Date of Award
Open Access Dissertation
College of Pharmacy
Georgi V Petkov
Overactive bladder (OAB) is a pathophysiological condition which is characterized by the urinary bladder's failure to achieve proper storage of urine. OAB has a tremendous impact on the patient's quality of life by disturbing his sleep, work, and sexual activity. About 17% of Americans are affected with this disease and most patients experience symptoms of urgency, frequent urination, and abnormally elevated detrusor smooth muscle (DSM) contractility. Despite, numerous attempts to treat the disorder in the past with antimuscarinics and now with beta3 adrenergic receptors (beta3-AR agonists), OAB still remains a serious public health issue because the long term efficacy of these drugs remains questionable. Therefore, it is critical to explore new avenues and design new strategies in order to help improve the quality of life of more than 33 million people. K+ channels and beta3-AR have been shown to be key regulators of smooth muscle excitability and contractility in various species; however, information about their expression and functional role in the DSM of humans was limited. In our study, we first investigated the molecular expression of several K+ channels in human DSM cells using RT-PCR, qPCR, western blot, and immunostaining techniques, then tested their ability to affect DSM contractility by using isometric DSM tension recordings and selective pharmacological modulators. We found that two Ca2+-activated K+ channels including BK and SK3 channels as well as several voltage-gated K+ channels including Kv2.1, Kv2.2, Kv7.4, and Kv7.5 channels were expressed in human DSM cells. We also found that pharmacological inhibition of BK or SK3 channels with iberiotoxin, a BK channel blocker or apamin, a SK channel blocker, respectively, significantly increased human DSM spontaneous and nerve-evoked contractions in vitro. Similarly, pharmacological inhibition of Kv2 channels with stromatoxin-1, a Kv2 channel antagonist or Kv7 channels with XE991, a Kv7 channel antagonist, also increased human DSM spontaneous phasic and nerve-evoked contractions in vitro. On the other hand, application of retigabine, a Kv7 channel activator induced relaxation of human DSM strips spontaneous phasic and nerve-evoked contractions. As for the role of beta3-AR in human DSM, we found that pharmacological activation of beta3-AR with BRL37344, a beta3-AR agonist causes relaxation of human DSM nerve-evoked contractions in vitro. We further demonstrated that the beta3-AR mediated relaxation observed during nerve-evoked contractions was facilitated by BK channel activity. Finally, we obtained direct evidence suggesting that the decrease in BK channels expression and function is associated with symptoms of neurogenic detrusor overactivity.
In conclusion our study suggest that pharmacological modulation of K+ channels (BK, SK3, Kv2, and Kv7 channels) or beta3-AR affect DSM contractility, therefore making K+ channels and beta3-AR likely drug targets for the treatment of OAB.
Afeli, S. A.(2013). K+ Channels and Beta3 Adrenergic Receptors as New Pharmacological Targets for Overactive Bladder Treatment. (Doctoral dissertation). Retrieved from http://scholarcommons.sc.edu/etd/1706