Interstitial cells of Cajal (ICC) generate electrical slow waves, which are required for normal gastrointestinal motility. The mechanisms for generation of normal pacemaking are not fully understood. Normal gastrointestinal contractility and electrical slow wave activity depend on the presence of extracellular HCO₃^-. Previous transcriptional analysis identified enrichment of mRNA encoding the electrogenic Na⁺/HCO₃^- cotransporter (NBCe1) gene (Slc4a4) in pacemaker myenteric ICC in mouse small intestine. We aimed to determine the distribution of NBCe1 protein in ICC of the mouse gastrointestinal tract, and to identify the transcripts of the Slc4a4 gene in mouse and human small intestinal tunica muscularis. We determined the distribution of NBCe1-immunoreactivity (NBCe1-IR) by immunofluorescent labeling in mouse and human tissues. In mice, NBCe1-IR was restricted to Kit-positive myenteric ICC of the stomach and small intestine and sub-muscular ICC of the large intestine; that is the slow wave generating subset of ICC. Other sub-types of ICC were NBCe1-negative. Quantitative real time PCR identified >500 fold enrichment of Slc4a4‑207 and Slc4a4‑208 transcripts (IP3-receptor binding protein released by IP3" (IRBIT) regulated isoforms) in Kit expressing cells isolated from Kit^creERT2/+, Rpl22^tm1.1Psam/Sj mice and from single GFP-positive ICC from Kit^tm1Rosay mice. Human jejunal tunica muscularis ICC were also NBCe1-positive and SLC4A4‑201 and SLC4A4‑204 RNAs were >300 fold enriched relative to SLC4A4‑202. In summary, NBCe1 protein expressed in ICC with electrical pacemaker function is encoded by Slc4a4 gene transcripts that generate IRBIT regulated isoforms of NBCe1. In conclusion Na⁺/HCO₃^- cotransport through NBCe1 contributes to the generation of pacemaker activity in subsets of ICC.

中文翻译：

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Cajal 的起搏器间质细胞中富含电生 Na+/HCO3-协同转运蛋白 NBCe1 的调节同种型的表达

Cajal (ICC) 间质细胞产生电慢波，这是正常胃肠蠕动所必需的。产生正常起搏的机制尚不完全清楚。正常的胃肠收缩力和电慢波活动取决于细胞外 HCO ₃ ^-的存在。先前的转录分析确定了编码生电 Na ⁺ /HCO ₃ ^-的 mRNA 的富集小鼠小肠起搏器肌层 ICC 中的协同转运蛋白 (NBCe1) 基因 (Slc4a4)。我们旨在确定 NBCe1 蛋白在小鼠胃肠道 ICC 中的分布，并鉴定小鼠和人小肠肌膜中 Slc4a4 基因的转录本。我们通过小鼠和人体组织中的免疫荧光标记确定了 NBCe1 免疫反应性 (NBCe1-IR) 的分布。在小鼠中，NBCe1-IR 仅限于 Kit 阳性的胃和小肠肌间 ICC 以及大肠的亚肌肉 ICC；那是ICC的慢波生成子集。ICC 的其他亚型为 NBCe1 阴性。定量实时 PCR 鉴定了 >500 倍的 Slc4a4-207 和 Slc4a4-208 转录本（IP3 释放的 IP3 受体结合蛋白）^creERT2/+、Rpl22 ^tm1.1Psam/Sj小鼠和来自 Kit ^tm1Rosay小鼠的单个 GFP 阳性 ICC 。人空肠肌层 ICC 也是 NBCe1 阳性，SLC4A4-201 和 SLC4A4-204 RNA 相对于 SLC4A4-202 富集 > 300 倍。总之，在具有电起搏器功能的 ICC 中表达的 NBCe1 蛋白由 Slc4a4 基因转录本编码，该转录本产生 NBCe1 的 IRBIT 调节同种型。总之，Na ⁺ /HCO ₃ ^-通过 NBCe1 的协同转运有助于在 ICC 子集中产生起搏器活动。