Extracellular hydrolases of the lung

Area of Science:

• Pulmonary Medicine
• Cell Biology
• Biochemistry

Background:

• The lungs contain extracellular acid hydrolases in the alveolar lining.
• The activity of these hydrolases is selective, with some highly active and others barely detectable.

Purpose of the Study:

• To investigate the origins of extracellular acid hydrolases found in lung lavage fluid.
• To determine if serum leakage or cell damage contributes to their presence.

Main Methods:

• Pulmonary lavage was used to collect acellular lining material.
• Electrophoretic analysis was performed on acrylamide gels.
• Lactate dehydrogenase levels were measured to assess cell damage.
• Lamellar bodies were isolated from lung homogenates.

Main Results:

• Extracellular hydrolase activity was highly selective (e.g., high beta-N-acetylglucosaminidase, low beta-glucuronidase).
• Hydrolase profiles differed from serum enzymes.
• Lactate dehydrogenase measurements confirmed minimal cell damage during lavage.
• Isolated lamellar bodies contained hydrolases similar to those found extracellularly.

Conclusions:

• Extracellular hydrolases in lung lavage do not originate from serum leakage or cell damage.
• These enzymes are likely selected by alveolar type 2 cells during lamellar body formation.
• Lamellar bodies are the probable source of extracellular acid hydrolases in the distal airways.