Sarcolemmal localisation of Na+/H+ exchange and Na+HCO3- co-transport influences the spatial regulation of intracellular pH in rat ventricular myocytes
Sarcolemmal localisation of Na+/H+ exchange and Na+HCO3- co-transport influences the spatial regulation of intracellular pH in rat ventricular myocytes
复制标题
DOI：
10.1113/jphysiol.2012.249664
复制
发表时间：
2013-05-01
影响因子：
5.5
通讯作者：
Vaughan-Jones, Richard D.
中科院分区：
文献类型：
--
作者：
Garciarena, Carolina D.;Ma, Yu-ling;Vaughan-Jones, Richard D.
通过Na+/H+交换（NHE 1）和Na+ HCO 3共转运（NBC）的膜酸挤出对于维持低细胞质[H+]（类似于60 nm，相当于细胞内pH（pHi）为7.2）至关重要。这可以保护心肌功能免受H+离子的高化学反应性的影响，H+离子是代谢的普遍终产物。我们在这里显示，在大鼠心室肌细胞，荧光抗体映射的NBC亚型NBCe 1和NBCn 1侧肌膜，闰盘和横小管（t-小管），而NHE 1是不存在的t-小管。这种意想不到的差异匹配pHi调节的功能测量（使用AM负载的SNARF-1，pH荧光团）。因此，肌细胞去紧张（通过短暂暴露于1.5 M甲酰胺）减少了40%的NBC的整体酸挤出，而不影响NHE 1。类似地，共聚焦pHi成像揭示NBC刺激诱导从酸中毒的空间上均匀的pHi恢复，而NHE 1刺激诱导恢复期间的pHi不均匀性（类似于0.1单位，持续2-3分钟），特别是在闰盘通常位于的细胞末端，并且其中NHE 1免疫染色突出。数学建模表明，这种诱导的本地pHi微区有利于低细胞质H+流动性和长H+扩散距离，特别是表面NHE 1转运介导高膜通量。我们的研究结果为心室肌细胞中[H+]（1）调节的空间定位提供了第一个证据，表明通过保护pHi，NHE 1优先保护闰盘处的间隙连接通讯，而NBC局部保护t-管兴奋-收缩偶联。
Membrane acid extrusion by Na+/H+ exchange (NHE1) and Na+HCO3 co-transport (NBC) is essential for maintaining a low cytoplasmic [H+] (similar to 60 nm, equivalent to an intracellular pH (pHi) of 7.2). This protects myocardial function from the high chemical reactivity of H+ ions, universal end-products of metabolism. We show here that, in rat ventricular myocytes, fluorescent antibodies map the NBC isoforms NBCe1 and NBCn1 to lateral sarcolemma, intercalated discs and transverse tubules (t-tubules), while NHE1 is absent from t-tubules. This unexpected difference matches functional measurements of pHi regulation (using AM-loaded SNARF-1, a pH fluorophore). Thus, myocyte detubulation (by transient exposure to 1.5 m formamide) reduces global acid extrusion on NBC by 40%, without affecting NHE1. Similarly, confocal pHi imaging reveals that NBC stimulation induces spatially uniform pHi recovery from acidosis, whereas NHE1 stimulation induces pHi non-uniformity during recovery (of similar to 0.1 units, for 2-3 min), particularly at the ends of the cell where intercalated discs are commonly located, and where NHE1 immunostaining is prominent. Mathematical modelling shows that this induction of local pHi microdomains is favoured by low cytoplasmic H+ mobility and long H+ diffusion distances, particularly to surface NHE1 transporters mediating high membrane flux. Our results provide the first evidence for a spatial localisation of [H+](1) regulation in ventricular myocytes, suggesting that, by guarding pHi, NHE1 preferentially protects gap junctional communication at intercalated discs, while NBC locally protects t-tubular excitation-contraction coupling.