STRETCH DEPENDENT POTASSIUM CHANNEL REGULATION IN OVERACTIVE BLADDER

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Epidemiological studies have shown that urinary symptoms of overactive bladder become more common in postmenopausal women. The finding that estrogen treatment alleviates these symptoms highlights the association of overactive bladder with estrogen levels. Animal experiments confirm that estrogen deprivation causes uncoordinated function of the detrusor which can be reversed through estrogen treatment. Although there are many reports on the effects of estrogen on bladder function, no study concerning estrogen regulation of ion channel expression in bladder smooth muscle has been reported. The filling mechanism of bladder is myogenic, thus increased K+ channel activity in bladder myocytes during filing stabilizes membrane potential and relaxes the bladder smooth muscle. Furthermore, reduced K+ channel expression caused by low estrogen levels could explain postmenopausal overactive bladder. We have previously shown that stretch- dependent K+ (SDK) channels are expressed in bladder myocytes and contribute the myogenic mechanisms regulating bladder compliance during filling. As a molecular candidate, TREK-1 channels have properties (unitary conductance, pharmacological profile, and mechanosensitivity) identical to native SDK channels and are expressed in human and murine bladder myocytes. Therefore murine bladder should be considered an appropriate model to study the role of SDK channels in human bladder compliance. Estrogen receptors act via the regulation of transcriptional processes, thus leading to regulation of target gene expression. Therefore we will pursue the molecular mechanism of estrogen regulation on ion channels, in particular TREK-1 expression, in order to understand the phenomenon of overactive bladder in postmenopausal women. This investigation will test the hypothesis that TREK-1 channel expression in bladder is determined by an estrogen-regulated genomic influence and that impaired bladder function is a result of TREK-1 modulation of expression by estrogen. We will employ electrophysiology, molecular biology, and in vivo functional experiments to define the link between alterations in estrogen levels with TREK-1 channel expression, function and gene regulation in female bladder in control and ovariectomized murine models. The results of this proposal will highlight the importance of TREK-1 channels in stabilizing the membrane potential during bladder filling and will provide a novel specific target in the treatment of overactive bladder in postmenopausal females.