Sodium-Dependent Transport of Orthophosphate in Nerve Fibres

Straub, R. W.; Ferrero, J; Jirounek, P.; Rouiller, M.; Salamin, A.

doi:10.1007/978-1-4613-4217-5_33

Cited by 8 publications

(2 citation statements)

References 10 publications

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“…The results of measurements at different sodium concentrations are summarized in Table 1. When sodium was replaced by lithium, the efflux also decreased. These effects of low-sodium solutions on garfish nerve are similar to those found in rabbit vagus nerve (Ferrero, Jirounek, Rouiller, Salamin & Straub, 1976;Straub, Ferrero, Jirounek, Rouiller & Salamin, 1977).…”

Section: Effect Of External Sodiumsupporting

confidence: 77%

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

Ritchie¹,

Straub²

1978

The Journal of Physiology

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SUMMARY1. The movements of labelled phosphate were measured in garfish olfactory and in rabbit vagus nerves at rest and during activity.2. In garfish olfactory nerve kept in solutions with 120 mM-sodium and 0-2 mmphosphate the fractional loss of 32p was 9-82 x 10-4 min1. Lowering the sodium concentration of the washing fluid decreased the efflux; lowering the phosphate produced a transient increase with subsequent return towards the efflux in 0-2 mMphosphate. 8. The extra efflux with stimulation seems to result predominantly from an increase in intracellular inorganic phosphate resulting from increased break-down of ATP after activity.

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Section: Effect Of External Sodiumsupporting

confidence: 77%

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

Ritchie¹,

Straub²

1978

The Journal of Physiology

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“…This difference indicates that some of the phosphate of the water-soluble extract does not contribute to the efflux. Moreover, the higher external phosphate concentration in this experiment (0.6 mM instead of 0.2 raM) contributes to an increased efflux (Straub et aL, 1977); temperature, 37 ~ phosphate ions and an opposite effect is expected from the depolarization in K-rich solution. Qualitatively, the effects of K on the phosphate fluxes could thus be explained by these changes in the membrane potential.…”

Section: A Metabolic Effects Of Potassiummentioning

confidence: 80%

Role of potassium in the phosphate efflux from mammalian nerve fibers

Jirounek¹,

Rouiller²,

Ferrero³

et al. 1980

J. Membrain Biol.

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Summary. The efflux of phosphate was measured in rabbit vagus nerve loaded with radiophosphate. The efflux was found to depend on the K concentration of the bathing solutions; increasing the K from 5.6 up to 150 mM produced a maximal lowering of 28% ; K-free solution produced a transient increase whose peak was 86% above the normal efflux. In the presence of Na, the K-free effect could be repeated; in Na-free solution, it was found only for the first application of the K-free solution. The phosphate efflux was not altered when K was replaced by Rb; replacement with Cs showed that this ion only partially mimics the effect of K.The results suggest that the transient increase in phosphate effiux is due to release of label from a K-dependent saturable binding site, which is distinct from the main intracellular pool. The binding site appears to be labeled from the inside by the Nadependent phosphate efflux previously described. 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).In the course of further investigations on the phosphate efflux, a transient release of phosphate was observed when the potassium of the incubation solution was withdrawn. Conversely, when the potassium was increased, the efflux of phosphate was diminished. In the present study, we have analyzed these phenomena in more detail. Our results suggest that the phosphate released in the absence of K originates from a specific K-dependent phosphate binding site. Materials and MethodsDesheathed rabbit vagus nerves were mounted in a polyethylene tube which was perfused with 32p-phosphate Locke for 150 rain at 37 ~ The preparation then was washed with inactive Locke solution, and the effluent was collected and counted. At the end of the experiment the preparation was homogenized in 0.1 g triethanolamine buffer (pH 8). The homogenate was mixed with chloroform, centrifuged at 3,000 xg for 15 min and the activity of the water-soluble fraction was then counted. These counts were used for the calculation of the efflux rate constant. The composition of the Locke was (raM): 154 NaC1, 5.6 KC1, 0.9 CaC12, 0.5 MgCI2, 5 glucose, 0.2 Na2HPO4-NaH2PO4, 1 Tris. Potassium isethionate (Eastman-Kodak) was added to prepare K-rich Locke. In Na-free solutions, sodium wa...

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Evidence for monovalent phosphate transport in Ehrlich ascites tumor cells

Bowen

Levinson

1983

Journal Cellular Physiology

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In an effort to determine whether the Na+-dependent Pi transport system of Ehrlich ascites tumor cells exhibits specificity for H2PO4- or HPO4(-2), Pi fluxes were determined by measuring 32Pi-Pi self-exchange. Three experimental approaches were employed. First, the effect of pH on steady-state Pi transport at 0.5 and 5 mM was studied. Second, the relationship between Pi transport and Pi concentration (0.25-9.2 mM) at pH 5.6 and 7.9 was determined. Third, the dependence of Pi transport on [H2PO4-] (0.05-4.2 mM) at constant [HPO4(-2)] (0.5 mM), and the converse, [HPO4(-2)] (0.06-4.5 mM) at constant [H2PO4-] (0.5 mM), was evaluated. Ks (apparent half-saturation constant) and Jmax (maximal transport rate) were calculated by two methods: weighted linear regression (WLR) and a nonparametric procedure. The dependence of Pi flux on pH indicates that optimum transport occurs at pH 6.9. Pi transport decreases as pH is reduced when extracellular Pi is either 0.5 or 5 mM. However, at pH 7.9, Pi flux is reduced only in 0.5 mM Pi. At pH 5.6, H2PO4- comprises 93% of the total Pi present, and the calculated Ks is 0.055 +/- 0.026 mM (WLR). This is the same as the Ks determined from the initial phase of the flux vs. [H2PO4-] relationship (0.056 +/- 0.020 mM). However, at pH 7.9 (where 94% of Pi is HPO4(-2)), the measured Ks is 0.58 +/- 0.11 mM (WLR), which is ten times higher than at pH 5.6. This value is also five times greater than the Ks calculated from the flux vs. [HPO4(-20)] curve (0.106 +/- 0.16 mM). Kinetic parameters calculated by the nonparametric method, though somewhat different, gave similar relative results. Taken together, these results support two conclusions: (1) H2PO4- is the substrate for the Na+-dependent Pi transport system of the Ehrlich cell, and (2) H+ can inhibit Pi transport.

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Sodium-Dependent Transport of Orthophosphate in Nerve Fibres

Cited by 8 publications

References 10 publications

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

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

Role of potassium in the phosphate efflux from mammalian nerve fibers

Evidence for monovalent phosphate transport in Ehrlich ascites tumor cells

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