The distribution of Na and K in cat nerves

Abstract

Ever since the first full statement of the membrane theory (Bernstein, 1912) it has been widely believed that the mechanism of nervous conduction depends upon certain important differences between the concentrations of electrolytes inside and outside the nerve fibre. Bernstein had no evidence on this point and he relied for his argument on what evidence was available from analyses of muscle. We now know much about the composition of the intracellular fluid of invertebrate nerves (e.g. Lewis, 1952) and one analysis has been made of the electrolyte distribution in frog nerves (Fenn, Cobb, Hegnauer & Marsh, 1934). No study of the distribution of electrolytes in mammalian nerves, however, is apparently available.Estimations of the total content of Na, K and Cl in various mammalian (1954): Na and K. The information to be derived from these values is unfortunately greatly limited by complete uncertainty about the relative proportions of intra-and extracellular fluid and the relative proportions of total intra-and extracellular Na, K, or Cl. The present paper is an analysis of the distribution of Na, K and Cl in cat nerves, based upon: (a) a comparison of the total Na, K and Cl contents of intact nerve trunks and desheathed nerve bundles; (b) studies of the diffusion of Na from desheathed nerve bundles; (c) a direct estimate of the intracellular space obtained from photomicrographs. METHODSAnimals. Most of the nerves analysed were from cats. A small number of nerves from rabbits, dogs and monkeys were also studied for comparison; the only estimations made, however, were of the total Na and K.The majority of the nerves were removed from cats which were in good condition, with their circulation intact, in the course of experiments under general anaesthesia, or in some cases, after * Beit Memorial Research Fellow.

After‐potentials in mam‐malian non‐myelinated nerve fibres

“…A single impulse would therefore increase the sodium concentration by 2 mm in the smallest fibres of 0.1 it diameter (Gasser, 1955(Gasser, , 1956, and by 0-2 mm in the larger fibres which have a diameter of 1 U. The normal sodium concentration in mammalian C fibres is not known, but in mammalian myelinated fibres, Krnjevic (1955) found a sodium concentration of 40 mm. This value might be too high, but even with this value one impulse would still increase the sodium concentration by 5 % in the smallest and by 0 5 % in the largest C fibres.…”

cAMP and forskolin decrease gamma-aminobutyric acid-gated chloride flux in rat brain synaptoneurosomes.

“…cAMP-dependent phosphorylation of the nicotinic receptor-gated cation channel promotes receptor desensitization (33,37). Desensitization of the GABAA receptor has been demonstrated in a variety of preparations (38)(39)(40)(41), including the synaptoneurosome preparation (15,(42)(43)(44)(45). The loss in GABA receptor function associated with desensitization may lead to increased neuronal excitability and the development of seizures (38,40,46,47).…”

The rate of exchange of 24Na in cat nerves

“…V/A is to be taken as 2-1 x 10-4 cm and C, =41 x 10-6 mole/c.c. (Krnjevic, 1955). From these figures M = 3-75 x 10-12 mole/cm2.sec.…”

“…It is known that all the swelling in desheathed nerves takes place in the interstitial tissue (Lorente de N6, 1952;Shanes, 1953); therefore the extracellular water content of the desheathed nerve must increase from 43 % of the total water (Krnjevic, 1955) to about 62 % after 3 hr in Tyrode solution. From these figures and the values of the K concentration (32-4 m-mole/kg nerve) and water content (74-8%) of the nerve it can easily be shown that the intracellular K concentration must have been reduced from a normal level of about 180 (Krnjevi6, 1955) to about 110 m-mole/kg water.…”