties of the nodal gap.
mesh_terms: D000818:Animals; D001369:Axons / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects; D005071:Evoked Potentials / Q000187:drug effects; D008722:Methods; D009413:Nerve Fibers, Myelinated / Q000187:drug effects*; D011901:Ranvier's Nodes / Q000187:drug effects*; D012964:Sodium / Q000494:pharmacology; D014981:Xenopus
chemical_list: D012964:Sodium; D002118:Calcium