Alterations in surface activity of pulmonary surfactant in Gould's wattled bat during rapid arousal from torpor

The small microchiropteran bat, Chalinolobus gouldii, undergoes large daily fluctuations in metabolic rate, body temperature, and breathing pattern. These alterations are accompanied by changes in surfactant composition, predominantly an increase in cholesterol relative to phospholipid during torpor. Furthermore, the surface activity changes, such that the surfactant functions most effectively at that temperature which matches the animal's activity state. Here, we examine the surface activity of surfactant from bats during arousal from torpor. Bats were housed at 24 degreesC on an 8:16 h light:dark cycle and their surfactant was collected during arousal (28 < T-b < 32 degreesC). Surface activity was examined with a Captive Bubble Surfactometer at 24 and 37 degreesC. Surfactant from arousing bats was more active at 37 degreesC than at 24 degreesC, indicated by a lower STmin and reduced film area compression required to reach STmin. It appears that the arousal-induced changes in surfactant composition, i.e., lower levels of cholesterol, inhibit adsorption of surfactant at 24 degreesC. Furthermore, the alterations in surfactant composition during arousal are very rapid, such that the mixture behaves more like surfactant from warm-active bats, and therefore, functions more effectively at 37 degreesC. (C) 2003 Elsevier Inc. All rights reserved.