PROTEIN-SYNTHESIS IN THE HEART IN-VIVO, ITS MEASUREMENT AND PATHO-PHYSIOLOGICAL ALTERATIONS

Changes in cardiac protein composition occur in a variety of patho-phy siological situations and are usually accompanied by modifications in protein synthesis. Although adjustments in protein synthesis during st arvation may be adaptive, the alterations in protein synthesis seen in response to ethanol ingestion may be pathological and an important st ep in the genesis of alcoholic heart muscle disease. The alterations i n heart muscle in hypertension are initially adaptive but in the long term they are deleterious, and involve both transcription and translat ion. While adequate methods exist for quantifying the amount of mRNA f or contractile and non-contractile proteins, such studies of gene-expr ession provide no dynamic information on the rate at which tissue prot eins are lost or accrued. This can only be determined by measuring the rate of protein turnover, i.e, either protein synthesis or protein br eakdown. Techniques for directly determining the rates of protein brea kdown are limited or involve surgical procedures. Methods for measurin g the rate of protein synthesis are described, and are illustrated by their application to the investigation of starvation and ethanol toxic ity, In particular, attention is focused on the fact that reliable rat es of protein synthesis are obtained only if the specific radioactivit y of the precursor at the site of protein synthesis (aminoacyl-tRNA) i s assessed.