Cantau B, Guillon G, Alaoui M F, Chicot D, Balestre M N, Devilliers G
Centre National de la Recherche Scientifique-Institut National de la Santé et de la Recherche Médicale de Pharmacologie-Endocrinologie, Montpellier, France.
J Biol Chem. 1988 Jul 25;263(21):10443-50.
The exposure of WRK1 cells to arginine vasopressin (AVP), lysine vasopressin, or oxytocin for 18 h at 37 degrees C induced a homologous desensitization of the vasopressin- (VP) receptors. Dose-response curves of [3H]lysine vasopressin binding to control and desensitized WRK1 cells revealed a decrease in the maximal number of binding sites without any modification of its affinity (Kd values = 4.40 +/- 0.76 nM and 4.65 +/- 0.78 nM for control and desensitized conditions, respectively). The phenomenon was time- and dose-dependent. It was directly related to receptor occupancy, since the concentration of VP analogues leading to a half-maximal occupancy of VP receptors was closely related to the concentration of the corresponding analogue leading to a half-maximal decrease in VP-binding sites. It was also agonist-specific, since the V1 vasopressin antagonist desGly9d(CH2)5[D-Tyr(Et)2]VAVP was unable to affect the number of receptors. These desensitization processes were completely inhibited when the functional coated pits present in WRK1 cells were suppressed, indicating that the loss of VP-binding sites was related to receptor internalization. The exposure of WRK1 cells to a vasopressin agonist for 18 h also led to an inhibition of the vasopressin-sensitive phospholipase C activity. It was time- and agonist-dose-dependent, and occurred without any detectable changes in apparent affinity values (1.40 +/- 0.04 and 1.90 +/- 0.36 nM for control and desensitized cells, respectively). Control experiments showed that these inhibitions could not have been caused by a decrease in the labeling of inositol lipids. It is likely that they were mainly due to receptor internalization since (i) the hormonal treatment did not modify the basal level of phospholipase C; (ii) the maximal loss of VP-binding site was similar to the maximal inhibition of VP-stimulated IP accumulation; (iii) the recoveries of both VP-binding sites and VP-sensitive phospholipase C activity followed exactly the same time course (t1/2 = 4 h). In addition to this homologous desensitization of VP-sensitive phospholipase C activity, AVP also induced heterologous desensitization of bradykinin-sensitive phospholipase C activity. However, this effect was relatively weak (maximal inhibition 17 +/- 3%). The time course of VP-sensitive phospholipase C desensitization was more rapid than that of VP-receptors, indicating that desensitization involved at least two distinct steps, a rapid uncoupling step, and a later loss of vasopressin receptors.(ABSTRACT TRUNCATED AT 400 WORDS)
在37℃下将WRK1细胞暴露于精氨酸加压素（AVP）、赖氨酸加压素或催产素18小时，可诱导加压素（VP）受体的同源脱敏。[3H]赖氨酸加压素与对照和脱敏WRK1细胞结合的剂量反应曲线显示，结合位点的最大数量减少，但其亲和力未发生任何改变（对照和脱敏条件下的Kd值分别为4.40±0.76 nM和4.65±0.78 nM）。该现象具有时间和剂量依赖性。它与受体占据直接相关，因为导致VP受体占据率达到半数最大值时VP类似物的浓度，与导致VP结合位点减少半数最大值时相应类似物的浓度密切相关。它也是激动剂特异性的，因为V1加压素拮抗剂去甘氨酸9 - d(CH2)5[D - 酪氨酸（乙基）2]VAVP无法影响受体数量。当WRK1细胞中存在的功能性包被小窝被抑制时，这些脱敏过程被完全抑制，表明VP结合位点的丧失与受体内化有关。将WRK1细胞暴露于加压素激动剂18小时还导致对加压素敏感的磷脂酶C活性受到抑制。它具有时间和激动剂剂量依赖性，并且在表观亲和力值上没有任何可检测到的变化（对照细胞和脱敏细胞的表观亲和力值分别为1.40±0.04和1.90±0.36 nM）。对照实验表明，这些抑制作用不可能是由肌醇脂质标记减少引起的。它们可能主要是由于受体内化，因为（i）激素处理未改变磷脂酶C的基础水平；（ii）VP结合位点的最大丧失与VP刺激的肌醇磷酸积累的最大抑制相似；（iii）VP结合位点和VP敏感的磷脂酶C活性的恢复遵循完全相同的时间进程（t1/2 = 4小时）。除了这种对VP敏感的磷脂酶C活性的同源脱敏外，AVP还诱导了对缓激肽敏感的磷脂酶C活性的异源脱敏。然而，这种作用相对较弱（最大抑制率为17±3%）。VP敏感的磷脂酶C脱敏的时间进程比VP受体的更快，表明脱敏至少涉及两个不同的步骤，一个快速解偶联步骤和一个后期加压素受体的丧失。（摘要截断于400字）
