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

SUMMARY1. Influx of adenosine into rabbit non-myelinated nerve fibres was measured using [2-3H]adenosine. The uptake of radioactivity increased linearly with duration of incubation for up to 60 min and adenosine concentration up to 200 UM. The uptake at different adenosine concentrations showed a saturable component with a halfmaximal activation at 17-1 /M and a linear part.2. The radioactivity taken up was rapidly incorporated into AMP, ADP and ATP. Isotopic equilibrium between the nucleotides was achieved within 15 min.3. The uptake of 3H from 0-2 gM-adenosine was almost completely inhibited by addition of 200 gM-adenosine and to a similar extent by 200 /LM-tubercidin and AMP; a 70 % inhibition was found with ATP and ADP; a, , methylene-ADP had no effect.4. ATP, ADP and AMP added to the extracellular medium of a desheathed vagus were slowly hydrolysed.5. In preparations loaded with [2-3H]adenosine and then washed with adenosine and label-free solution there was a steady efflux of radioactivity amounting to 0 18 x 10-3/min. Addition of adenosine or tubercidin transiently increased the efflux. 6. Electrical stimulation caused an extra release of radioactivity. The extra fractional loss was 21-8 x 10-6/impulse in preparations that had rested for several hours; it decreased to 2-3 x 10-6/impulse when stimulation was applied after a 30 min rest.7. The radioactivity of the resting efflux and of the extra efflux after stimulation was found mostly in inosine and hypoxanthine; adenosine and adenine accounted for only 3 %, and the nucleotides for less than 1 % of the efflux.8. Adenosine added to the external medium of a desheathed nerve was slowly deaminated. 9. It is concluded that inosine and hypoxanthine found in the effluent from desheathed vagus nerve trunk result from release of these compounds from nerve fibres and not from extracellular breakdown of released ATP or adenosine.10. Electrical activity in non-myelinated nerve fibres of the nerve trunk thus causes the release of metabolites (inosine and hypoxanthine) together with small amounts of adenosine and adenine, while release of ATP and other nucleotides is almost completely absent.

supporting

confidence: 81%

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

Maire¹,

Medilanski²,

Straub³

1982

“…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). The present experiments describe the resting efflux in more detail, particularly the effects of phosphate and other anions and the dependence on the Na concentration.…”

Section: Introductionmentioning

confidence: 72%

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

Ferrero¹,

Jirounek²,

Rouiller³

et al. 1978

Self Cite

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.

“…During, and immediately after, activity the efflux of phosphate increases, as does the 02 consumption. The time courses of development, and subsequent decline, of these two responses are roughly parallel; and it has been proposed that both increases result from a common determining factor, namely, the increase in intracellular inorganic phosphate following the increased metabolic activity of the nerve as it extrudes the Na that had entered the nerve during the electrical activity (Ritchie & Straub, 1978, 1979.…”

Section: Introductionmentioning

confidence: 99%

Oxygen consumption and phosphate efflux in mammalian non‐myelinated nerve fibres.

Ritchie¹,

Straub²

1980

Self Cite

SUMMARY1. A comparison has been made between the efflux of labelled phosphate from the non-myelinated fibres of the desheathed rabbit vagus nerve at 37 TC and the corresponding 02 consumption at rest and during activity, and during a variety of experimental interventions.2. The resting rate constant of phosphate efflux was 2-61 x 10-3 min': electrical stimulation (10 sec-', 3 min) produced an extra fractional loss of 6-75 x 10-6 impulse-'.3. The corresponding resting 02 consumption was 0*484 m-mole. kg-1 min-' and the extra 02 consumption with electrical activity was 0-467 Emole . kg-1 impulse-'.4. Ouabain (100 /tM) produced a sustained depression (of about 40%) of the resting 02 consumption, accompanied by a transient fall (of about 14%) in the rate constant of phosphate efflux. 5. Na salicylate (10 mM) or Na arsenate (1 mM) produced a much larger increase in phosphate efflux than in resting 02 consumption.6. Changing the external phosphate concentration (between 0-02 and 2 mM), addition of acetylcholine (1.7 mM), and addition of lanthanum (20 ,/M) -all of which are known to affect markedly the phosphate efflux in rabbit non-myelinated fibreshad little or no effect on the resting 02 consumption or, where tested, on the extra 02 consumption with electrical stimulation. 7. Changing the external Ca concentration (between 0-09 and 9 mm) had only minor effects on the 02 consumption (resting and stimulated) and on the rate constant of resting phosphate efflux.8. It is concluded that although changes in metabolism of the nerve produce changes in the phosphate efflux expected on the basis of the concomitant changes in the internal concentration of inorganic phosphate, the converse is not true; and increases and decreases in the rate constant of phosphate efflux do not necessarily signal the corresponding metabolic changes.