Cibacron blue stimulation of surfactant secretion in rat type II pneumocytes

1 The effect of cibacron blue, a selective P 2y ‐purinoceptor antagonist in some systems, on the stimulatory effect of adenosine 5′‐triphosphate (ATP) on [ 3 H]‐phosphatidylchloine secretion was examined in primary cultures of rat type II pneumocytes prelabelled by overnight culture with [ 3 H]‐choline. 2 Cibacron blue alone stimulated phosphatidylcholine secretion in a concentration‐dependent manner in the range 10 −4 −10 −3 m . At a concentration of 10 −4 or lower, cibacron blue had no effect on ATP‐induced phosphatidylcholine secretion but at 10 −4 −10 −3 m it increased the effect of ATP. Enhancement of the ATP effect was apparent whether cibacron blue was added before or together with ATP. Cibacron blue also increased ATP‐induced secretion in the presence of the P 1 ‐purinoceptor antagonist, xanthine amine congener (10 −5 m ). 3 The stimulatory effect of cibacron blue on phosphatidylcholine secretion was additive to those of 5′ (N‐ethylcarboxyamido) adenosine (NECA) and terbutaline but less than additive to that of ATP. 4 Cibacron blue alone had no effect on formation of cyclic AMP or inositol phosphate and when added stimultaneously with ATP it did not affect the ATP‐induced increase in these second messengers. Preincubation of the cells with cibacron blue before addition of ATP, however, resulted in antagonism of the ATP‐induced increase in cyclic AMP and inositol phosphates. Preincubation with ATP had the same effect. The stimulatory effects of NECA and terbutaline on cyclic AMP formation were enhanced by preincubation with cibacron blue. 5 Thus, ATP‐induced phosphatidylcholine secretion in type II cells is not diminished by the P 2y ‐antagonist, cibacron blue. On the contrary, cibacron blue stimulates phosphatidylcholine secretion. Cibacron blue may act as a P 2 ‐agonist in type II pneumocytes.