EFFECT OF PT-TREATMENT ON ANP-MEDIATED INHIBITION OF ADENYLATE-CYCLASE AND AMYLASE RELEASE IN RAT PAROTID-GLAND

Effects of pertussis toxin (PT) treatment on atrial natriuretic peptid e (ANP)-mediated inhibition of adenylate cyclase and amylase release w ere investigated in rat parotid gland. Adenylate cyclase activity stim ulated by GTP gamma S in PT-treated membranes was much larger than tha t in normal membranes. ANP dose-dependently inhibited adenylate cyclas e stimulated by GTP gamma S in control rat parotid membranes, however in membranes prepared from PT-injected (in vivo) rat parotid gland, AN P did not inhibit adenylate cyclase. ANP(10(-7)M) inhibited cAMP accum ulation stimulated by forskolin (10(-6)M) in control rat parotid acina r cells by about 34%, however, in PT-treated cells, the inhibitory eff ect of ANP was attenuated completely. In control cells, amylase releas e stimulated by isoproterenol (10(-6)M) and forskolin (10(-6)M) were a lso depressed by ANP (10(-7)M) by 27 and 30%, respectively. The inhibi tory response of ANP on amylase release was completely attenuated by P T-treatment. Gi was detected as a ADP-ribosylated 41-KDa protein by in cubation of parotid membranes with PT and [alpha-P-32]NAD. In rat paro tid gland, these results suggested that ANP mediates adenylate cyclase /cAMP system and consequently reduces amylase release through ANP-C re ceptor coupled to Gi.