BK Channel-Mediated Relaxation of Urinary Bladder Smooth Muscle: A Novel Paradigm for Phosphodiesterase Type 4 Regulation of Bladder Function

• Published in: The Journal of pharmacology and experimental therapeutics 2014-04, Vol.349 (1), p.56-65
• Main Authors: Xin, Wenkuan, Li, Ning, Cheng, Qiuping, Petkov, Georgi V.
• Format: Article
• Language: English
• Subjects: 4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone - administration & dosage; 4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone - pharmacology; Animals; Calcium - metabolism; Calcium Signaling - drug effects; Cell Polarity - drug effects; Cells, Cultured; Cyclic AMP-Dependent Protein Kinases - antagonists & inhibitors; Cyclic Nucleotide Phosphodiesterases, Type 4 - metabolism; Electric Stimulation; Gastrointestinal, Hepatic, Pulmonary, and Renal; Guinea Pigs; Large-Conductance Calcium-Activated Potassium Channels - metabolism; Male; Membrane Potentials - drug effects; Muscle Relaxation - drug effects; Muscle Relaxation - physiology; Muscle, Smooth - cytology; Muscle, Smooth - drug effects; Muscle, Smooth - physiology; Phosphodiesterase 4 Inhibitors - administration & dosage; Phosphodiesterase 4 Inhibitors - pharmacology; Rolipram - administration & dosage; Rolipram - pharmacology; Urinary Bladder - cytology; Urinary Bladder - drug effects; Urinary Bladder - physiology
• ISSN: 0022-3565; 1521-0103
• DOI: 10.1124/jpet.113.210708

Elevation of intracellular cAMP and activation of protein kinase A (PKA) lead to activation of large conductance voltage- and Ca2+-activated K+ (BK) channels, thus attenuation of detrusor smooth muscle (DSM) contractility. In this study, we investigated the mechanism by which pharmacological inhibition of cAMP-specific phosphodiesterase 4 (PDE4) with rolipram or Ro-20-1724 (C15H22N2O3) suppresses guinea pig DSM excitability and contractility. We used high-speed line-scanning confocal microscopy, ratiometric fluorescence Ca2+ imaging, and perforated whole-cell patch-clamp techniques on freshly isolated DSM cells, along with isometric tension recordings of DSM isolated strips. Rolipram caused an increase in the frequency of Ca2+ sparks and the spontaneous transient BK currents (TBKCs), hyperpolarized the cell membrane potential (MP), and decreased the intracellular Ca2+ levels. Blocking BK channels with paxilline reversed the hyperpolarizing effect of rolipram and depolarized the MP back to the control levels. In the presence of H-89 [N-[2-[[3-(4-bromophenyl)-2-propenyl]amino]ethyl]-5-isoquinolinesulfonamide dihydrochloride], a PKA inhibitor, rolipram did not cause MP hyperpolarization. Rolipram or Ro-20-1724 reduced DSM spontaneous and carbachol-induced phasic contraction amplitude, muscle force, duration, and frequency, and electrical field stimulation-induced contraction amplitude, muscle force, and tone. Paxilline recovered DSM contractility, which was suppressed by pretreatment with PDE4 inhibitors. Rolipram had reduced inhibitory effects on DSM contractility in DSM strips pretreated with paxilline. This study revealed a novel cellular mechanism whereby pharmacological inhibition of PDE4 leads to suppression of guinea pig DSM contractility by increasing the frequency of Ca2+ sparks and the functionally coupled TBKCs, consequently hyperpolarizing DSM cell MP. Collectively, this decreases the global intracellular Ca2+ levels and DSM contractility in a BK channel-dependent manner.