Molecular mechanisms of chronic pancreatitis : Ethanol-induced dysfunction of ion channels

1.为探讨HCO_3^-的分泌机制，我们测定了离体豚鼠胰腺小叶间导管微灌注细胞内HCO_3^-（[HCO_3^-]_i）和Cl^-（[Cl^-]_i）的跨膜浓度。在cAMP刺激下，当腔中HCO_3^-浓度升高到125 mM（24 mM Cl^-）时，pH_i没有升高到7.2以上（[HCO_3^-]_i = 120 mM），表明腔中Cl^--HCO_3^-交换受到抑制。在相同条件下，[Cl^-]_i保持在很低的水平，约为0.7mM，这将有利于HCO_3^-_i通过管腔阴离子电导的分泌. 5-羟色胺（5-HT，5-羟色胺）在0. 1μM通过5-HT_3受体强烈抑制离体导管的液体分泌。该作用是通过Na^+-HCO_3^-共转运抑制基底外侧HCO_3 ^-蓄积介导的。胰腺导管肠嗜铬细胞释放的5-HT可能以旁分泌方式调节液体分泌. RT-PCR和免疫组化显示，AQP 1在导管细胞的表达。无论是基底侧或管腔内应用HgCl_2，导管上皮的渗透水渗透性均降低80-90%。已知的水通道AQP 1似乎是胰腺导管上皮的主要水通道.虽然酒精滥用是急性和慢性胰腺炎最常见的原因，但酒精导致疾病的机制尚不清楚。偶尔社交饮酒后观察到的1 mM乙醇浓度显著增加了液体分泌的最大速率，并诱导分泌素或二丁酰cAMP刺激的导管内细胞内Ca^2+浓度短暂增加。当蛋白质栓或结石干扰胰液流动时，乙醇引起的液体分泌过多会使近端管内压力升高，导致水肿形成或胰腺炎。

1. To investigate the secretory mechanism of HCO_3^-, across the luminal membrane of pancreatic duct cell we have measured intracellular concentrations of HCO_3^- ([HCO_3^-]_i) and of Cl^- ([Cl^-]_i) in microperfused interlobular duct segments isolated from guinea-pig pancreas. When the HCO_3^- concentration in the lumen was raised to 125 mM (24 mM Cl^-) under cAMP stimulation, pH_i did not increase above 7.2 ([HCO_3^-]_i = 〜 20 mM), indicating that luminal Cl^--HCO_3^- exchange was inhibited. Under the same condition, [Cl^-]_i was kept very low at 〜7 mM, which would tend to favor HCO_3^-' secretion via a luminal anion conductance.2. 5-hydroxytryptamine (5-HT, serotonin) at 0. 1μM strongly inhibited fluid secretion in isolated ducts via 5-HT_3 receptor. The action is mediated by the inhibition of basolateral HCO_3^- accumulation via Na^+-HCO_3^- cotransport. 5-HT released from pancreatic ductal enterochromaffin cells may regulate fluid secretion in a paracrine fashion.3. RT-PCR analysis and immunohistochemistry of isolated ducts revealed the expression of AQP1 in duct cells. The osmotic water permeability of the ductal epithelium was reduced by 80-90% with either basolateral or luminal application of HgCl_2. AQP1 of the known water channels appears to be the main water pathway in pancreatic ductal epithelium.4. Although ethanol abuse is the most common cause of acute and chronic pancreatitis, the mechanism by which ethanol causes the disease is not well understood. Ethanol at 1 mM, the concentration observed after an occasional social drinking, significantly augmented the maximal rate of fluid secretion and induced a transient increase in intracellular Ca^<2+> concentration in ducts stimulated with secretin or dibutyryl cAMP. When the flow of pancreatic juice is disturbed by protein plug or stones, fluid hypersecretion induced by ethanol would elevate the intraductal pressure in the proximal part of the duct, leading to edema formation or pancreatitis.