Kimura K, Nagai R, Sakai T, Aikawa M, Kuro-o M, Kobayashi N, Shirato I, Inagami T, Oshi M, Suzuki N
Second Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
Kidney Int. 1995 Aug;48(2):372-82. doi: 10.1038/ki.1995.305.
The contractility and distensibility of renal arterioles are important in the regulation of glomerular filtration. However, little is known regarding the characteristics of contractile proteins in these arterioles. Recently it was demonstrated that vascular smooth muscles contain two types of myosin heavy chain (MHC) isoforms, SM1 and SM2, which are unique molecular markers of smooth muscle cell phenotypes. SM1 is constitutively expressed in all types of smooth muscles, whereas SM2 exists only in mature smooth muscles. We characterized the expression of MHC isoforms as well as the ultrastructural myofilament assembly of renal arteriolar smooth muscles in human, rat and rabbit by immunohistochemical techniques. SM1 and alpha-smooth muscle actin were localized in both the preglomerular vessels (including the afferent arterioles) and efferent arterioles, whereas SM2 was present only in the preglomerular vessels. Renin-producing cells in the afferent arterioles (juxtaglomerular granular cells, JG cells) were positive for alpha-smooth muscle actin but negative for SM2. When renin synthesis was stimulated, the more proximal afferent arteriolar smooth muscles turned renin-positive and SM2 disappeared. Glomerular mesangial cells did not show immunoreactivities for SM1, SM2 or alpha-smooth muscle actin. The difference in MHC isoform expression in these arterioles was also reflected by ultrastructures; the afferent arteriolar smooth muscles contained abundant myofilaments including thick filaments, whereas the efferent arteriolar smooth muscles had a few myofilaments composed only of thin microfilaments. The JG cells displayed a myofilament assembly similar to that in the efferent arteriolar smooth muscles. We conclude from these observations that smooth muscles in pre-and postglomerular arterioles, the glomerular mesangial cells and JG cells differ in phenotypes, suggesting that they may have different contractile properties which may be critically involved in the regulation of glomerular filtration.
肾小动脉的收缩性和扩张性在肾小球滤过调节中起重要作用。然而，对于这些小动脉中收缩蛋白的特性了解甚少。最近有研究表明，血管平滑肌含有两种肌球蛋白重链（MHC）异构体，即SM1和SM2，它们是平滑肌细胞表型的独特分子标志物。SM1在所有类型的平滑肌中组成性表达，而SM2仅存在于成熟的平滑肌中。我们采用免疫组织化学技术，对人、大鼠和兔肾小动脉平滑肌中MHC异构体的表达以及超微结构的肌丝组装进行了表征。SM1和α-平滑肌肌动蛋白定位于肾小球前血管（包括入球小动脉）和出球小动脉，而SM2仅存在于肾小球前血管中。入球小动脉中的肾素产生细胞（球旁颗粒细胞，JG细胞）α-平滑肌肌动蛋白呈阳性，但SM2呈阴性。当肾素合成受到刺激时，更近端的入球小动脉平滑肌变为肾素阳性，且SM2消失。肾小球系膜细胞对SM1、SM2或α-平滑肌肌动蛋白均无免疫反应性。这些小动脉中MHC异构体表达的差异也反映在超微结构上；入球小动脉平滑肌含有丰富的肌丝，包括粗肌丝，而出球小动脉平滑肌只有少量仅由细肌微丝组成的肌丝。JG细胞的肌丝组装与出球小动脉平滑肌相似。我们从这些观察结果得出结论，肾小球前和肾小球后小动脉的平滑肌、肾小球系膜细胞和JG细胞在表型上存在差异，这表明它们可能具有不同的收缩特性，这些特性可能在肾小球滤过调节中起关键作用。
