Department of Biochemistry, University of Texas Health Science Center at Tyler, USA.
Am J Respir Cell Mol Biol. 2011 Nov;45(5):1007-14. doi: 10.1165/rcmb.2011-0004OC. Epub 2011 May 11.
Salt absorption via alveolar epithelial Na(+) channels (ENaC) is a critical step for maintaining an airspace free of flooding. Previously, we found that 8-(4-chlorophenylthio)-guanosine-3',5'-cyclic monophosphate-Na (CPT-cGMP) activated native and heterologous ENaC. To investigate the potential pharmacological relevance, we applied this compound intratracheally to human lungs and found that ex vivo alveolar fluid clearance was increased significantly. Furthermore, this compound eliminated self-inhibition in human lung H441 cells and in oocytes expressing human αβγ but not δβγ channels. To further elucidate this novel mechanism, we constructed mutants abolishing (β(ΔV348) and γ(H233R)) or augmenting (α(Y458A) and γ(M432G)) self-inhibition. The mutants eliminating self-inhibition lost their responses to CPT-cGMP, whereas those enhancing self-inhibition facilitated the stimulatory effects of this compound. CPT-cGMP was unable to activate a high P(o) mutant (β(S520C)) and plasmin proteolytically cleaved channels. Our data suggest that elimination of self-inhibition of αβγ ENaC may be a novel mechanism for CPT-cGMP to stimulate salt reabsorption in human lungs.
肺泡上皮钠离子通道（ENaC）通过吸收盐分来维持肺泡腔免受积水影响，这是一个关键步骤。此前，我们发现 8-（4-氯苯硫基）-鸟苷-3'，5'-环单磷酸钠盐（CPT-cGMP）可以激活天然和异源 ENaC。为了研究其潜在的药理学相关性，我们将该化合物通过气管内给药的方式应用于人类肺部，并发现肺泡液清除率显著增加。此外，该化合物消除了人肺 H441 细胞和表达人αβγ但不表达 δβγ通道的卵母细胞中的自我抑制。为了进一步阐明这种新的机制，我们构建了消除（β（ΔV348）和γ（H233R））或增强（α（Y458A）和γ（M432G））自我抑制的突变体。消除自我抑制的突变体失去了对 CPT-cGMP 的反应，而增强自我抑制的突变体促进了该化合物的刺激作用。CPT-cGMP 无法激活具有高 P(o)的突变体（β（S520C））和纤溶酶蛋白水解切割的通道。我们的数据表明，消除αβγ ENaC 的自我抑制可能是 CPT-cGMP 刺激人类肺部盐重吸收的一种新机制。
