Leite M, Rouse D, Lederer E, Abramowitz J, Suki W N
Department of Medicine, Baylor College of Medicine, Houston, Texas.
Kidney Int. 1991 Sep;40(3):434-40. doi: 10.1038/ki.1991.230.
Both AVP and dDAVP effect a transient increase in cytosolic free calcium (iCa2+) in cortical collecting tubule (CCT) cells. To investigate the physiological role of this increase in iCa2+, we examined the effect of TMB-8, a putative inhibitor of iCa2+ release, on the initial and sustained phase of AVP- and dDAVP-stimulated water permeability (Pf) in isolated, perfused CCTs. Pretreatment of tubules with TMB-8, 50 microM, suppressed the increase in osmotic water permeability (Pf) induced by 10 microU/ml AVP and dDAVP, but had no effect on the sustained phase of the response. When increased to 100 microM. TMB-8 inhibited the sustained phase of AVP action. A similar pattern was observed on AVP-stimulated adenyly cyclase activity in rabbit renal membranes. Pretreatment of tubules with 50 microM TMB-8 attenuated the initial increase in Pf in response to cholera toxin but not to 8-Br-cAMP or forskolin. There was no effect of this concentration of TMB-8 on the sustained phase of these agonists. These studies suggest that, in lower concentrations, TMB-8 inhibits the mobilization of iCa2+, which is important for the interaction of Gs with the catalytic unit of adenylyl cyclase and the initial increase in AVP-stimulated Pf. In higher concentrations, TMB-8 inhibits adenylyl cyclase activity directly.
血管加压素（AVP）和去氨加压素（dDAVP）均可使皮质集合管（CCT）细胞胞质游离钙（iCa2+）短暂升高。为研究iCa2+升高的生理作用，我们检测了一种假定的iCa2+释放抑制剂——8-叔丁基-1,4-二甲基-2,6-二硝基苯（TMB-8）对分离灌注的CCT中AVP和dDAVP刺激的水通透性（Pf）初始阶段和持续阶段的影响。用50微摩尔/升的TMB-8预处理肾小管，可抑制10微单位/毫升AVP和dDAVP诱导的渗透水通透性（Pf）升高，但对反应的持续阶段无影响。当TMB-8浓度增至100微摩尔/升时，可抑制AVP作用的持续阶段。在兔肾膜中AVP刺激的腺苷酸环化酶活性上也观察到类似模式。用50微摩尔/升TMB-8预处理肾小管可减弱对霍乱毒素反应时Pf的初始升高，但对8-溴腺苷酸环化单磷酸（8-Br-cAMP）或福斯高林无此作用。该浓度的TMB-8对这些激动剂的持续阶段无影响。这些研究表明，较低浓度时，TMB-8抑制iCa2+的动员，这对Gs与腺苷酸环化酶催化单位的相互作用以及AVP刺激的Pf初始升高很重要。较高浓度时，TMB-8直接抑制腺苷酸环化酶活性。
