| COX-2 Co-localizes with Vimentin and c-Kit in Bladder Interstitial Cells and Causes Detrusor Smooth Muscle Spontaneous Tone by Generating PGE2 |
AUTHORS: Clinton W Collins MD, Adam P Klausner MD, Amy Miner MD, Benjamin W Herrick MD, Harry P Koo MD, Paul H Ratz MD; Division of Urology, VCU Medical Center, Richmond, VA
ABSTRACT:
Introduction and Objective: Destrusor smooth muscle (DSM) isolated from patients with overactive bladder (OAB) displays enhanced spontaneous rhythmic tone (SRT) that is abolished by inhibitors of c-Kit, a receptor tyrosine kinase. These data fit a model in which OAB is caused, in part, by enhancement of an intrinsic bladder wall contraction oscillator. The intrinsic oscillator responsible for gut pacemaker activity is the c-Kit-dependent Interstitial Cell of Cajal. Because of its high degree of SRT, isolated strips of rabbit bladder represent a model of human OAB. We tested the hypothesis that rabbit bladder interstitial cells (BIC) play the key role in SRT by generating prostaglandins that cause DSM rhythmic contractions.
METHODS:
Longitudinal strips of DSM free of serosa and mucosa were isolated from adult laboratory rabbits, incubated in aerated physiological salt solution and suspended by tissue clips between a micrometer (for length adjustments) and a force transducer (to measure isometric contraction). Some tissues were frozen and prepared for immunohistochemistry (IHC) and confocal image analysis.
RESULTS:
Two structurally dissimilar selective COX-2 inhibitors, NS-398 & LM-1685, and a selective EP1 receptor inhibitor, SC-51322, abolished SRT. A selective prostaglandin FP receptor inhibitor, ICI 192,605, had no effect. COX-2 immunofluorescence labeling (red - Image 1) co-localized with the ICC markers, c-kit (green - Image 2) and vimentin (not shown) in BIC (arrow) but not DSM (purple = phalloidin DSM stain; blue = DAPI nuclear stain).
CONCLUSIONS:
These data indicate that COX-2 is basally active in rabbit BIC and support a model in which BIC acts as an intrinsic oscillator by generating a paracrine agent, PGE2, that stimulates DSM contraction, causing SRT. Because human DSM SRT is elevated in patients with OAB, these data implicate two novel targets, COX-2 & EP1 receptors, for the treatment of this chronic disorder.
