Expression of acid-sensing ion channels in intestinal epithelial cells and their novel role in the regulation of duodenal mucosal bicarbonate secretion

摘要

Although acid-sensing ion channels (ASICs) have been studied in a variety of mammalian cells, little is currently known about their presence in intestinal epithelial cells. Therefore, the aims of the present study were to investigate the expression and function of ASIC isoforms in intestinal epithelial cells, particularly their physiological role in the acid-stimulated duodenal mucosal bicarbonate secretion (DMBS). RT-PCR and digital Ca²⁺ imaging were used to determine the expression and function of ASICs in HT29 cells, a human intestinal epithelial cell line. The acid-stimulated DMBS was measured in C57 black mice in vivo to study the role of ASICs in this physiological process. mRNA expression of ASIC1a was detected in the duodenal mucosa stripped from mice and HT29 cells, in which cytoplasmic free Ca²⁺ ([Ca²⁺]cyt) in response to extracellular acidosis was also measured. In Ca²⁺-containing solutions, acidosis raised [Ca²⁺]cyt in a pH-dependent manner with a half-maximal effect (pH0.5) at approximately 5.9. The acidosis-induced increase in [Ca²⁺]cyt was markedly inhibited by amiloride (an ASIC blocker), SK&F96365 (a blocker for non-selective cation channels), or in Ca²⁺-free solutions; but slightly affected by , or nifedipine. After acidosis raised [Ca²⁺]cyt, stimulation of purinergic receptors with ATP further increased [Ca²⁺]cyt. Moreover, the acid-stimulated murine DMBS was significantly attenuated by amiloride. Therefore, ASIC1a is functionally expressed in intestinal epithelial cells, and may play an important role in the regulation of [Ca²⁺]cyt homeostasis in these cells and the acid-stimulated DMBS.