Torpor-associated fluctuations in surfactant activity in Gould's wattled bat

The primary function of pulmonary surfactant is to reduce the surface tension (ST) created at the air-liquid interface in the lung. Surfactant is a complex mixture of lipids and proteins and its function is influenced by physiological parameters such as metabolic rate, body temperature and breathing. In the microchiropteran bat Chalinolobus gouldii these parameters fluctuate throughout a 24 h period. Here we examine the surface activity of surfactant from warm-active and torpid bats at both 24degreesC and 37degreesC to establish whether alterations in surfactant composition correlate with changes in surface activity. Bats were housed in a specially constructed bat room at Adelaide University, at 24degreesC and on a 8: 16 h light:dark cycle. Surfactant was collected from bats sampled during torpor (25 < T-b < 28degreesC), and while active (T-b > 35degreesC). Alterations in the lipid composition of surfactant occur with changes in the activity cycle. Most notable is an increase in surfactant cholesterol (Chol) with decreases in body temperature [Codd et al., Physiol. Biochem. Zool. 73 (2000) 605-612]. Surfactant from active bats was more surface active at higher temperatures. indicated by lower STmin and less film area compression required to reach STmin at 37degreesC than at 24degreesC. Conversely, surfactant from torpid bats was more active at lower temperatures. indicated by lower STmin and less area compression required to reach STmin at 24degreesC than at 37degreesC, Alterations in the Chol content of bat surfactant appear to be crucial to allow it to achieve low STs during torpor. (C) 2002 Elsevier Science B.V. All rights reserved.