Intracellular disruption of rat heart lysosomes by leucine methyl ester: effects on protein degradation.

Perfusion of rat hearts with Krebs--Henseleit medium containing 10 mM L-leucine methyl ester leads to swelling of lysosomes and loss of lysosomal integrity within 30-60 min. No morphological changes can be detected in the nuclei, mitochondria, sarcoplasmic reticulum, or Golgi complex as a result of the treatment with leucine methyl ester, and the hearts continue to beat normally during the treatment period. Homogenates of rat hearts perfused with the methyl ester exhibit a decrease in the sedimentability of cathepsin D activity compared to controls, thus providing additional evidence for a loss of lysosomal integrity. Swelling and disruption of the lysosomes presumably occurs because of the extensive accumulation of leucine within the organelles resulting from the intralysosomal hydrolysis of the freely permeating methyl ester. The lysosomal dysfunction that occurs with exposure to leucine methyl ester produces a 30% decrease in cardiac protein degradation. These results provide an estimate of the contribution of lysosomes to total protein degradation in the rat heart, and they also suggest that the enzymes released as a result of lysosomal disruption are relatively inactive in hydrolyzing cellular constituents under the perfusion conditions used here. The use of amino acid methyl esters to produce rapid, specific loss of lysosomal integrity in situ provides an approach to the study of lysosomal function in intact cells.