Amino Acid Sensing by Enteroendocrine STC-1 Cells: Role of the Na+- Coupled Neutral Amino Acid Transporter 2 (Snat2)

STEVEN H YOUNG; OSVALDO REY; CATIA STERNINI; ENRIQUE ROZENGURT

Congreso; Digestive Diseases Week; 2010

AGA

Background: Amino acids have been known for many years to regulate GI functions via the release of gastrointestinal hormones from enteroendocrine cells. It is increasingly recognized that amino acids are sensed in the GI tract by a variety of recently identified receptors and transporters, but the precise mechanisms involved remain incompletely understood. The experiments presented here were designed to define the molecular pathway(s) by which externally applied amino acids can initiate Ca2+ signaling in enteroendocrine STC-1 cells. Results: Our results show that STC-1 cells, a model of intestinal endocrine cells, respond to a broad range of amino acids, including L-proline, L-serine, L-alanine, L-methionine, L- gycine, L-histidine and 〈-methyl-amino-isobutyric acid (MeAIB) with a rapid increase in the intracellular Ca2+concentration ([Ca2+]i). We sought to identify the mechanism by which amino acids induce Ca2+ signaling in these cells. We produced several lines of evidence suggesting that amino acid transport through the Na+-coupled neutral amino acid transporter 2 (SNAT2) is a major mechanism by which amino acids induced Ca2+ signaling in STC-1 cells: 1) the amino acid efficacy profile for inducing Ca2+ signaling in STC-1 cells, closely matches the amino acid specificity of SNAT2; 2) amino acid-induced Ca2+ signaling in STC-1 cells was suppressed by removing Na+ from the medium; 3) the non-metabolized synthetic substrate of amino acid transport MeAIB produced a marked increase in [Ca2+]i; 4) transfection of siRNA targeting SNAT2 produced a marked decrease in Ca2+ signaling in response to L-proline in STC-1 cells; 5) amino acid-induced increase in [Ca2+]i was associated with membrane depolarization and mediated by Ca2+ influx since it depended on extracellular Ca2+; 6) the increase in [Ca2+]i in response to L-proline, L-alanine or MeAIB was abrogated by nifedipine, which blocks L-type voltage-sensitive Ca2+ channels (VSCCs).