Girardi Adriana Castello Costa, Fukuda Lívia Emy, Rossoni Luciana Venturini, Malnic Gerhard, Rebouças Nancy Amaral
Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo, São Paulo, SP, Brazil.
Am J Physiol Renal Physiol. 2008 Feb;294(2):F414-22. doi: 10.1152/ajprenal.00174.2007. Epub 2007 Dec 12.
In the microvillar microdomain of the kidney brush border, sodium hydrogen exchanger type 3 (NHE3) exists in physical complexes with the serine protease dipeptidyl peptidase IV (DPPIV). The purpose of this study was to explore the functional relationship between NHE3 and DPPIV in the intact proximal tubule in vivo. To this end, male Wistar rats were treated with an injection of the reversible DPPIV inhibitor Lys [Z(NO2)]-pyrrolidide (I40; 60 mg.kg(-1).day(-1) ip) for 7 days. Rats injected with equal amounts of the noninhibitory compound Lys[Z(NO2)]-OH served as controls. Na(+) - H(+) exchange activity in isolated microvillar membrane vesicles was 45 +/- 5% decreased in rats treated with I40. Membrane fractionation studies using isopycnic centrifugation revealed that I40 provoked redistribution of NHE3 along with a small fraction of DPPIV from the apical enriched microvillar membranes to the intermicrovillar microdomain of the brush border. I40 significantly increased urine output (67 +/- 9%; P < 0.01), fractional sodium excretion (63 +/- 7%; P < 0.01), as well as lithium clearance (81 +/- 9%; P < 0.01), an index of end-proximal tubule delivery. Although not significant, a tendency toward decreased blood pressure and plasma pH/HCO(3)(-) was noted in I40-treated rats. These findings indicate that inhibition of DPPIV catalytic activity is associated with inhibition of NHE3-mediated NaHCO3 reabsorption in rat renal proximal tubule. Inhibition of apical Na(+) - H(+) exchange is due to reduced abundance of NHE3 protein in the microvillar microdomain of the kidney brush border. Moreover, this study demonstrates a physiologically significant interaction between NHE3 and DPPIV in the intact proximal tubule in vivo.
在肾刷状缘的微绒毛微区，3型钠氢交换体（NHE3）与丝氨酸蛋白酶二肽基肽酶IV（DPPIV）以物理复合物的形式存在。本研究的目的是探讨在完整的近端小管体内NHE3与DPPIV之间的功能关系。为此，给雄性Wistar大鼠注射可逆性DPPIV抑制剂Lys [Z(NO2)] - 吡咯烷（I40；60 mg·kg⁻¹·天⁻¹，腹腔注射），持续7天。注射等量非抑制性化合物Lys[Z(NO2)] - OH的大鼠作为对照。用I40处理的大鼠分离的微绒毛膜囊泡中的Na⁺ - H⁺交换活性降低了45±5%。使用等密度离心的膜分级研究表明，I40促使NHE3以及一小部分DPPIV从富含顶端的微绒毛膜重新分布到刷状缘的微绒毛间微区。I40显著增加尿量（67±9%；P < 0.01）、钠排泄分数（63±7%；P < 0.01）以及锂清除率（81±9%；P < 0.01），锂清除率是近端小管末端输送的指标。虽然不显著，但在I40处理的大鼠中观察到血压和血浆pH/HCO₃⁻有下降趋势。这些发现表明，DPPIV催化活性的抑制与大鼠肾近端小管中NHE3介导的NaHCO₃重吸收的抑制有关。顶端Na⁺ - H⁺交换的抑制是由于肾刷状缘微绒毛微区中NHE3蛋白丰度降低。此外，本研究证明了在完整的近端小管体内NHE3与DPPIV之间存在生理上显著的相互作用。
