Horiuchi A, Albrecht F E, Eisner G M, Jose P A, Felder R A
Department of Pathology, University of Virginia Medical Center, Charlottesville 22908.
Am J Physiol. 1992 Dec;263(6 Pt 2):F1105-11. doi: 10.1152/ajprenal.1992.263.6.F1105.
We have reported defective coupling of the renal tubular DA1 dopamine receptor to adenylyl cyclase in both the spontaneously hypertensive rat (SHR) and the Dahl salt-sensitive rat. Since Na+, 5'-guanyl imidodiphosphate [Gpp(NH)p], and N-ethylmaleimide (NEM) reduce agonist affinity for brain D1 dopamine receptors, we compared the effects of these agents on agonist affinity in proximal tubules from SHR and its normotensive control, the Wistar-Kyoto rat (WKY), to delineate further the site of the DA1-adenylyl cyclase coupling defect. In WKY, the D1/DA1 agonist, fenoldopam, competed for 125I-Sch 23982 at a high-affinity site (KiH = 1.8 +/- 0.8 x 10(-8) M) and a low-affinity site (KiL = 7.6 +/- 1.1 x 10(-5) M, n = 6). Na+ (150 mM) or Gpp(NH)p (10(-4) M) converted KiH to KiL. NEM, which alkylates sulfhydryl groups, also converted all the binding to KiL; this effect could be prevented by prior treatment with 10(-4) M fenoldopam. In contrast, in SHR, fenoldopam detected only a KiL (7.8 +/- 1.4 x 10(-5) M, n = 6). Neither Na+, Gpp(NH)p, nor NEM had any effect on KiL. To study a functional expression of these binding sites, the effect of 5 x 10(-5) M fenoldopam or 8-(chlorophenylthio)-adenosine 3',5'-cyclic monophosphate (8-CPT-cAMP) on Na+/H+ exchange activity in proximal tubular brush-border membrane vesicles was tested. In WKY, the inhibitory effects of these agents on the exchanger increased with the age of the rat.(ABSTRACT TRUNCATED AT 250 WORDS)
我们已经报道了在自发性高血压大鼠（SHR）和 Dahl 盐敏感大鼠中，肾小管 DA1 多巴胺受体与腺苷酸环化酶的偶联存在缺陷。由于 Na⁺、5'-鸟苷亚胺二磷酸 [Gpp(NH)p] 和 N-乙基马来酰亚胺（NEM）会降低激动剂对脑 D1 多巴胺受体的亲和力，我们比较了这些试剂对 SHR 及其正常血压对照 Wistar-Kyoto 大鼠（WKY）近端小管中激动剂亲和力的影响，以进一步确定 DA1-腺苷酸环化酶偶联缺陷的位点。在 WKY 中，D1/DA1 激动剂非诺多泮在高亲和力位点（KiH = 1.8 ± 0.8 × 10⁻⁸ M）和低亲和力位点（KiL = 7.6 ± 1.1 × 10⁻⁵ M，n = 6）与¹²⁵I-Sch 23982 竞争。Na⁺（150 mM）或 Gpp(NH)p（10⁻⁴ M）将 KiH 转变为 KiL。使巯基烷基化的 NEM 也将所有结合转变为 KiL；用 10⁻⁴ M 非诺多泮预先处理可防止这种作用。相反，在 SHR 中，非诺多泮仅检测到一个 KiL（7.8 ± 1.4 × 10⁻⁵ M，n = 6）。Na⁺、Gpp(NH)p 或 NEM 对 KiL 均无任何影响。为了研究这些结合位点的功能表达，测试了 5 × 10⁻⁵ M 非诺多泮或 8-（氯苯硫基）-腺苷 3',5'-环一磷酸（8-CPT-cAMP）对近端小管刷状缘膜囊泡中 Na⁺/H⁺交换活性的影响。在 WKY 中，这些试剂对交换体的抑制作用随大鼠年龄增加而增强。（摘要截短于 250 字）
