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First published online July 23, 2003

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The Journal of Experimental Biology 206, 3031-3041 (2003)
doi: 10.1242/jeb.00519

Thermal acclimation of surfactant secretion and its regulation by adrenergic and cholinergic agonists in type II cells isolated from warm-active and torpid golden-mantled ground squirrels, Spermophilus lateralis

Carol J. Ormond¹, Sandra Orgeig^1,*, Christopher B. Daniels¹ and William K. Milsom²

¹ Environmental Biology, School of Earth and Environmental Sciences, University of Adelaide, Adelaide SA 5005, Australia
² Department of Zoology, University of British Columbia, Vancouver BC V6T1Z4, Canada

^* Author for correspondence (e-mail: sandra.orgeig{at}adelaide.edu.au)

Accepted 28 May 2003

Homeothermic mammals experience pulmonary surfactant dysfunction with relatively small fluctuations in body temperature. However, ground squirrels survive dramatic changes in body temperature during hibernation, when body temperature drops from 37°C to 0-5°C during prolonged torpor bouts. Using type II cells isolated from both warm-active and torpid squirrels, we determined the effect of assay temperature, autonomic agonists and torpor on surfactant secretion. Basal secretion was significantly higher in type II cells isolated from torpid squirrels compared with warm-active squirrels when assayed at the body temperature of the animal from which they were isolated (4°C and 37°C, respectively). A change in assay temperature significantly decreased surfactant secretion. However, the change in secretory rate between 37°C and 4°C was less than expected if due to temperature alone (Q₁₀ range=0.8-1.2). Therefore, the surfactant secretory pathway in squirrel type II cells demonstrates some temperature insensitivity. When incubated at the body temperature of the animal from which the cells were isolated, the adrenergic agonist, isoproterenol, significantly increased surfactant secretion in both warm-active and torpid squirrel type II cells. However, the cholinergic agonist, carbamylcholine chloride, only increased secretion in torpid squirrel type II cells when incubated at 4°C. Torpor did not affect basal cAMP production from isolated type II cells. However, the production of cAMP appears to be upregulated in response to isoproterenol in torpid squirrel type II cells. Thus, at the cellular level, both the secretory and regulatory pathways involved in surfactant secretion are thermally insensitive. Upregulating basal secretion and increasing the sensitivity of type II cells to cholinergic stimulation may be adaptative characteristics of torpor that enable type II cells to function effectively at 0-5°C.

Key words: ground squirrel, Spermophilus lateralis, pulmonary surfactant, hibernation, torpor, alveolar type II cell, cholinergic, adrenergic

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