Pentose pathway of glucose metabolism in isolated granular pneumocytes. Metabolic regulation and stimulation by paraquat.

Activity of the pentose phosphate pathway of glucose metabolism was measured in isolated granular pneumocytes under a variety of metabolic conditions known to alter this pathway in intact lungs. Granular pneumocytes were isolated by trypsinization of rat lungs and maintained in primary culture for 24 hr before use. Cells were incubated for 1 hr at 37 degrees with 5.5 mM glucose specifically labeled as 1-14C, 6-14C, U-14C, or 5-3H for determination of glucose utilization, pentose cycle activity, and partition of CO2 production between mitochondrial and pentose pathways. With control cells, total glucose utilization was 111 +/- 4.8 nmoles X hr-1 X (10(6) cells)-1 (mean +/- S.E., N = 19), and 2.2% was metabolized by the pentose cycle. Pentose cycle CO2 production was 7.3 nmoles X hr-1 X (10(6) cells)-1 representing 34% of total CO2 production. Dinitrophenol (50 microM) stimulated mitochondrial CO2 production 5-fold but had no effect on the pentose cycle activity. Phenazine methosulfate (5 microM) had no effect on mitochondrial activity but stimulated pentose cycle activity 15-fold. Antimycin A (0.4 micrograms/ml) markedly inhibited both pathways. After a 30-min preincubation with paraquat (3 mM), the pentose cycle CO2 production increased to 107 nmoles X hr-1 X (10(6) cells)-1 accounting for 39.6% of glucose utilization and 88.4% of CO2 production. Mitochondrial CO2 production was unchanged with paraquat. These studies demonstrate that the pentose cycle in resting granular pneumocytes accounts for a major fraction of the CO2 production from glucose and that activity of this pathway is regulated by the utilization of cytoplasmic reducing equivalents. Paraquat produces marked stimulation of pentose cycle activity in granular pneumocytes, resulting in maximal utilization of cytoplasmic NADPH.