The ionic content of mammalian non-myelinated nerve fibres and its alteration as a result of electrical activity

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Abstract
The ionic content, and fibre water, of rabbit desheathed vagus nerves at rest and after activity in various modified Locke solutions were studied. In normal Locke solution the intracellular Na amounted to 86.1 [mu]mole/g dry, and the intracellular K 186.0 [mu]mole/g dry. Since the fiber water amounted to 1.124 g/g dry the intracellular sodium and K concentrations were 76.6 and 165.5 m-mole/kg fiber water, respectively. In K-free Locke solution the intracellular Na and K concentrations were 111.0 and 121.7 m-mole/kg, respectively. The intracellular chloride concentration was 40.5 m-mole/kg. In normal Locke solution, a brief period of stimulation followed by a 10 min recovery period produced no significant change in the intracellular contents of K, Na, or water. However, in chloride-Locke solution from which the K had been omitted, or to which ouabain (1 mM) had been added, stimulation caused a loss of K per impulse of about 20 p-mole/mg dry, i.e. about 4 p-mole/mg wet. A similar loss was found in isethionate-Locke solution that was K-free. There was no significant change in any of the other quantities measured (K, chloride, and fiber water). The efflux of radioactively labelled K was measured in K-free Locke solution at rest (kr) and during activity (ks). At 24[degree]C, kr was 0.0084 min-1 and ks was 0.000178 impulse"!. When the chloride of Locke solution was replaced by isethionate there was an increase in both kr (about 12%) and kg (about 21%). Ouabain (1 mM) increased ks (by about 70%). This increase seemed to be independent of whether the anion present was chloride or isethionate. These results seem to indicate that the electrogenicity of the pump plays a relatively small role in maintaining the ionic balance in mammalian C fibers.