Glycerol kinase activity and glycerol metabolism of rat granular pneumocytes in primary culture

Abstract

Glycerol kinase activity and glycerol utilization by rat granular pneumocytes were determined in order to investigate the rate-limiting step for glycerol incorporation into lung lipids. Granular pneumocytes were isolated in primary culture following trypsinization of rat lungs. Glycerol kinase activity was 8.2 nmol/h per 10 6 cells. Incorporation of [1,3- 14C]glycerol into total cell lipids was 0.29 nmol/h per 10 6 cells. In the presence of saturating glycerol concentrations, production of 3H 2O from [2- 3H]glycerol was 13 times greater than incorporation of [ 14C]glycerol into lipids. Glycerol phosphate dehydrogenase activity in isolated cells was approximately 10 times glycerol kinase activity. In the presence of 5.6 mM glucose, glycerol incorporation into lipids was decreased 79% and detritiation of glycerol was decreased 34%. This effect of glucose was due to a 25% increase in cell glycerol 3-phosphate content, resulting in dilution of the precursor pool and possible inhibition of glycerol phosphorylation. These results indicate that the relatively limited incorporation of glycerol into surfactant phospholipids by lung epithelial cells reflects the relatively high rate of glycerol 3-phosphate oxidation.