Kinetics of Ion Movement in the Squid Giant Axon

Abstract

The loss of Na22, K42, and Cl36 from single giant axons of the squid, Loligo pealii, following exposure to an artificial sea water containing these radioisotopes, occurs in two stages, an initial rapid one followed by an exponential decline. The time constants of the latter stage for the 3 ion species are, respectively, 290, 200, and 175 minutes. The outflux of sodium is depressed while that of potassium is accelerated in the absence of oxygen; the emergence of potassium is slowed by cocaine, while that of sodium is unaffected. One cm. ends of the axons take up about twice as much radiosodium as the central segment; this difference in activity is largely preserved during exposure to inactive solution. Such marked differences are not observed with radiopotassium. From the experimental data estimates are given of the influxes and outfluxes of the individual ions. The kinetics of outflux suggests a cortical layer of measureable thickness which contains the ions in different proportions from those in the medium and which governs the rate of emergence of these ions from the axon as though it contained very few but large (relative to ion dimensions) pores.

Cation movements in perfused giant axons

“…Shanes & Berman (1955) found that the Na influx averaged 63 p-mole/cm2 . sec in L. pealii; Caldwell et al 214 T. 1.…”

“…The sodium influx into the intact giant axons of squidhas been measured by a number of workers (Shanes & Berman, 1955;Caldwell, Hodgkin, Keynes & Shaw, 1960); the flux is insensitive to cyanide and appears to be mainly a passive flux or leak. In the present work the influx of sodium into perfused fibres (Baker, Hodgkin & Shaw, 1962a) has been studied with the object of determining how much greater the leakage is into these fibres due to the manipulative treatment they have undergone.…”

The permeability of the squid giant axon to radioactive potassium and chloride ions

“…sec. Shanes & Berman (1955) determined the resting fluxes of labelled sodium, potassium and chloride in axons from Loligo pealii, and arrived at the following values in pmole/cm2. sec: Na influx 63, efflux 33; K influx 42, efflux 370; Cl influx 14, efflux 87.…”

“…The difficulty was eventually avoided by making measurements on extruded axoplasm, as described elsewhere (Caldwell et al 1960a, b), but not until a number of experiments had been done on intact axons. The complications encountered have some interest in their own right, and also have a bearing on the results reported by Shanes & Berman (1955). The purpose of this paper is to give a brief account of the preliminary influx determinations, and of a few experiments on the K efflux from axons into which 42K had been injected.…”

Studies on the internal pH of large muscle and nerve fibres

“…Calculations by means of the Henderson-Hasselbalch equation suggest that roughly 10-8 moles of hydrogen ions would have to pass into a volume of axoplasm of 1-25 x 10-2 cm3 across the 1 cm2 of membrane surrounding it, in order to decrease the pH by 01 of a pH unit. Shanes & Berman (1955) give a figure of 42 x 10-12 mole/cm2/sec for the influx of potassium across the membrane of the giant axon of the squid Loltigo pealii. If the ease with which hydrogen ions penetrate through the membranes of squid axons were similar to that for potassium ions, the actual influx of hydrogen ion for an external pH of 6-0 would be about 6 x 1o-5 of that for potassium, i.e.…”