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First published online July 23, 2003

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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

View larger version (147K): [in a new window]   Fig. 1. Electron micrograph of an alveolar type II epithelial cell in lung tissue isolated from the golden mantled-ground squirrel Spermophilus lateralis. Scale bar, 2 µm. AS, air space showing surfactant myelin material; LB, lamellar body; N, nucleus.

View larger version (33K): [in a new window]   Fig. 2. Regulation of surfactant phosphatidylcholine (PC) secretion by the adrenergic agonist, isoproterenol (100 µmol l-1) and the cholinergic agonist, carbamylcholine chloride (Carbachol, 100 µmol l-1), in alveolar type II cells isolated from warm-active and torpid ground squirrels. Both warm-active and torpid cells were assayed at 37°C and 4°C for 0.5 and 1 h. *Significant increase above basal secretion for each experimental group (paired t-test, P<0.05). Significant difference in secretion between matching experimental groups measured at the two different assay temperatures, i.e. 0.5 h/torpid/4°C vs 0.5 h/torpid/37°C (t-test, P<0.05). Significant difference in % secretion between warm-active cells assayed at 37°C and torpid cells assayed at 4°C (t-test, P<0.05). Bars represent % of incorporated [3H]choline secreted as phosphatidylcholine (mean ± S.E.M.) for N experiments after 0.5 and 1 h; for warm-active animals, N=4; for torpid animals, N=5. % secretion = % c.p.m. measured in the medium divided by the total cpm (cells + medium)x100 measured for each sample.

View larger version (33K): [in a new window]   Fig. 3. The production of cAMP (pmoles 10-6 cells) in alveolar type II cells isolated from warm-active and torpid ground squirrels and assayed at two assay temperatures (37°C and 4°C). cAMP production was calculated using a direct cAMP ELISA kit (Amersham Pharmacia, Sydney, Australia). Bars represent the amount of cAMP produced (mean ± S.E.M.) in N=5 experiments in all cases. *Significant increase above basal cAMP production for each experimental group; significant difference between warm-active cells assayed at 37°C and torpid cells assayed at 4°C (t-test, P<0.05).