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

胃黏膜分泌消化性盐酸和胃蛋白酶，与饮食摄入相协调。尽管壁细胞分泌HCl已是公认的事实，但越来越多的证据表明，当壁细胞向下迁移到胃腺体的颈部和底部时，这些细胞经历了重大的形态、生化和功能变化。这些变化的性质和功能意义尚不清楚。我们发现壁细胞转化包括分泌Na-K-2Cl共转运体（NKCC）的突然和惊人的表达。迁移相关的NKCC表达与Cl/HCO3交换剂（AE2）和H、k - atp酶活性的损失以及水通道蛋白-4的表达在拓扑上相关。我们假设向下迁移的壁细胞可能经历了其主要功能从酸性氯化物（HCl）分泌到非酸性氯化物（NaCl）分泌的程序性转换。腺体底部的壁细胞分泌的生理盐水体积可能有助于冲洗局部胃蛋白酶原和远端酸的管腔。这里提出的项目包括四个互补的研究。目的1将通过离体胃腺的显微荧光成像，确定壁细胞迁移过程中NKCC表达和AE2丢失对细胞内Cl-稳态和载体Cl-运输的功能影响。目的2将开始描述在体外和体内基底壁细胞中调节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先前的证据所表明的那样，不再发挥强大的酸分泌功能。最后，Aim 4将绘制K- cl共转运体-1 （KCC1）在胃粘膜的细胞和亚细胞分布，并开始评估K- cl共转运体-1 （KCC1）可能有助于顶壁细胞的顶端K+再循环的可能性。完成这些目标将开始澄清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.