Phosphodiesterase Type-1 Regulates Transient BK Currents and Contractility of Human Urinary Bladder Smooth Muscle

Abstract

Large conductance Ca2+-activated K+ (BK) channels are critical regulators of urinary bladder smooth muscle (UBSM) function. We aimed to investigate phosphodiesterase type 1 (PDE1) interactions with BK channels in human UBSM to determine the mechanism by which PDE1 regulates human urinary bladder function. A combined electrophysiological, functional, and pharmacological approach was applied using human UBSM specimens obtained from open bladder surgeries. The perforated whole cell patch-clamp technique was used to record transient BK currents (TBKCs) and the cell membrane potential in freshly-isolated human UBSM cells in combination with the selective PDE1 inhibitor, 8-methoxymethyl-3-isobutyl-1-methylxanthine (8MM-IBMX). Isometric tension recordings were used to measure spontaneous phasic and electrical field stimulation (EFS)-induced contractions in human UBSM isolated strips. Selective pharmacological inhibition of PDE1 with 8MM-IBMX (10 μM) increased TBKC activity in human UBSM cells, which was abolished by subsequent inhibition of protein kinase A (PKA) with H-89 (10 μM). The stimulatory effect of 8MM-IBMX on TBKCs was reversed upon activation of muscarinic acetylcholine receptors with carbachol (1 μM). 8MM-IBMX (10 μM) hyperpolarized the UBSM cell membrane potential, an effect blocked by PKA inhibition. 8MM-IBMX significantly decreased spontaneous phasic and nerve-evoked contractions of human UBSM isolated strips.The results reveal that pharmacological inhibition of PDE1 attenuates human UBSM excitability and contractility by activating BK channels via a PKA-dependent mechanism. The data also suggest interactions between PDE1 and muscarinic signaling pathways in human UBSM. Overall, our data provide mechanistic evidence that pharmacological inhibition of PDE1 can be a useful therapeutic approach for the treatment of overactive bladder syndrome by attenuating UBSM excitability and contractility. These investigations are an important step in validating PDE1 as a potential novel therapeutic target for overactive bladder.Supported by NIH R01DK106964 and R01DK084284 to Georgi V. Petkov.