Patients with renal failure, diabetic ketosis, severe trauma or sepsis often become acidotic. Moreover, they are also susceptible to body protein wasting. Experimental acidosis has been shown to result in negative nitrogen balance, and body protein loss in acidotic patients can be alleviated by normalization of pH. Previous work has concentrated on the effects of pH on protein degradation and no systematic studies have been performed on pH and protein synthesis. However, measurements in animals and human volunteers have shown that both metabolic and respiratory acidosis are associated with depressed rates of synthesis of skeletal muscle protein and serum albumin. The purpose of the present proposal is therefore to characterize the relationship between protein synthesis rates in tissues, especially muscle and liver, of rats and humans in relation to changes in intra- and extracellular pH, to confirm the hypotheses: (i) that changes in blood pH, both by metabolic and respiratory means, modify rates of tissue protein synthesis and gene expression and contribute to the protein wasting of patients with acidosis, and (ii) that these effects of pH operate directly via the intracellular pH and do not involve extracellular mediators such as hormones. The studies will employ measurements of rates of protein synthesis in tissues of rats and human volunteers to characterize the responses to changes in intra- and extracellular pH induced by metabolic and respiratory means and to confirm that these effects are rapid, operate over the full range of pH from acidosis to alkalosis and are independent of oxygen supply. In the animals, the responses of gene expression in the liver will be investigated by determining the levels of mRNA for 3 liver proteins. In particular, the treatments studied will produce different changes in the infra- and extracellular pH. Measurements of intracellular pH will be made by nuclear magnetic resonance, to confirm the hypothesis that changes in protein synthesis are determined by the intracellular rather than extracellular pH. A separate set of studies will be performed in isolated tissues and cells, to determine whether responses to changes in pH are direct or act through circulating hormones. The cellular and molecular mechanisms through peptide chain initiation and initiation factors eIF-2 and eIF-4 will also be identified. Finally, the effect of changes in pH on tissue protein synthesis will be measured in human volunteers and hemodialysis patients, to identify the role of pH control of protein synthesis in health and in protein wasting conditions with abnormalities of pH control.
