CHOLERA-TOXIN ENHANCED CAMP PRODUCTION STIMULATED BY PACAP IN HUMAN NEUROBLASTOMA NB-OK-1 CELLS

The purpose of these experiments was to examine the effect of PACAP an tagonists on cAMP production stimulated by PACAP-38, PACAP-27, and the related peptides and the effect of cholera toxin on cAMP production s timulated by PACAPs and the related peptides, on human neuroblastoma N B-OK-1 cell. The C-terminal fragments of PACAPs such as PACAP (5-38), PACAP (10-38) and PACAP (8-27) at 10(-6)M reduced significantly cAMP p roduction stimulated by PACAP-38 or PACAP-27 at 10(-8)M with 83%, 80% and 70% inhibition, respectively, while the N-terminal fragment such a s PACAP (1-15) did not show ally antagonistic activity. In contrast, T he cAMP production stimulated by VIP or helodermin at 10(-8)M, was par tially inhibited but very weakly by these C-terminal fragments at 10(- 6)M. Furthermore, effects of PACAP-38, PACAP-27 and VIP on cAMP produc tion in cholera toxin-pretreated human neuroblastoma cells NB-OK-1 wer e examined. Addition of PACAP-38 or PACAP-27 at 10(-8)M to the neurobl astoma cells NB-OK-1 pretreated with cholera toxin (100ng/ml) for 3 hr resulted in a marked increase of cAMP production within 30 min, while VIP or helodermin at 10(-8)M did not cause any significant effect on cAMP production in the cholera toxin-treated cells. PACAP-38 and PACAP -27 at 10(-6)M remained unaffected to occupy the receptors in the chol era toxin-treated cells, while preincubation of the cells with cholera toxin resulted in 50-60% reduced binding activity of VIP at 10(-6)M.