ALTERATIONS IN THE SURFACE-PROPERTIES OF LUNG SURFACTANT IN THE TORPID MARSUPIAL SMINTHOPSIS-CRASSICAUDATA

Torpor changes the composition of pulmonary surfactant (PS) in the dun nart Sminthopsis crassicaudata [C. Langman, S. Orgeig, and C. B. Danie ls. Am. J. Physiol. 271 (Regulatory Integrative Comp. Physiol. 40): R4 37-R445, 1996]. Here we investigated the surface activity of PS in vit ro. Five micrograms of phospholipid per centimeter squared surface are a of whole lavage (from mice or from warm-active, 4-, or 8-h torpid du nnarts) were applied dropwise onto the subphase of a Wilhelmy-Langmuir balance at 20 degrees C and stabilized for 20 min. After 4 h of torpo r, the adsorption rate increased, and equilibrium surface tension (STe q), minimal surface tension (STmin), and the %area compression require d to achieve STmin decreased, compared with the warm-active group. Aft er 8 h of torpor, STmin decreased [from 5.2 +/- 0.3 to 4.1 +/- 0.3 (SE ) mN/m]; %area compression required to achieve STmin decreased (from 4 3.4 +/- 1.0 to 27.4 +/- 0.8); the rate of adsorption decreased; and ST eq increased (from 26.3 +/- 0.5 to 38.6 +/- 1.3 mN/m). ST-area isother ms of warm-active dunnarts and mice at 20 degrees C had a shoulder on compression and a plateau on expansion. These disappeared on the isoth erms of torpid dunnarts. Samples of whole lavage (from warm-active and 8-h torpor groups) containing 100 mu g phospholipid/ml were studied b y using a captive-bubble surfactometer at 37 degrees C. After 8 h of t orpor, STmin increased (from 6.4 +/- 0.3 to 9.1 +/- 0.3 mN/m) and %are a compression decreased in the 2nd (from 88.6 +/- 1.7 to 82.1 +/- 2.0) and 3rd (from 89.1 +/- 0.8 to 84.9 +/- 1.8) compression-expansion cyc les, compared with warm-active dunnarts. ST-area isotherms of warm-act ive dunnarts at 37 degrees C did not have a shoulder on compression. T his shoulder appeared on the isotherms of torpid dunnarts. In conclusi on, there is a strong correlation between in vitro changes in surface activity and in vivo changes in lipid composition of PS during torpor, although static lung compliance remained unchanged (see Langman et al . cited above). Surfactant from torpid animals is more active at 20 de grees C and less active at 37 degrees C than that of warm-active anima ls, which may represent a respiratory adaptation to low body temperatu res of torpid dunnarts.