Di Sole Francesca, Cerull Robert, Petzke Soeren, Casavola Valeria, Burckhardt Gerhard, Helmle-Kolb Corinna
Department of Physiology and Pathophysiology, Division of Vegetative Physiology and Pathophysiology, Georg-August University of Goettingen, Humboldtallee 23, D-37073 Goettingen, Germany.
J Am Soc Nephrol. 2003 Jul;14(7):1720-30. doi: 10.1097/01.asn.0000072743.97583.db.
Regulation of renal apical Na+/H+ exchanger 3 (NHE3) activity by adenosine has been suggested to contribute to acute control of mammalian Na(+) homeostasis. The mechanism by which adenosine controls NHE3 activity in a renal cell line was examined. The adenosine analog, N(6)-cyclopentyladenosine (CPA) exerts a bimodal effect on NHE3: CPA concentrations >10(-8) M inactivate NHE3, whereas concentrations <10(-8) M stimulate NHE3 activity. Acute CPA-induced control of NHE3 was blocked by antagonists of A1 adenosine receptors and inhibition of phospholipase C, pretreatment with BAPTA-AM (chelator of cellular calcium), and exposure to pertussis toxin. Stimulatory and to some extent also inhibitory CPA concentrations attenuated 8-bromo-cAMP and dopamine-mediated inhibition of NHE3. BAPTA eliminated the ability of a stimulatory dose of CPA to attenuate 8-bromo-cAMP-induced suppression of NHE3 activity. Upon inhibition of protein kinase C, CPA at an inhibitory dose provoked activation of NHE3, which is partially reverted by 8-bromo-cAMP and suppressed by pre-incubation with BAPTA-AM. Cytochalasin B, an actin-modifying agent, selectively prevented downregulation but did not affect upregulation of NHE3 activity by CPA. In conclusion, these observations demonstrate that (1) CPA modulates NHE3 activity by elevation of cellular Ca(2+) exerting a negative control on adenylate cyclase activity, (2) protein kinase C is the determining factor leading to CPA-induced downregulation of NHE3 activity, and (3) alterations of surface NHE3 abundance may contribute to A1 adenosine receptor-dependent inhibition of NHE3 activity.
腺苷对肾顶端钠/氢交换体3（NHE3）活性的调节被认为有助于哺乳动物钠稳态的急性控制。研究了腺苷在肾细胞系中控制NHE3活性的机制。腺苷类似物N(6)-环戊基腺苷（CPA）对NHE3有双峰效应：CPA浓度>10(-8) M时使NHE3失活，而浓度<10(-8) M时刺激NHE3活性。急性CPA诱导的NHE3控制被A1腺苷受体拮抗剂、磷脂酶C抑制、BAPTA-AM（细胞钙螯合剂）预处理以及百日咳毒素处理所阻断。刺激剂量的CPA以及在一定程度上抑制剂量的CPA减弱了8-溴-cAMP和多巴胺介导的NHE3抑制。BAPTA消除了刺激剂量的CPA减弱8-溴-cAMP诱导的NHE3活性抑制的能力。抑制蛋白激酶C后，抑制剂量的CPA可引发NHE3的激活，8-溴-cAMP可部分逆转这种激活，而BAPTA-AM预孵育可抑制这种激活。细胞松弛素B是一种肌动蛋白修饰剂，可选择性地阻止NHE3活性的下调，但不影响CPA对NHE3活性的上调。总之，这些观察结果表明：（1）CPA通过升高细胞内Ca(2+)来调节NHE3活性，对腺苷酸环化酶活性产生负调控；（2）蛋白激酶C是导致CPA诱导NHE3活性下调的决定性因素；（3）表面NHE3丰度的改变可能有助于A1腺苷受体依赖性的NHE3活性抑制。
