Zsembery A, Spirlì C, Granato A, LaRusso N F, Okolicsanyi L, Crepaldi G, Strazzabosco M
Institute of Internal Medicine and Azienda Ospedaliera di Padova, University of Padova, Padova, Italy.
Hepatology. 1998 Oct;28(4):914-20. doi: 10.1002/hep.510280403.
Biliary epithelial cells (cholangiocytes) are responsible for rapid regulation of bile volume and alkalinity. Secretin and other hormones raising intracellular cyclic adenosine monophosphate (cAMP) concentrations promote biliary HCO3 secretion by stimulating apical Cl- channels and Cl-/HCO3- exchange (AE2). Cholangiocyte ion transport may also be stimulated by locally acting mediators; for example, adenosine 5'-triphosphate (ATP), a secretagogue that can be released into the bile by hepatocytes and cholangiocytes, activates Cl- conductances and Na+/H+ exchange (NHE) in cholangiocyte cell lines. To further explore the role of extracellular ATP in the paracrine regulation of carrier mechanisms regulating cholangiocyte H+/HCO3- secretion, we investigated the effects of nucleotides on intracellular pH regulation (measured by microfluorimetry with 2'7'-bis(2-carboxyethyl)-5,6,carboxyfluorescein [BCECF]) in human (MZ-ChA-1) and rat (NRC-1) cholangiocyte cell lines. In MZ-ChA-1 cells, 10 mol/L ATP, uridine 5'-triphosphate (UTP), and ATPgammas significantly increased NHE activity. The pharmacological profile of agonists was consistent with that anticipated for receptors of the P2Y2 class. ATP did not increase AE2 activity, but, when given to cells pretreated with agents raising intracellular cAMP, had a synergistic stimulatory effect that was inhibited by amiloride. To assess the polarity of purinergic receptors, monolayers of NRC-1 cells were exposed to apical or basolateral nucleotides. Apical administration of purinergic agonists, but not adenosine, increased basolateral NHE activity (ATPgammaS > UTP > ATP). Basolateral administration of purinergic agonists induced a weaker activation of NHE, which was instead strongly stimulated by adenosine and by adenosine receptor agonists (NECA = R-PIA = S-PIA). In conclusion, this study demonstrates that, consistent with the proposed role for biliary ATP in paracrine and autocrine control of cholangiocyte ion secretion, extracellular ATP stimulates cholangiocyte basolateral NHE activity through P2Y2 receptors that are predominantly expressed at the apical cell membrane.
胆管上皮细胞（胆管细胞）负责胆汁量和碱度的快速调节。促胰液素和其他能提高细胞内环磷酸腺苷（cAMP）浓度的激素，通过刺激顶端氯离子通道和氯离子/碳酸氢根离子交换（AE2）促进胆管碳酸氢根分泌。胆管细胞离子转运也可能受到局部作用介质的刺激；例如，三磷酸腺苷（ATP），一种可由肝细胞和胆管细胞释放到胆汁中的促分泌素，可激活胆管细胞系中的氯离子电导和钠/氢交换（NHE）。为了进一步探讨细胞外ATP在旁分泌调节胆管细胞氢离子/碳酸氢根分泌载体机制中的作用，我们研究了核苷酸对人（MZ-ChA-1）和大鼠（NRC-1）胆管细胞系细胞内pH调节的影响（用2'7'-双（2-羧乙基）-5,6-羧基荧光素[BCECF]通过微量荧光测定法测量）。在MZ-ChA-1细胞中，10 μmol/L的ATP、尿苷三磷酸（UTP）和ATPγS显著增加NHE活性。激动剂的药理学特征与预期的P2Y2类受体一致。ATP不会增加AE2活性，但当给予用提高细胞内cAMP的药物预处理的细胞时，具有协同刺激作用，该作用被阿米洛利抑制。为了评估嘌呤能受体的极性，将NRC-1细胞单层暴露于顶端或基底外侧核苷酸。顶端给予嘌呤能激动剂而非腺苷可增加基底外侧NHE活性（ATPγS > UTP > ATP）。基底外侧给予嘌呤能激动剂诱导的NHE激活较弱，而腺苷和腺苷受体激动剂（NECA = R-PIA = S-PIA）则强烈刺激NHE。总之，本研究表明，与胆汁ATP在旁分泌和自分泌控制胆管细胞离子分泌中的作用一致，细胞外ATP通过主要表达于顶端细胞膜的P2Y2受体刺激胆管细胞基底外侧NHE活性。
