Influence of the protein kinase C inhibitor 3-[1-[3-(amidinothio) propyl]-1H-indoyl-3-yl]-3-(1-methyl-1H-indoyl-3-yl) maleimide methane sulfonate (Ro-318220) on surfactant secretion in type II pneumocytes.

We have investigated the influence of 3-[1-[3-(amidinothio)propyl]-1H-indoyl-3-yl]-3-(1-methyl-1H- indoyl-3-yl) maleimide methane sulfonate (Ro-318220), a potent and selective inhibitor of protein kinase C, on phosphatidylcholine secretion in response to surfactant secretagogues in rat type II cells. Freshly isolated cells were cultured overnight with [3H]choline to label the phosphatidylcholine pool and were preincubated for 30 min in fresh medium with or without Ro-318220. Secretagogues were then added, and the incubation was continued for 90 min after which [3H]phosphatidylcholine secretion was measured. Ro-318220 (10 microM) almost completely abolished the stimulatory effects of 36 microM terbutaline, 10 microM ATP, and 1 microM 12-O-tetradecanoylphorbol-13-acetate (TPA) and significantly antagonized the effects of 10 microM 5'-(N-ethylcarboxyamido) adenosine (NECA), 100 microM dioctanoylglycerol, and 0.05 microM ionomycin. The effect of Ro-318220 was dependent on concentration. The IC50 values for Ro-318220 inhibition of the effects of terbutaline, NECA, TPA, and ionomycin were not significantly different. The IC50 value for Ro-318220 inhibition of the effect of TPA in the type II cell (0.05 microM) was similar to that reported for inhibition of protein kinase C in vitro (0.08 microM). We conclude that Ro-318220 antagonizes the effects of the different surfactant secretagogues by antagonizing a step common to the different signaling pathways. It remains to be established if it is protein kinase C or another step that is inhibited.