Involvement of calcium in the stimulation of phosphatidylcholine secretion in primary cultures of rat type II pneumocytes by Escherichia coli lipopolysaccharide

The purpose of this study was to evaluate the mechanism by which Escherichia coli lipopolysaccharide stimulates the secretion of phosphatidylcholine in primary cultures of rat type II pneumocytes. The stimulatory effect of lipopolysaccharide on phosphatidylcholine secretion was additive to those of terbutaline and TPA (protein kinase A and C activators respectively) and this effect was not suppressed by inhibitors of both protein kinases. On the other hand, lipopolysaccharide did not modify the increase on phosphatidylcholine secretion induced by the endoplasmic reticulum Ca²⁺-ATPase inhibitor thapsigargin, and enhanced slightly the calcium-ionophore A23187 stimulated phosphatidylcholine secretion. In addition, the stimulatory effect of lipopolysaccharide was suppressed by BAPTA, an intracellular Ca²⁺ chelator, and KN-62, a specific inhibitor of Ca²⁺-calmodulin-dependent protein kinase. These results, together with the lipopolysaccharide-mediated increase in the cytosolic [Ca²⁺], suggest that stimulation of phosphatidylcholine secretion by lipopolysaccharide in type II pneumocytes occurs by a calcium-dependent transduction mechanism via Ca²⁺-calmodulin-dependent protein kinase activation.