About 17% of the US population suffers from overactive bladder (OAB) and the associated economic cost is more than $26 billion per year. OAB is a poorly understood disorder characterized by increased urinary bladder smooth muscle (UBSM) contractility. In experimental animals, the large-conductance voltage-gated and Ca2+- activated K+ (BK) channel is a key regulator of UBSM membrane excitability and contractility. In general, inhibition of these ion channels leads to increased membrane excitability and contractility, whereas their activation hyperpolarizes the membrane and decreases contractility. However, the BK channel function and regulation in human UBSM is unknown. Our basic science research group, in collaboration with clinical scientists, is in a unique position to regularly utilize human UBSM tissues from donor patients to study BK channel function in humans and correlate the basic science findings with the clinical and urodynamic profile of the patients. Our long-term goal is to understand the mechanisms that regulate human UBSM BK channels under normal physiological conditions and to develop novel therapeutic strategies to control OAB. The objective of this application is to elucidate the physiological role and regulatory mechanisms of the BK channel in human UBSM contractility under normal physiological conditions. We will test the novel hypothesis that the BK channel determines the myogenic activity of human UBSM and it is regulated by cholinergic, 2- adrenergic, and differential Ca2+ signals with the following Aims:
Aim 1. Elucidate the role of Ca2+ in the regulation of the BK channel in human UBSM myogenic activity;
Aim 2. Elucidate the functional link between 2-adrenoceptors (2-ARs) and BK channels in UBSM;
and Aim 3. Elucidate the functional link between muscarinic (M2 and M3) receptors and BK channels in UBSM. We will employ a combined approach, using state-of-the-art techniques, to determine the role of BK channels and their regulatory mechanisms in UBSM function from single molecules and isolated cells to intact tissue and the whole organism. Our team has the advantage of using full-thickness human UBSM tissues from open surgeries, which allows us to conduct advanced patch-clamp electrophysiology, functional studies on human UBSM contractility, and molecular biology experiments simultaneously. Thus, we can identify channel regulatory proteins, and then correlate BK channel activity with human UBSM contractility properties. Our research team's basic science and clinical expertise may lead to important translational observations. The proposed studies are expected to provide novel insights on BK channel function and regulation by cholinergic, 2-adrenergic, and Ca2+ signals in human UBSM. The results will have a significant impact on urological research with a strong potential to provide novel therapeutic approaches to help a large population of patients suffering from OAB.

Public Health Relevance

Urinary bladder dysfunction is a major health issue in the US. Overactive bladder and related urinary incontinence are poorly understood disorders and effective therapeutic agents to control these conditions are lacking. Our basic science research group in collaboration with clinical scientists uses state-of-the-art techniques at the molecular, cellular, and tissue levels, to determine the role of cell membrane potassium ion channels as novel therapeutic targets to control urinary bladder dysfunction.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Urologic and Kidney Development and Genitourinary Diseases Study Section (UKGD)
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Mullins, Christopher V
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University of South Carolina at Columbia
Schools of Pharmacy
United States
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Parajuli, Shankar P; Hristov, Kiril L; Cheng, Qiuping et al. (2015) Functional link between muscarinic receptors and large-conductance Ca2+ -activated K+ channels in freshly isolated human detrusor smooth muscle cells. Pflugers Arch 467:665-75
Xin, Wenkuan; Li, Ning; Cheng, Qiuping et al. (2014) BK channel-mediated relaxation of urinary bladder smooth muscle: a novel paradigm for phosphodiesterase type 4 regulation of bladder function. J Pharmacol Exp Ther 349:56-65
Petkov, Georgi V (2014) Central role of the BK channel in urinary bladder smooth muscle physiology and pathophysiology. Am J Physiol Regul Integr Comp Physiol 307:R571-84
Hristov, Kiril L; Smith, Amy C; Parajuli, Shankar P et al. (2014) Large-conductance voltage- and Ca2+-activated K+ channel regulation by protein kinase C in guinea pig urinary bladder smooth muscle. Am J Physiol Cell Physiol 306:C460-70
Parajuli, Shankar P; Provence, Aaron; Petkov, Georgi V (2014) Prostaglandin E2 excitatory effects on guinea pig urinary bladder smooth muscle: a novel regulatory mechanism mediated by large-conductance voltage- and Ca2+-activated K+ channels. Eur J Pharmacol 738:179-85
Malysz, John; Afeli, Serge A Y; Provence, Aaron et al. (2014) Ethanol-mediated relaxation of guinea pig urinary bladder smooth muscle: involvement of BK and L-type Ca2+ channels. Am J Physiol Cell Physiol 306:C45-58
Hristov, Kiril L; Afeli, Serge A Y; Parajuli, Shankar P et al. (2013) Neurogenic detrusor overactivity is associated with decreased expression and function of the large conductance voltage- and Ca(2+)-activated K(+) channels. PLoS One 8:e68052
Afeli, Serge A Y; Rovner, Eric S; Petkov, Georgi V (2013) BRL37344, a *3-adrenergic receptor agonist, decreases nerve-evoked contractions in human detrusor smooth muscle isolated strips: role of BK channels. Urology 82:744.e1-7
Soder, Rupal P; Parajuli, Shankar P; Hristov, Kiril L et al. (2013) SK channel-selective opening by SKA-31 induces hyperpolarization and decreases contractility in human urinary bladder smooth muscle. Am J Physiol Regul Integr Comp Physiol 304:R155-63
Parajuli, Shankar P; Petkov, Georgi V (2013) Activation of muscarinic M3 receptors inhibits large-conductance voltage- and Ca2+-activated K+ channels in rat urinary bladder smooth muscle cells. Am J Physiol Cell Physiol 305:C207-14

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