期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2020
卷号：117
期号：48
页码：30775-30786
DOI：10.1073/pnas.2016959117
出版社：The National Academy of Sciences of the United States of America
摘要：TRPML1 (transient receptor potential mucolipin 1) is a Ca 2 -permeable, nonselective cation channel that is predominantly localized to the membranes of late endosomes and lysosomes (LELs). Intracellular release of Ca 2 through TRPML1 is thought to be pivotal for maintenance of intravesicular acidic pH as well as the maturation, fusion, and trafficking of LELs. Interestingly, genetic ablation of TRPML1 in mice ( Mcoln1 −/− ) induces a hyperdistended/hypertrophic bladder phenotype. Here, we investigated this phenomenon further by exploring an unconventional role for TRPML1 channels in the regulation of Ca 2 -signaling activity and contractility in bladder and urethral smooth muscle cells (SMCs). Four-dimensional (4D) lattice light-sheet live-cell imaging showed that the majority of LELs in freshly isolated bladder SMCs were essentially immobile. Superresolution microscopy revealed distinct nanoscale colocalization of LEL-expressing TRPML1 channels with ryanodine type 2 receptors (RyR2) in bladder SMCs. Spontaneous intracellular release of Ca 2 from the sarcoplasmic reticulum (SR) through RyR2 generates localized elevations of Ca 2 (“Ca 2 sparks”) that activate plasmalemmal large-conductance Ca 2 -activated K (BK) channels, a critical negative feedback mechanism that regulates smooth muscle contractility. This mechanism was impaired in Mcoln1 −/− mice, which showed diminished spontaneous Ca 2 sparks and BK channel activity in bladder and urethra SMCs. Additionally, ex vivo contractility experiments showed that loss of Ca 2 spark–BK channel signaling in Mcoln1 −/− mice rendered both bladder and urethra smooth muscle hypercontractile. Voiding activity analyses revealed bladder overactivity in Mcoln1 −/− mice. We conclude that TRPML1 is critically important for Ca 2 spark signaling, and thus regulation of contractility and function, in lower urinary tract SMCs.
