Abstract
1. The nodal currents of single myelinated nerve fibres were recorded under potential clamp conditions, and the effect of [Ca], [Na] and [K] in the external solution on some of the Na permeability properties were analysed. 2. [Ca], [Na] and [K] all affected the position of the steady-state Na inactivation (h) curve on the potential axis. The curve was displaced in positive direction by high ionic concentration. 3. The shift associated to different [Ca] was largest in low [Na] and [K]. Similarly the shift associated to different [Na] and [K] was largest in low [Ca]. 4. The maximum peak sodium permeability (max. peak - PNa) was affected by the [Ca], [Na] and [K]. It was greater in (i) low [Ca], (ii) high ([Na] + [K]) and (iii) high [Na]:[K] ratio. 5. The effect of [Ca] on peak - Na was mainly a consequence of a change in PNa (which is the value of PNa if activation were complete, m = 1, and inactivation fully removed, h = 1).
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