Wednesday, April 2, 2025
4/2/2025
Cav1.2 in bladder physiology and pathology - Abstract: The L-type voltage-gated calcium channel Cav1.2 is responsible for the excitation-contraction coupling of bladder smooth muscle (BSM), making it an attractive drug target for the treatment of lower urinary tract symptoms (LUTS). Nifedipine, a Cav1.2 antagonist, inhibits BSM contraction. However, trials of nifedipine and other calcium channel blockers (CCBs) for LUTS patients were unsuccessful. On the contrary, cardiologists and epidemiologists have consistently reported that intake of CCBs like nifedipine causes higher voiding frequency and worsen the severity of LUTS in patients. The mechanism of this mystery has never been answered, which hampers its application as a useful drug target for LUTS treatment. We have discovered that ketamine functions as a Cav1.2 antagonist to cause ketamine cystitis - a painful bladder syndrome presenting as frequency, small voids, and incontinence. We have discovered that intravesical infusion of nifedipine or ketamine directly induces voiding frequency in mice. Conversely, Cav1.2 agonist induces fewer but larger voids, suggesting Cav1.2 agonists as potential novel therapeutics for LUTS. In addition to BSM, we have further discovered the presence of Cav1.2 in urothelium, and urothelial specific deletion of Cav1.2 (UCav1.2-/-) in mice results in dramatic voiding frequency, small bladder capacity, and diminished voiding efficiency, a phenotype closely resembles that produced by intravesical infusion of nifedipine in mice, and the symptoms of patients with ketamine cystitis or CCB users, indicating a crucial role of Cav1.2 in urothelial function and bladder pathology. We propose that disruption of Cav1.2 signaling causes deficient urothelial exocytosis and reduced bladder capacity, which leads to abnormal mechanosensation by elevated ATP signaling and result in voiding frequency. We will test our hypothesis by the following two aims: Aim 1. We will define bladder storage abnormality in UCav1.2-/- mice by studying Cav1.2 regulated umbrella cell (UC) exocytosis. We will use videocystometry and electrophysiology to determine UC exocytosis and bladder urodynamics, and test its Cav1.2- and AC-cAMP-PKA- dependence. We will further manipulate Cav1.2 expression by gene silence or knockin specifically in UCs, to determine whether it can rescue the voiding abnormalities observed in UCav1.2- /- mice or induces a phenotype resembling UCav1.2-/- in wild type mice. Aim 2. We will define urothelial mechanosensory/voiding abnormality in UCav1.2-/- mice. We will test whether mechanosensation is altered in UCav1.2-/- mice by abnormal urothelial ATP signaling. We will further test whether elevated urothelial ATP signaling by ablation of ATP hydrolase Entpd3 in urothelium leads to voiding frequency as proposed in UCav1.2-/- mice. In brief, our data indicate a crucial role of Cav1.2 in regulating bladder storage and voiding function, supporting a novel mechanism on urothelial Cav1.2-mediated exocytosis and ATP signaling. A complete understanding of this mechanism should answer the longstanding question of why Cav1.2 antagonists are of no benefit for LUTS patients, and potentially leads to novel therapeutics for LUTS treatment.
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