Fenton Robert A, Poulsen Søren B, de la Mora Chavez Samantha, Soleimani Manoocher, Busslinger Meinrad, Dominguez Rieg Jessica A, Rieg Timo
InterPrET Center, Department of Biomedicine, Aarhus University, Aarhus, Denmark;
VA San Diego Healthcare System, San Diego, California;
Am J Physiol Renal Physiol. 2015 Jun 15;308(12):F1409-20. doi: 10.1152/ajprenal.00129.2015. Epub 2015 Apr 29.
Caffeine is one of the most widely consumed behavioral substances. We have previously shown that caffeine- and theophylline-induced inhibition of renal reabsorption causes diuresis and natriuresis, an effect that requires functional adenosine A1 receptors. In this study, we tested the hypothesis that blocking the Gi protein-coupled adenosine A1 receptor via the nonselective adenosine receptor antagonist caffeine changes Na(+)/H(+) exchanger isoform 3 (NHE3) localization and phosphorylation, resulting in diuresis and natriuresis. We generated tubulus-specific NHE3 knockout mice (Pax8-Cre), where NHE3 abundance in the S1, S2, and S3 segments of the proximal tubule was completely absent or severely reduced (>85%) in the thick ascending limb. Consumption of fluid and food, as well as glomerular filtration rate, were comparable in control or tubulus-specific NHE3 knockout mice under basal conditions, while urinary pH was significantly more alkaline without evidence for metabolic acidosis. Caffeine self-administration increased total fluid and food intake comparably between genotypes, without significant differences in consumption of caffeinated solution. Acute caffeine application via oral gavage elicited a diuresis and natriuresis that was comparable between control and tubulus-specific NHE3 knockout mice. The diuretic and natriuretic response was independent of changes in total NHE3 expression, phosphorylation of serine-552 and serine-605, or apical plasma membrane NHE3 localization. Although caffeine had no clear effect on localization of the basolateral Na(+)/bicarbonate cotransporter NBCe1, pretreatment with DIDS inhibited caffeine-induced diuresis and natriuresis. In summary, NHE3 is not required for caffeine-induced diuresis and natriuresis.
咖啡因是消费最为广泛的行为物质之一。我们之前已经表明，咖啡因和茶碱诱导的肾脏重吸收抑制会导致利尿和利钠，这一效应需要功能性腺苷A1受体。在本研究中，我们测试了以下假设：通过非选择性腺苷受体拮抗剂咖啡因阻断Gi蛋白偶联的腺苷A1受体会改变Na(+)/H(+)交换体亚型3（NHE3）的定位和磷酸化，从而导致利尿和利钠。我们构建了肾小管特异性NHE3基因敲除小鼠（Pax8-Cre），在这些小鼠中，近端小管S1、S2和S3节段以及厚壁升支中的NHE3丰度完全缺失或严重降低（>85%）。在基础条件下，对照或肾小管特异性NHE3基因敲除小鼠的液体和食物消耗量以及肾小球滤过率相当，而尿pH值明显更偏碱性，且无代谢性酸中毒迹象。不同基因型小鼠对咖啡因的自我给药增加的总液体和食物摄入量相当，饮用含咖啡因溶液的量无显著差异。通过口服灌胃急性给予咖啡因可引起利尿和利钠，对照和肾小管特异性NHE3基因敲除小鼠之间的这种效应相当。利尿和利钠反应与总NHE3表达的变化、丝氨酸-552和丝氨酸-605的磷酸化或顶端质膜NHE3的定位无关。尽管咖啡因对基底外侧Na(+)/碳酸氢根共转运体NBCe1的定位没有明显影响，但用二碘水杨酸（DIDS）预处理可抑制咖啡因诱导的利尿和利钠。总之，咖啡因诱导的利尿和利钠不需要NHE3参与。
