Stimulation of active transport of sodium from sodium-rich frog muscle by insulin and lactate

Histidine metabolism in experimental protein malnutrition in rats

1. The activities of the enzymes histidase, urocanase and histidine-pyruvate transaminase were studied in rats under conditions of protein malnutrition. Urocanase and histidase activities in liver were markedly lowered in experimental protein malnutrition, but the activity of histidine-pyruvate transaminase was unaffected. There is a metabolic control in vivo of the enzymes involved in the catabolism of histidine. 2. Significant changes in the urinary excretion of histidine, composition of liver and serum were apparent in the protein-malnourished rat. 3. The changes in the activities of the enzymes and other parameters were of a reversible nature and dependent on the nature of the dietary protein. 4. The significance of these findings is discussed in relation to abnormal histidine metabolism in kwashiorkor.

Membrane bound and cellular cationic changes associated with insulin stimulation of cultured cells

Insulin was employed as a stimulant in our continuing investigations of the molecular mechanisms involved in the coordinate control of cellular metabolism and growth. Incubation of chicken embryo fibroblasts for 16 hours in media containing 0-0.1 U insulin/ml resulted in a 17-fold increase in the rate of 3H-thymidine incorporation into DNA. Concomitantly, there were graded increases in intracellular K+ (14%) AND Mg2+ (22%) and no significant change in Ca2+. These changes in cation content occurred within 10 to 30 minutes and preceded the changes in 3H-thymidine incorporation. Insulin produced a consistent graded decrease in externally bound Mg2+ and Ca2+ and a concomitant increase in bound Na+ and K+ with no significant change in the rates of K+ and Mg2+ efflux. The results are consistent with the concept of Mg2+ as a second messenger for insulin action, as well as with the more general hypothesis that Mg2+ is the centtral agent in the coordinate control of metabolism and growth in animal cells.

Energy barriers to sodium extrusion from sodium-rich kidney cortex slices

1. Rat and guinea-pig kidney cortex slices were made Na-rich by leaching in cold NaCl and then allowed to recover in Ringer solution at 30 or 25 degrees C. Net Na extrusion was systematically decreased by the use of re-immersion media with constant Na and diminishing K, or with constant K and increasing Na, and the energy requirements for Na extrusion under these conditions were calculated.2. The critical energy barrier at which no net Na loss can be achieved was somewhat lower in these tissues than found by other authors for frog sartorius muscle.3. Inclusion of pyruvate or insulin and lactate in the recovery fluid had no effect.4. Methylsulphate apparently enters renal cells during incubation and is therefore unsuitable for use with this tissue as a source of impermeant anion.