Benzbromarone inhibition of phasic smooth muscle contractions of mouse urinary bladder
Authors: Beaulieu Elleanor , Heppner Thomas , Hennig Grant , Nelson Mark , Herrera Gerald 
Published: May 2023

Calcium-activated chloride (ClCa) channels play a key role in generating pacemaker currents responsible for maintaining motility in the phasic smooth muscle of the gastrointestinal tract. These channels may play a similar role in the urinary bladder, resulting in the bladder exhibiting spontaneous phasic contractions. These phasic contractions are known to underlie non-voiding contractions and transient pressure events. The purpose of this study was to determine whether the putative ClCa channel inhibitor benzbromarone has an inhibitory effect on transient pressure events in the isolated perfused mouse urinary bladder. We hypothesized benzbromarone would abolish bladder transient pressure events. Urinary bladders were isolated from male C57Bl6/J mice (7-8 wks old, 23.2-24.5 g body weight) post-euthanasia. Isolated bladders were placed in ice-cold nominally Ca-free dissection solution. Ureters were tied off, the bladder was cannulated through the urethra, and submerged in an organ bath containing physiological saline solution (37 °C, pH 7.4). The bladder was then attached to a syringe pump and inline pressure transducer to infuse at a constant rate of 1.8 mL/hr while recording intraluminal pressure. Urinary bladders were filled until they reached an intravesical pressure of 25 mmHg, which was defined as bladder capacity. Upon reaching bladder capacity, the bladder was emptied through the urethral cannula. Three fills were performed under baseline conditions to establish a consistent pressure-volume relationship. Benzbromarone (10 μM) was applied for 20 minutes. Bladders were subsequently filled to 80 % capacity and transient pressure events allowed to stabilize for at least 5 minutes. Transient pressure events were recorded in the absence and presence of benzbromarone. Transient pressure event frequency, amplitude, and duration were analyzed using a custom MatLab algorithm. Under baseline conditions, transient pressure events occurred at a frequency of 5.2 ± 0.8 events per minute (n = 3). Inhibition of ClCa with benzbromarone decreased transient pressure event frequency to 2.1±1.1 events per minute (n = 3, p = 0.08, paired t-test). Similarly, benzbromarone decreased transient pressure event amplitude from a baseline value of 0.22 ± 0.02 mmHg (n = 3) to 0.06 ± 0.04 mmHg (n = 3, p = 0.17, paired t-test). Transient pressure event duration was unaffected by benzbromarone (baseline duration 5.3 ± 0.3 sec, benzbromarone duration 5.2 ± 2.7 sec, n = 3, p= 0.98, paired t-test). In summary, we found that the putativeClCa channel inhibitor benzbromarone disrupted the rhythmicity and amplitude of transient pressure events, while leaving the duration of these contractile events unaltered. This suggests that ClCa channels play a role in generating the rhythm of phasic smooth muscle contractions in the bladder. The cellualr and molecular basis underlying the involvement of ClCa channels in the urinary bladder remains to be explored. This work was supported by a grant from the National Institute of Diabetes and Digestive and Kidney Diseases (R01DK125543). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.