Reversibility of thermal injury to myocardial protein synthesis

The ability of transient temperature variations for up to 120-min duration to affect myocardial protein synthesis (MPS) with return to normal temperatures was evaluated using 14C-phenylalanine incorporation into total protein of isolated rabbit right ventricular papillary muscles as in vitro model. Muscles were incubated in oxygenated Krebs-Ringer bicarbonate buffer containing tracer amino acid at temperatures of 28-43 degrees C or incubated without tracer at the same temperatures for up to 120 min and then incubated at 37 degrees C for an additional 2 hr with the tracer amino acid present for the final hour of incubation. Higher as well as lower than physiological temperatures depressed MPS. Recovery from thermal injury to MPS was significantly incomplete when the experimental temperature deviated by 6 degrees C or more from the control (28 and 43 degrees C, respectively) and exposure exceeded 60-min duration. Specific activity of the intracellular amino acid pool was directly measured, and variations in specific activity of the tracer pool were not responsible for the observed effects on MPS. Methylprednisolone (10(-5)M), chloroquine phosphate (10(-5) M), and glucose (15 mM) if present during hyperthermia did not ameliorate thermal damage. It is concluded that hypothermia causes inhibition as well as a degree of irreversible inactivation of the protein synthetic mechanism whereas hyperthermia causes predominant denaturation and irreversibile damage to MPS.