Sodium‐dependent influx of orthophosphate in mammalian non‐myelinated nerve.

Abstract

B. ANNER AND OTHERS 10. The influx of phosphate was calculated for different external phosphate concentrations using the rate of uptake of radiophosphate measured 45 min after the application of isotope and the corresponding efflux rate coefficients and the intracellular specific activities of the labelled compounds.11. A correction was also introduced for diffusion, using the 'limited biophase model'.12. The Na-sensitive influx, i.e. the difference between influx in Locke and influx in choline-Locke, showed saturation kinetics.13. A Lineweaver-Burk plot for Na-sensitive uncorrected influxes gave a vmax of 16-7 #tmole/kg wet wt. min and an apparent Km of 0-42 mM;for the corrected fluxes these values were 18-2 and 0-36. 14. It is concluded that a large part of phosphate influx and some of the phosphate efflux is mediated by a specific Na-dependent phosphate transport system.15. This system seems to be present also in other types of nervous tissues and probably in many types of animal cells.

Efflux of inorganic phosphate from mammalian non‐myelinated nerve fibres.

“…Changes in internal phosphate, however, are unlikely to occur in these conditions, since previous experiments showed that variations of external phosphate do not appreciably alter the internal phosphate concentration (Anner et al 1975). This is understandable, since both influx and efflux increase with increasing extracellular phosphate concentration; further, both fluxes are small compared to the internal phosphate pool (see Anner et al 1976). Since the internal phosphate does not change appreciably, the present results suggest that the efflux is stimulated by external phosphate ions.…”

“…The techniques used were similar to those of previous experiments (Anner et al 1975(Anner et al , 1976. In brief, for measuring the influx, or for loading the tissue with radiophosphate, a desheathed cervical vagus nerve of a rabbit was mounted in a narrow polyethylene tube that was perfused with Locke or modified Locke.…”

“…Other experiments showed that there is a slew release of inorganic phosphate from these nerve fibres (Anner et al 1976). The efflux decreases when the preparations are kept in Na-free solutions; on the other hand, an increased release of phosphate is found during electrical activity (Ritchie & Straub, 1978).…”

“…Further it was found that the influx can be divided into a linear and a saturable term and that the saturable influx is dependent on the presence of sodium ions (Anner, Ferrero, Jirounek, Jones, Salamin & Straub, 1976). In Locke the apparent Km for the effect of external phosphate amounts to 0*38 mm, while preliminary experiments suggest that the Km of Na is about 20 mm, in the presence of 0-2 mM-phosphate, and that sodium acts by increasing the maximal rate of phosphate influx rather than the affinity of the transport system for phosphate (Straub, Ferrero, Jirounek, Rouiller & Salamin, 1977).…”

Increase in efflux of inorganic phosphate during electrical activity in small non‐myelinated nerve fibres.

“…Chromatography of the efflux has shown that in resting vagus nerve the radiophosphate is almost entirely found in the inorganic fraction (Anner et al 1976). During activity the inorganic phosphate in the nerve increases (Baker, 1965;Chmouliovsky et al 1969;McDougal & Osborn, 1976), and ATP and CrP are lowered: there is thus no reason to assume that the extra efflux during activity is not mostly released from the inorganic pool.…”