The influx of orthophosphate into squid giant axons

Abstract

1. The influx of 32P, applied externally as orthophosphate, into the axoplasm of squid giant axons has been studied. 2. An average orthophosphate influx of 20·9 f‐mole/cm2.sec is obtained if the 32P found in the axoplasm is assumed to be indicative of orthophosphate which has crossed the axolemma. 3. The influx does not show very much dependence on external orthophosphate concentration in the range 0·02–0·5 m M. 4. The influx is reduced by cyanide, 2,4‐dinitrophenol, ouabain and by the absence of external potassium. 5. The 32P appears to arrive in the axoplasm as orthophosphate. 6. It is concluded that there is an inward movement of orthophosphate into the axons which is mediated by an active transport process and that this may have some connexion with the active transport of sodium and potassium.

Phosphate fluxes in single muscle fibres of the spider crab, Maia squinado.

“…2. This contrasts with the inhibitory effect of ouabain on 32Pl influx into the squid giant axon (Caldwell & Lowe, 1970) and indicates that the efflux of 32p from Maia muscle fibres is not directly associated with the operation of the sodium-potassium pump. …”

“…At the end of each efflux experiment a piece of muscle fibre about 1-1-5 cm long and weighing 10-20 mg was cut from the centre of the cannulated fibre, frozen in solid C02/acetone and extracted with 5% (w/v) trichloroacetic acid as described by Caldwell (1953). A measured proportion of the soluble extract was fractionated by paper chromatography as described by Caldwell & Lowe (1970) and both radioactivity and total phosphate were measured in the areas of the chromatogram corresponding to orthophosphate, arginine phosphate and ATP.…”

“…C. CALDWELL AND A. G. LOWE 1970) indicating that the 32p moves across the membrane as orthophosphate. It seems therefore that orthophosphate is the main form in which phosphorus moves into and out of the cell across the membrane.…”

Glycine fluxes in squid giant axons.

“…7 shows that when the sodium in artificial sea water was replaced by choline P. C. CALD WELL AND T. J. LEA fluxes was carried out on the uptake of 32P-labelled orthophosphate. The pair axon method was used as in a previous study (Caldwell & Lowe, 1970). The results, given in Table 5, show that the orthophosphate uptake is greatly reduced when Na+ is replaced by choline or Li+, and that in this orthophosphate uptake in squid axons is similar to that in rabbit vagus nerve (Anner, Ferrero, Jirounek & Straub, 1975).…”

“…The first was essentially the extrusion method first used by Bear, Schmitt & Young (1937). It has recently been used for the study of orthophosphate uptake (Caldwell & Lowe, 1970). Uncleaned pair axons from the same animal were tied off at each end and immersed in artificial sea waters (ASWs) containing 14C-labelled amino acids (0.05 1sC ml.-').…”