Resink T J, Scott-Burden T, Baur U, Jones C R, Bühler F R
Department of Research, University Hospital, Basel, Switzerland.
Eur J Biochem. 1988 Mar 1;172(2):499-505. doi: 10.1111/j.1432-1033.1988.tb13915.x.
Discrepancies exist between extent of guanylate cyclase activation by atrial natriuretic peptide (ANP) in cell-free systems and ANP-stimulated levels of cyclic GMP in whole cells, and also between receptor affinity and dose effectiveness of ANP. Therefore, we have investigated whether, in addition to receptor-coupled guanylate cyclase activation, other second-messenger cascade systems may be involved in mediating both an increase in cyclic GMP and the physiological response to ANP. Equilibrium 125I-ANP binding studies on cultured thoracic aorta smooth muscle cells revealed the existence of low-affinity (approximately 10(-8) M, 84.5 fmol/10(5) cells) and high-affinity (approximately 10(-10) M, 12.5 fmol/10(5) cells) binding sites. We confirm that ANP elevates intracellular cyclic GMP (EC50 approximately 10(-8) M) and inhibits agonist-(isoproterenol and forskolin)-induced increases in intracellular cyclic AMP (IC50 approximately 10(-9) M). ANP also stimulated breakdown of phosphatidylinositol phosphates and generation of inositol phosphates with a half-maximally effective concentration of approximately 10(-10) M. The extent of phosphatidylinositol polyphosphate hydrolysis was small (120%) in comparison to that of phosphatidylinositol (Ptd-Ins) (200%). Ptd-Ins hydrolysis was paralleled by the appearance of glycerophosphoinositol, and there was also a close temporal relationship between these processes and the accumulation of intracellular cyclic GMP. Smooth muscle cells released [3H]arachidonic acid label in response to ANP (EC50 approximately 10(-10) M). Taken together, the data suggest that the vasorelaxant hormone ANP has stimulatory effects on phosphoinositol lipid metabolism via both phospholipase C (generation of inositol phosphates) and phospholipase A2 (generation of releasable [3H]arachidonic acid and indirectly glycerophosphoinositol). In contrast, stimulation of phosphatidylinositol phosphate breakdown by the vasoconstrictive hormone angiotensin II is not associated with glycerophosphoinositol formation, and neither cyclic GMP nor cyclic AMP levels were influenced by this hormone.
在无细胞体系中，心房利钠肽（ANP）激活鸟苷酸环化酶的程度与全细胞中ANP刺激的环磷酸鸟苷（cGMP）水平之间存在差异，而且ANP的受体亲和力与剂量效力之间也存在差异。因此，我们研究了除受体偶联的鸟苷酸环化酶激活外，其他第二信使级联系统是否可能参与介导cGMP的增加以及对ANP的生理反应。对培养的胸主动脉平滑肌细胞进行的平衡125I-ANP结合研究显示存在低亲和力（约10^(-8) M，84.5 fmol/10^5细胞）和高亲和力（约10^(-10) M，12.5 fmol/10^5细胞）结合位点。我们证实ANP可升高细胞内cGMP（半数有效浓度[EC50]约为10^(-8) M），并抑制激动剂（异丙肾上腺素和福斯高林）诱导的细胞内环磷酸腺苷（cAMP）增加（半数抑制浓度[IC50]约为10^(-9) M）。ANP还刺激磷脂酰肌醇磷酸的分解和肌醇磷酸的生成，其半数最大有效浓度约为10^(-10) M。与磷脂酰肌醇（Ptd-Ins）的水解程度（200%）相比，磷脂酰肌醇多磷酸的水解程度较小（120%）。Ptd-Ins水解伴随着甘油磷酸肌醇的出现，并且这些过程与细胞内cGMP的积累之间也存在密切的时间关系。平滑肌细胞对ANP（EC50约为10^(-10) M）有反应而释放[3H]花生四烯酸标记物。综上所述，数据表明血管舒张激素ANP通过磷脂酶C（生成肌醇磷酸）和磷脂酶A2（生成可释放的[3H]花生四烯酸并间接生成甘油磷酸肌醇）对磷脂酰肌醇脂质代谢具有刺激作用。相比之下，血管收缩激素血管紧张素II对磷脂酰肌醇磷酸分解的刺激与甘油磷酸肌醇的形成无关，并且该激素对cGMP和cAMP水平均无影响。
