CONDUCTION OF NERVOUS IMPULSES IN NaCl-DEFICIENT MEDIA

Uehara, Yoko

doi:10.2170/jjphysiol.8.282

Cited by 7 publications

(2 citation statements)

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“…A preliminary report of some of the results has been made to the Physiological Society (Nathan & Sears, 1960b); since that time, similar findings by Uehara (1958Uehara ( , 1960 have come to our notice. Working on 376 P. W. NATHAN AND T. A. SEARS single myelinated fibres of the frog, she has also found that fibres of different sizes are blocked by different critical concentrations both of sodium ions and of local anaesthetics.…”

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“…It is evident that if small fibres have a lower safety factor than these large fibres, a lesser reduction in the nodal action current will cause conduction to fail in them. We have been unable to find any published figures for the safety factor of small fibres.A preliminary report of some of the results has been made to the Physiological Society (Nathan & Sears, 1960b); since that time, similar findings by Uehara (1958Uehara ( , 1960 …”

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Differential nerve block by sodium‐free and sodium‐deficient solutions

Nathan¹,

Sears²

1962

The Journal of Physiology

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In the present paper the results of lowering the concentration of sodium ions in the external medium of myelinated and non-myelinated fibres of the cat's spinal roots are described. These experiments were conducted in a similar manner to those of our previous study (Nathan & Sears, 1961) on the effects of local anaesthetics. It has been found that with sodium-freg solutions the small fibres are blocked more rapidly than large fibres; thus there is a differential rate of blocking, and the results resemble those obtained with anaesthetic solutions in which the concentration is at least critical for all fibres present. With sodium-deficient solutions, absolute differential blocking has been obtained, there being critical concentrations of sodium that block conduction in the smaller fibres while allowing that of the larger fibres to continue; in this respect these results resemble those obtained with critical concentrations of local anaesthetics.In our previous paper we put forward the suggestion that absolute differential blocking is due to the safety factor of small myelinated fibres being lower than that of large myelinated fibres. According to Tasaki's (1953) measurements, using the bridge-insulator method on isolated single myelinated fibres of the toad, the safety factor, defined as the ratio of the nodal action current to the nodal rheobasic current, is between 5 and 7.This implies that if the nodal action current is experimentally reduced to between 15 and 20 % of its normal value, conduction will fail. It is evident that if small fibres have a lower safety factor than these large fibres, a lesser reduction in the nodal action current will cause conduction to fail in them. We have been unable to find any published figures for the safety factor of small fibres.A preliminary report of some of the results has been made to the Physiological Society (Nathan & Sears, 1960b); since that time, similar findings by Uehara (1958Uehara ( , 1960 METHODSAll experiments were performed under the same conditions as those previously used for investigating the differential action of local anaesthetics; these methods were described in our previous papers (Nathan & Sears, 1960a, 1961. The experiments were performed on seventeen cats anaesthetized with Nembutal (Pentobarbitone, Abbott Laboratories; 35-40 mg/kg), given by intraperitoneal injection.In brief, solutions deficient in sodium were applied to nerve roots in a Perspex chamber of internal diameter 8 mm and a cubic capacity of 1 ml. The recording was made from a stretch of nerve fibres bathed in a solution containing the normal amount of sodium, the effects of sodium-deficiency being confined to the length of the nerve fibres in the chamber. Control experiments showed that the reduction in amplitude of the compound action potential was not due to diffusion of sodium ions away from the nerve on the recording electrodes, but was due only to a reduction in the number of fibres conducting impulses through the chamber. Further, as a precautionary measure, Krebs-Henseleit soluti...

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confidence: 56%

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confidence: 76%