Metabolism of rat granular pneumocytes isolated in primary culture

Granular pneumocytes (GP) were isolated by trysinization of minced rat lungs followed by short-term primary culture. The yield from the lungs of one rat was approximately 3.5 X 10(6) GP representing 25 micrograms DNA and 0.5 mg protein. Depending on the method to remove cells from attachment to plastic, the purity was 82--92% GP of which > 90% excluded erythrosin B. Resting O2 consumption (37 degrees C) of cells was 202 +/- 29 (mean +/- SE, n = 3) nmol.h-1.(10(6) cells)-1 with a 2.5 times increase in the presence of an uncoupler of oxidative phosphorylation. ATP content of resting pneumocytes was 4.1 +/- 0.18 nmol.(10(6) cells)-1 and was markedly depressed by the "uncoupling" agent. During incubation with [U-14C]glucose, production of metabolites in nmol.h-1.(10(6) cells)-1 was lactate 58.0 +/- 7.9, pyruvate 25.8 +/- 3.2, and 14CO2 56.4 +/- 2.1, and glucose utilization was 104 +/- 38.5. Sonicated GP had higher activities of both lactate and succinate dehydrogenases compared with alveolar macrophages. Alkaline phosphatase activity was localized predominantly to GP, whereas macrophages contained predominantly acid phosphatase. The intracellular water space for granular pneumocytes was 0.55 +/- 0.05 ml.(10(6) cells)-1 and was 71% greater for alveolar macrophage. The presence of active glycolytic and oxidative pathways and appropriate responses to metabolic inhibitors and substrates suggest the presence of intact cell membranes and the retention of metabolic control mechanisms in this isolated lung epithelial cell preparation.