Neurochemical and thermal control of surfactant secretion by alveolar typeII cells isolated from the marsupial, Sminthopsis crassicaudata

Pulmonary surfactant is synthesised in alveolar type II cells and secreted into the lining of the lung in response to ventilation, temperature changes and autonomic neurotransmitters. Type II cells were isolated from the hete rothermic marsupial, Sminthopsis crassicaudata. The neurotransmitters, isop roterenol and carbamylcholine chloride significantly increased phosphatidyl choline secretion at 37 degreesC (basal: 14.2%, isoproterenol: 20.1%, carba mylcholine: 17.0%). Temperature reduced the rate of secretion from dunnart type II cells (e.g. basal: 14.2% at 37 degreesC; 7.2% at 18 degreesC). Howe ver, the change in secretory rate between 37 degreesC and 18 degreesC was l ess than expected if due to temperature alone (Q(10)=1.4). The surfactant s ecretory pathway is therefore modulated by factors other than and in additi on to, temperature. The response of dunnart type II cells to the agonists r emained the same at both temperatures. Basal secretion was higher in dunnar t type II cells (14.2% in 4 h) than has been reported in rat type II cells (1.9% in 3 h) and consequently, the agonist-stimulated increases in secreti on from dunnart type II cells (41% above basal in 4 h) were much lower than observed for rat type II cells (200% above basal in 1.5 h).