Origin of Detrusor Smooth Muscle Excitability - Summary The function of the urinary bladder – to store and release urine – seems deceptively simple. Yet, these roles require the coordination of sensory, cognitive, and motor systems so that urine is neither voided too frequently nor retained too long. Despite being a fundamental bodily function, the underlying physiological mechanisms that allow the bladder to properly store and release urine remain elusive. Disruptions in normal bladder physiology can lead to incontinence or, in extreme cases, remodeling that renders the bladder wall nonfunctional. The bladder wall is comprised predominantly of the detrusor smooth muscle (DSM), and it is the contraction and relaxation of DSM that mediates the voiding and storage functions of the bladder. DSM is an excitable tissue, exhibiting action potentials that cause transient contractions. In the intact bladder, DSM transient contractions cause localized deformations in the wall of the bladder, or micromotions. These micromotions can be coordinated and propagated in waves to produce transient pressure events, that trigger bursts of afferent nerve activity and signal bladder fullness to the central nervous system. Yet the drivers of these contractions remain unknown. The rhythmic nature of these micromotions suggests some form of pacemaker activity. Calcium-activated chloride channels (CaCl) are known to contribute to pacemaker activity in other tissues and are present in DSM. This proposal addresses the pathways involved in DSM excitability and how phasic contractions are synchronized between adjacent cells. I hypothesize that prostaglandins released during bladder filling stimulate downstream CaCl to initiate DSM depolarization. In Aim 1.1, I will establish a connection between intracellular- Ca2+ elevating Gq protein-coupled prostaglandin receptors in the bladder wall and CaCl that induces DSM excitability. I will then explore the spatial and temporal spread of action potentials that lead to transient pressure events. I will combine imaging techniques with an ex-vivo pressurized bladder to simultaneously record the spread of Ca2+ signals relative to transient pressure events before and after disrupting rhythmic contractions. The physiological effect of CaCl on bladder function will be examined in Aim 1.2. I will use a smooth muscle- specific knockout mouse model to explore the effect of CaCl loss on conscious voiding behavior in vivo. Completing this project provides insights into how DSM excitation is generated and spreads to produce transient pressure events. By determining whether pacing cells play a role in this process, we will be better suited to study and treat bladder dysfunctions. In Aim 2 of the K00 phase, I propose to study the microvasculature of the bladder, which experiences mechanical forces during filling that significantly reduce blood flow. Despite prolonged hypoxia, ischemia/reperfusion injury of the bladder does not occur. I will use functional ultrasound, fluorescent microscopy, and myography of isolated vessels to evaluate how bladder microvasculature regulates blood flow so perfusion remains sufficient and voiding contractions occur. These results could inform treatment decisions for ischemic bladder disorders and other organ systems that are vulnerable to ischemia/reperfusion injury.
