Mishima K, Kato J, Kuwasako K, Ito K, Imamura T, Kitamura K, Eto T
First Department of Internal Medicine, Miyazaki Medical College, 5200 Kihara, Kiyotake, Miyazaki 889-1692, Japan.
Biochem Biophys Res Commun. 2001 Sep 14;287(1):264-9. doi: 10.1006/bbrc.2001.5572.
Both endothelin (ET) and adrenomedullin (AM), produced by cardiac myocytes, are thought to be locally-acting hormones in the heart. Recently, calcitonin receptor-like receptor (CRLR) and receptor activity modifying proteins (RAMPs) have been shown to function together to serve as AM receptors stimulating cAMP production. In the present study, we examined the effects of ET on AM secretion, intracellular cAMP response to AM, and gene expressions of CRLR and RAMPs in cultured cardiac myocytes. Synthetic ET-1 dose-dependently increased AM secretion from the cardiomyocytes. AM increased the intracellular cAMP level in a dose-dependent manner and the cAMP accumulation by AM was significantly amplified by 24 h preincubation with ET-1. 10 nmol/L ET-1 significantly increased the CRLR mRNA level without any effect on RAMP1 mRNA. 1 micromol/L ET-1 significantly reduced the RAMP2 mRNA level, but ET-1 dose-dependently increased the RAMP3 mRNA level in the cardiac myocytes. These findings suggest that ET-1 not only stimulates AM secretion, but also modulates intracellular cAMP responses to AM probably by altering the expressions of CRLR and RAMPs in rat cardiomyocytes.
心肌细胞产生的内皮素（ET）和肾上腺髓质素（AM）被认为是心脏中的局部作用激素。最近，降钙素受体样受体（CRLR）和受体活性修饰蛋白（RAMP）已被证明共同发挥作用，作为刺激cAMP产生的AM受体。在本研究中，我们检测了ET对培养心肌细胞中AM分泌、细胞内对AM的cAMP反应以及CRLR和RAMP基因表达的影响。合成的ET-1剂量依赖性地增加了心肌细胞的AM分泌。AM以剂量依赖性方式增加细胞内cAMP水平，并且通过与ET-1预孵育24小时，AM引起的cAMP积累显著放大。10 nmol/L ET-1显著增加CRLR mRNA水平，而对RAMP1 mRNA无任何影响。1 μmol/L ET-1显著降低RAMP2 mRNA水平，但ET-1剂量依赖性地增加心肌细胞中RAMP3 mRNA水平。这些发现表明，ET-1不仅刺激AM分泌，还可能通过改变大鼠心肌细胞中CRLR和RAMP的表达来调节细胞内对AM的cAMP反应。
