Release of Proteins from Isolated Neonatal Rat Cardiomyocytes Subjected to Simulated Ischemia or Metabolic Inhibition is Independent of Molecular Mass

This study addressed the question whether the molecular mass of proteins influences their release from isolated rat neonatal cardiomyocytes subjected to simulated ischemia (SI) or metabolic inhibition (MI). During these interventions cellular ATP content and the relative releases of several proteins, ranging in molecular mass from 15 to 140 kDa, were determined. After 180 min of normoxia, cellular ATP content was about 90% of the initial value, and cellular protein loss was about 1%. During either SI (180 min) or MI (120 min) the cellular ATP content decreased to less than 5% of the initial value. After 180 min of SI the release of soluble cytoplasmic proteins from the cells had increased to about 35%, and after 120 min of MI to about 90%. There were no major differences in the release pattern of four cytoplasmic proteins, during both SI and MI. A soluble mitochondrial and a partly mitochondrial protein, however, showed delayed release patterns. These data indicate that the release of proteins from damaged isolated neonatal rat cardiomyocytes is not related to the molecular mass of the proteins. It is concluded that protein release from damaged cardiomyocytes is not a sieving process in which small proteins are preferentially lost. In contrast, our data suggest that sarcolemmal disruption is a relatively fast process resulting in the simultaneous release of all soluble cytoplasmic proteins, irrespective of their molecular mass.