TRPML1 (transient receptor potential mucolipin 1) is a Ca²⁺-permeable, nonselective cation channel that is predominantly localized to the membranes of late endosomes and lysosomes (LELs). Intracellular release of Ca²⁺ 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 Ca²⁺-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 Ca²⁺ from the sarcoplasmic reticulum (SR) through RyR2 generates localized elevations of Ca²⁺ (“Ca²⁺ sparks”) that activate plasmalemmal large-conductance Ca²⁺-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 Ca²⁺ sparks and BK channel activity in bladder and urethra SMCs. Additionally, ex vivo contractility experiments showed that loss of Ca²⁺ 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 Ca²⁺ spark signaling, and thus regulation of contractility and function, in lower urinary tract SMCs.

TRPML1（瞬时受体电位粘蛋白1）是可渗透Ca ^2+的非选择性阳离子通道，主要位于晚期内体和溶酶体（LELs）的膜上。人们认为通过TRPML1在细胞内释放Ca ²⁺对于维持囊内酸性pH以及LEL的成熟，融合和运输至关重要。有趣的是，小鼠中TRPML1的遗传消融（Mcoln1 ^-/-）诱导了膀胱过度扩张/肥大性表型。在这里，我们通过探索TRPML1通道在调节Ca ^2+中的非常规作用来进一步研究此现象。膀胱和尿道平滑肌细胞（SMCs）的信号传导活性和收缩性。二维（4D）格子光片活细胞成像显示，新鲜分离的膀胱SMC中的大多数LEL本质上是不动的。超分辨率显微镜显示膀胱SMCs中，表达LEL的TRPML1通道与2型ryanodine受体（RyR2）具有独特的纳米级共定位。Ca ²⁺通过RyR2从肌浆网（SR）自发地胞内释放会产生局部升高的Ca ²⁺（“ Ca ²⁺火花”），从而激活血浆中大电导Ca ²⁺活化的K ⁺（BK）通道，一种调节平滑肌收缩力的关键负反馈机制。此机制在Mcoln1 ^-/-小鼠中受损，其在膀胱和尿道SMC中表现出自发的Ca ²⁺火花减少和BK通道活性降低。此外，离体收缩实验表明，Mcoln1 ^-/-小鼠体内的Ca ²⁺ spark-BK通道信号丢失使膀胱和尿道平滑肌过度收缩。排空活性分析显示Mcoln1 ^-/-小鼠膀胱过度活动。我们得出结论，TRPML1对Ca ²⁺至关重要 在下尿路SMC中产生火花信号，从而调节收缩力和功能。