Abstract
We studied membrane potentials of the plasma (Ep) and mitochondrial (Em) membranes of isolated type II alveolar epithelial cells under basal conditions and during surfactant secretion. Ep and Em of freshly isolated rabbit type II cells was measured by determining the distribution ratios of the labeled ionic probes triphenylmethylphosphonium (TPMP+) and Rb+, under conditions which eliminate potential-independent accumulation of probes. Under basal conditions Ep was found to be -63±4mV, similar to values obtained in other secretory epithelial cells. Stimulation of secretion by β-adrenergic agonists caused a 20% hyperpolarization of the cells measurable from 5 to 60 minutes after stimulation. The dose response relationship for the potential change was identical to that observed for secretion with a maximum at 10−5 terbutaline. Both secretion and potential changes were completely inhibited by use of the β-blocker propanolol. Through the use of potential selective poisons the change in potential could be attributed to a change in Ep occurring via the activation of an electrogenic membrane bound Na-K ATPase. These results suggest that ionic movements across the plasma membrane play a role in the secretion of surfactant from type II cells.
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