INTRALYSOSOMAL PH AND RELEASE OF LYSOSOMAL-ENZYMES IN THE RAT-LIVER AFTER EXHAUSTIVE EXERCISE

The mechanism underlying exhaustive exercise-induced release of lysoso mal enzymes was studied in the rat liver. Exhaustive exercise resulted in the release of beta-glucuronidase and cathepsin D, but not beta-gl ucosidase and acid phosphatase, into the blood and cytosol, suggesting that the release of lysosomal enzymes is not due to disruption of lys osomal membranes. The intralysosomal pH of the liver, which was approx imately 5.5 at the resting level, rose significantly after exhaustive exercise to pH 6.3. In vitro, beta-glucuronidase and cathepsin D were released at an intralysosomal pH exceeding 6.2. In contrast, beta-gluc osidase and acid phosphatase were not released. The elevation of intra lysosomal pH reduced the aggregation of beta-glucuronidase and catheps in D. The rate of ammonia accumulation increased markedly in the lysos ome-enriched subcellular fraction after exercise. There was a positive relationship between the rate of ammonia accumulation and the elevati on of intralysosomal pH in vitro. Lysosomes isolated after exhaustive exercise showed significantly increased osmotic fragility. Our finding s suggest that, during exhaustive exercise, the accumulation of ammoni a in lysosomes leads to the elevation of intralysosomal pH, resulting in the reduced aggregation of certain lysosomal enzymes. Thus, less ag gregated lysosomal enzymes may be released into the cytosol through th e lysosomal membrane, the permeability of which has been increased.