SUMMARY1. A study has been made of the relationship between the concentration of internal calcium and the permeability of human red cell membranes to sodium and potassium.2. Fresh red cells contain very little calcium, but after being depleted of ATP by ageing they took up calcium from Ringer solution. The entry was unaffected by external sodium and potassium but was markedly pH dependent. When supplied with energy, calcium-loaded cells actively extruded calcium by a saturable process which was also unaffected by the distribution of sodium and potassium across the membranes. The activity of the calcium pump was sufficient to maintain the low internal concentration found under physiological conditions.3. Raising internal calcium in metabolically poor cells caused a loss of cell potassium which was greater than the concomitant sodium gain. These changes were reversed when ATP was supplied. External calcium had no effect. The increase in permeability to sodium and potassium was enhanced by the simultaneous addition of fluoride, and, even more so, of iodoacetate. These inhibitors had no effect on membrane permeability unless calcium was also present. Inosine potentiated the action of fluoride and iodoacetate in causing potassium loss, by allowing more calcium to enter the cells.4. The results suggest that the permeability of human red cell membranes to sodium and potassium is regulated by internal calcium, which in turn is controlled by a calcium pump that utilizes ATP.

It is generally recognized that the oxygen consumption of cells is related to the amount of free energy being utilized by such processes as secretion, contraction, and the synthesis of complex molecules. Two questions arise concerning the nature of the coupling between energy release from metabolism and its utilization. First, what fraction of the cell's total metabolism is devoted to a particular energy-requiring process; and secondly, how is an increase in oxygen consumption elicited in order to ensure a supply of the requisite energy? This paper deals with these problems in connexion with the active movements of ions in kidney cortex slices.In slices of kidney cortex from adult rabbits and guinea-pigs the establishment and maintenance of concentration gradients of sodium and potassium ions between intracellular and extracellular fluid depends on energy from respiration (Mudge, 1951 a, b;Whittam & Davies, 1953). The evidence for this is chiefly the fact that active transport is stopped when the energy supply is decreased by the inhibition of respiration. Such studies have not revealed the fraction of the total respiratory energy expended on these ion movements or whether the latter in turn influence the rate of respiration. Kidney cortex is a particularly suitable tissue for studying the interdependence of ion transport and metabolism, because both its rate of respiration and the turnover rate of its potassium are high, so that a reduction in oxygen uptake which might result from stopping transport could easily be measured. The coupling between respiration and potassium transport in slices of kidney cortex has been investigated in the present study by comparing the effects of ouabain, sodium ion, oc-oxoglutarate, and temperature on tissue potassium concentration and respiration during incubation at 25 and 380 C. A preliminary account of this work has been reported previously (Whittam & Willis, 1962).

1. A study has been made of the dependence on the concentrations of internal Na(+) and external K(+) of lactate and phosphate production in human erythrocytes. 2. Lactate production was stimulated by Na(+) and K(+) but only when they were internal and external respectively. The stimulation was counteracted by ouabain. The production of phosphate was affected in the same way. 3. There is a quantitative correlation between these effects and those previously found for cation movements and the membrane adenosine triphosphatase. 4. It is concluded that the rate of energy production in glycolysis is partly controlled by the magnitude of active transport; the extent of this regulation is shown to vary from 25 to 75% of a basal rate that is independent of active transport. 5. The activity of the membrane adenosine triphosphatase was also compared with rates of Na(+) and K(+) transport. The latter were varied by altering the concentrations of internal Na(+) and external K(+), and by inhibiting with ouabain. 6. A threefold variation of active transport rate was accompanied by a parallel change in the membrane adenosine-triphosphatase activity. The results show a constant stoicheiometry for the number of ions moved/mol. of ATP hydrolysed, independent of the electrochemical gradient against which the ions were moved. 7. Calculations show that the amount of ATP hydrolysed would provide enough energy for the osmotic work. The results are discussed in relation to possible mechanisms for active transport.

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