Mechamism on amylase secretion

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Roles of cGMP on salivary secretion were investigated using atrial natriuretic peptide (ANP) which is known as activator of quanylate cyclase.1) The amount of ^<125>I-ANP specific binding to plasma membrane of rat parotid and submandibular gland increased in proportion to the amount of protein used and reached to plateau. ANP competed binding of ^<125>I-ANP with the membrane protein, and IC_<50> values for parotid and submandibular gland membrane were 5 X 10^<19>M and 10^<19>M, respectively. The results indicated the presence of ANP receptor protein in the salivary glands.2) Rat parotid acinar cells were incubated with ANP or carbachol.Caubachol (10^<-5>M) had no detectable effect on cGMP accumulation (only 5%). However, ANP(10^<-7>M) enhanced cGMP levels with an approximately 2-fold increase. ANP alone didn't cahange cAMP accumulation, but inhibited cAMP accumulation stimulated by forskolin.ANP, nitroprusside (NP) and hydroxylamine (HA) enhanced cGMP in the presence or absence of forskolin. ANP inhibited cAMP accumulation stimulated by forskolin, but NP and HA did not affect. Further more, ANP inhibited amylase resease from rat parotid acinar cells stimulated by forskolin, di-Bu-cAMP and isoproterenol, but NP and HA didn't inhibite. The results indicated cGMP does not mediate cAMP accumulation and amylase secretion directly.4) The inhibition of amylase release and cAMP accumulation by ANP was inhibited by treatment of parotid gland or plasma membrane of parotid gland with pertussis toxin (PT). Treatment of membrane with PT afforded ribosylated protein. The results suggested that the inhibition of adenylate cyclase by ANP may be mediated by Gi protein through ANP clearance receptor.5) To investigate the effect of cGMP on cGMP-stimulated phosphodiesterase (PED), identifications of PDEs were performed using specific PDE-inhibitors and estimation of molecular weight of PDEs in rat parotd gland. Type I, II, III and IV cAMP-specific-PDEs were identified.