No abstract

In a previous paper (Caldwell, 1954) a form of the glass electrode suitable for insertion into large muscle and nerve fibres was described, together with an account of some determinations with the electrode of the internal pH of the leg muscle fibres of the crab Carcinus maenas. In this paper more extensive studies of internal pH are presented. These comprise an investigation of the internal pH of the leg muscle fibres of C. maenas under a wide variety of conditions, and similar but less complete investigations of the internal pH of the leg muscle fibres of the crab Maia squinado, and of the giant axon of the squid Loligo forbesi. One of the main purposes of these studies has been to find out whether the pH difference between the inside of the fibres and their surroundings varies in the manner predicted by the Donnan equilibrium theory (Donnan, 1911), according to which the following relationship should hold (at 20°C) for a membrane permeable to H+ ions:Internal pH -pH of surroundings =log10 (H+ activity in surroundings) (Internal H+ activity) Resting potential (in mV) 58*17 (Note that this formulation differs from that given in the previous paper in that the resting potential is regarded here as being a negative quantity under normal conditions.)A preliminary account of some of the work described in this paper was given to the 3rd International Congress of Biochemistry (Caldwell, 1955). METHODSGeneral. In many respects the methods were the same as those described previously (Caldwell, 1954). Most of the experiments were carried out with the form of the micro-glass electrode to which was attached a 20-30It capillary electrode. This capillary electrode was filled with crab * Beit Memorial Fellow.t Present address.

In the previous paper (Caldwell, 1960) it was shown that the phosphagen and adenosine triphosphate (ATP) of squid giant axons break down in the presence of fairly high concentrations of inhibitors such as cyanide, dinitrophenol or azide and that some recovery occurs when the inhibitors are removed. Since these agents also reduce the outflow of sodium ions from giant axons to a low value (Hodgkin & Keynes, 1955) it is natural to suppose that ATP or some other energy-rich phosphate compound may provide the energy for running the ionic transport system. This would fit with the generally accepted view as to the function of ATP in linking biochemical and physiological events in cells (Lipmann, 1941). The aim of the experiments described here was to test the assumption by seeing whether injected ATP or arginine phosphate could restore normal ion transport to a fibre poisoned with cyanide or dinitrophenol. The results show that both arginine phosphate and ATP have a restorative action, but that the former is a more effective substitute for normal metabolic activity.

No abstract

The work described in this paper was undertaken as a result of the finding of Hodgkin & Keynes (1955) that the sodium efflux from the giant axons of cephalopods can be markedly reduced by the action of metabolic inhibitors. Hodgkin and Keynes showed that the efflux of 24Na from the giant axons of the squid Loligo forbesi and the cuttlefish Sepia officinalis was reduced when the axons were immersed in artificial sea water containing cyanide, 2. 4-dinitrophenol (DNP) or azide. If at a later stage the axons were immersed in inhibitor-free artificial sea water there was a substantial recovery of the efflux. In experiments with Sepia axons the changes in the 24Na efflux were found to correspond with changes in the 42K influx, which decreased in the presence of the inhibitors and increased again when the inhibitors were removed. The 24Na influx and the 42K efflux were not, on the other hand, affected to a significant extent by the inhibitors. The effects of metabolic inhibitors on the sodium efflux from the giant axons of the squid Loligo pealii have been studied by Shanes & Berman (1955) and it was shown that anoxia causes a decrease in the efflux of 22Na. Shanes and Berman also treated some axons with monoiodoacetate and their results suggest that this inhibitor does not affect the sodium efflux. The effects of ouabain on the 22Na efflux from the giant axons of Loligo forbesi have been studied (Caldwell & Keynes, 1959) and this substance has been found to cause a sharp fall in the efflux.Various suggestions have been made about the way in which the energy required for the active transport of ions across cell membranes may be derived from metabolism. The most notable of these are the Redox Pump theory of Conway (see, for example, Conway, 1958) and the idea that the transport of ions may be linked in some way to the phosphate esters in the cell, in particular to those with 'high-energy' phosphate bonds. Since metabolic inhibitors had been found to inhibit the efflux of sodium and the influx of potassium of cephalopod axons it seemed that an investigation of their effects on the phosphorus metabolism might provide evidence for a * Johnston, Lawrence and Moseley Research Fellow.