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

Abstract

SU-MMARY1. Uptake and release of radiophosphate were measured in desheathed rabbit vagus nerve.2. During incubation in Locke containing 0-2 mM-[32P]phosphate a slow labelling of water soluble compounds of the nerve was found; the labelling of the non water soluble compounds was much smaller. During washing with inactive Locke, the label was almost entirely released from the water soluble compounds; the radioactivity of these compounds was therefore used as the basis for the calculation of the efflux rate constants.3. The efflux of radiophosphate increased with increasing phosphate concentration of the washing fluid.4. A similar effect of external phosphate on the efflux of radiophosphate was seen when the phosphate concentration was suddenly changed. The rate constants were in 0 02 mM-phosphate PM29 x 10-m d-1, in 0-2 mM 1-95 x 10-3 min-I, and in 2 mm 3-21 x 10-3 min-' at 37 'C. After changing the external solution the efflux reached a new level with a time constant of about 9 mi.5. Addition of arsenate also increased the efflux of radiophosphate; on a molar basis the effect of arsenate was slightly smaller than the effect of phosphate. the ratio between the Na dependent effluxe8 in 2 and 0-2 mM-phosphate was approximately equal to the ratio between the Na dependent influxes in 2 and 0*2 mMphosphate.10. The efflux of 22Na had a rate constant of 0 050 min-' in Locke and 0x046 minin Tris-Locke.11. It is concluded that part of the efflux of phosphate is mediated by a 508 J. FERRERO AND OTHERS Na-dependent transport system; the system appears to be able to exchange phosphate between the inside and the outside and to mediate net movements of phosphate in both directions.

Role of potassium in the phosphate efflux from mammalian nerve fibers

“…More than 95% of the radioactivity was found in the inorganic phosphate fraction (maximal sensitivity of the method, Ferrero et al, 1978).…”

“…We have shown previously that the efflux of phosphate is considerably reduced when preparations are exposed to Na-free solution (Ferrero et al, 1978). In the next series of experiments, the effects of potassium were studied in Na-free solution.…”

“…In order to test whether extracellular K alters the intracellular phosphate content, the water-soluble phosphates of nerves were extracted and separated by column chromatography (Ferrero et al, 1978). For these experiments nerves were loaded with 32p, washed with Locke for 120 min and then for 30 rain with either Locke or K-free or K-rich Locke, and finally analyzed.…”

“…It may correspond to the phosphorylation of membrane phospholipids. A mathematical model of this system is developed and curves simulated by an analog computer are compared to the experimental results.Measurements of the membrane potential and the internal inorganic phosphate showed that the effect of K on the phosphate efflux could not be explained by changes in the membrane potential or in the internal phosphate pool.We have shown previously that a large proportion of the transmembrane fluxes of inorganic phosphate in nonmyelinated nerve fibers is mediated by a saturable Na-dependent mechanism (Armor et al, 1976;Ferrero et al, 1978). This mechanism is different from the phosphate transport in other tissues, e.g., erythrocytes (Rothstein, Cabantchick & Knauf, 1976), mitochondria (Banerjee et al, 1977) or Escherichia coli (Rosenberg, Gerdes & Harold, 1979).…”

Uptake of adenosine and release of adenine derivatives in mammalian non‐myelinated nerve fibres at rest and during activity

“…For the measurement of the efflux, the preparations were loaded with radioactivity by incubation in [2-3H]adenosine labelled solution with 01 M-adenosine during 2 hr. They were then mounted in the apparatus described by Ritchie & Straub (1975) Ferrero, Jirounek, Rouiller & Straub, 1978). In some experiments the effluent was analysed by thin-layer chromatography on silica gel plastic sheets as described by Shimizu, Creveling & Daly (1970).…”