FUNCTION & REGULATION OF GASTRIC NA/K/2CL COTRANSPORTERS

胃粘膜分泌消化的盐酸和胃酶，与饮食摄入量相协调。虽然壁细胞分泌HCl现在是不言而喻的，但越来越多的证据表明，当这些细胞向下迁移到胃腺的颈部和底部时，它们会经历重大的形态、生化和功能变化。人们对这些变化的性质和功能意义知之甚少。我们发现，壁细胞的转化包括分泌型Na-K-2Cl协转运蛋白(NKCC)的突然和大量表达。NKCC的迁移相关表达与Cl/HCO3交换(AE2)和H，K-ATPase活性的丧失以及水通道蛋白-4的表达密切相关。我们推测，向下迁移的壁细胞可能经历了其主要功能的程序性转换，从酸性氯化物(HCl)分泌到非酸性氯化物(氯化钠)分泌。腺体底部的壁细胞分泌的盐水量可能用于冲洗局部胃蛋白酶原和远端酸的管腔。这里提出的项目由四项互补性研究组成。目的1通过分离胃腺的显微荧光成像，确定NKCC表达和AE2缺失在壁细胞迁移过程中对细胞内氯离子稳态和载体氯离子转运的功能影响。目的2将在体外和体内研究调节NKCC的信号、受体和细胞内介质。Aim 3将直接测试腺体底部的壁细胞是否像以前的证据所表明的那样，停止作为强健的酸性分泌物发挥作用。最后，Aim 4将绘制胃粘膜中K-Cl共转运体-1(KCC1)的细胞和亚细胞分布图，并开始评估K-Cl共转运体-1(KCC1)可能有助于壁细胞顶端K+循环。这些目标的完成将开始阐明与迁移相关的壁细胞分化的功能后果。

The gastric mucosa secretes digestive hydrochloric acid and pepsin in coordination with dietary intake. Although it is now axiomatic that parietal cells secrete HCl, a growing body of evidence indicates that these cells undergo major morphological, biochemical, and functional changes as they migrate down into the neck and base of the gastric gland. The nature and functional significance of these changes are poorly understood. We show that parietal cell transformation includes a sudden and prodigious expression of the secretory Na-K-2Cl cotransporter (NKCC). The migration-associated expression of NKCC is topologically correlated with loses of Cl/HCO3 exchanger (AE2) and H,K-ATPase activity, and with expression of aquaporin-4 water channels. We hypothesize that downwardly-migrating parietal cells might undergo a programmed conversion of their principal function from acidic chloride (HCl) secretion to nonacidic chloride (NaCl) secretion. The secretion of a saline fluid volume by parietal cells in the base of the gland might serve to flush the lumen of local pepsinogen and distal acid. The project proposed here consists of four complementary studies. Aim 1 will determine the functional consequences of NKCC expression and AE2 loss during parietal cell migration on intracellular Cl- homeostasis and vectorial Cl- transport by microspectrofluorometric imaging of isolated gastric glands. Aim 2 will begin to delineate the signals, receptors, and intracellular mediators that regulate NKCC in basilar parietal cells in vitro and in vivo. Aim 3 will directly test whether parietal cells in the gland base cease to function as robust acid secretors, as previous evidence has suggested. Finally, Aim 4 will map the cellular and subcellular distribution of K-Cl cotransporter-1 (KCC1) in gastric mucosa and begin to assess the possibility that K-Cl cotransporter-1 (KCC1) may contribute to apical K+ recycling in parietal cells. Completion of these aims will begin to clarify the functional consequences of the migration-associated differentiation of parietal cells.