Recycling of surfactant in black and beige mice: pool sizes and kinetics.

Lung disaturated phosphatidylcholine (DSPC) turnover was investigated in normal C57 black and mutant beige mice; the latter have been postulated to have microtubular defects. Turnover experiments were performed on 117 black and 74 beige mice that were assayed for lamellar body-rich fraction (LB) and alveolar lavage fluid (AF) DSPC from 0.5 to 100 h after injection of [3H]glycerol. The data were analyzed by a program that derived the best-fit rate constants for an operator-chosen compartmental model. For black mice, a simple model with bidirectional exchange of DSPC between LB and AF compartments fitted the data almost as well as more complex models. This model yielded a turnover time of 5.9 h, a biological half-life of 16 h, and recycling of AF DSPC into LB of 47%. There was some evidence to suggest that DSPC might be degraded rather than recycled as a unit. For beige mice, the DSPC turnover time was 4.8 h, and its biological half-life was 40 h. The AF DSPC pool was smaller than in black mice, but the LB pool was larger. The bidirectional flux of DSPC between AF and LB was much greater than in black mice, the percent of recycling being 85. These data do not support a microtubular defect in beige mice, but the calculations for beige mice are based on a model of questionable validity.