Mechamism on amylase secretion

1)大鼠腮腺和颌下腺质膜上cGMP的特异性结合量随蛋白质用量的增加而增加，并达到平台期。ANP与膜蛋白竞争结合，腮腺和颌下腺膜的IC50分别为5×10~(-1)M和10~(-10)M。2)大鼠腮腺腺泡细胞与心钠素或卡巴胆碱共同孵育后，番茄碱(10^&lt；-5&gt；M)对cGMP积聚无明显影响(仅5%)。然而，ANP(10^&lt；-7&gt；M)提高了cGMP水平，大约增加了2倍。ANP单独作用不影响cAMP积聚，但可抑制Forskolin刺激的cAMP积聚。ANP、硝普钠(NP)和羟胺(HA)在Forsklin存在或不存在时均可增强cGMP。ANP可抑制Forsklin刺激的cAMP积聚，但NP和HA对此无影响。此外，ANP还能抑制Forskolin、二-Bu-cAMP和异丙肾上腺素刺激的大鼠腮腺腺泡细胞的淀粉酶再释放，但NP和HA对此无抑制作用。4)用百日咳毒素(PT)处理腮腺或腮腺质膜，可抑制ANP对淀粉酶释放和cAMP积累的抑制。用PT处理膜，可获得核糖化蛋白。5)为了研究cGMP对cGMP刺激的磷酸二酯酶(PED)的影响，采用特异性PDE抑制剂对PDE进行鉴定，并测定了PDE的相对分子质量。鉴定出I型、II型、III型和IV型cAMP特异性PDE。

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.