Large conductance Ca2+-activated K+ channel activation with NS1619 decreases myogenic and neurogenic contractions of rat detrusor smooth muscle

Abstract

Large conductance voltage- and Ca2+-activated K+ channels are important in regulating detrusor smooth muscle (DSM) function. Here, we examined systematically how the BK channel pharmacological activation modulates DSM contractility. NS1619, a potent BK channel activator, was utilized as a pharmacological tool to investigate the effect of BK channel activation on rat DSM contractility. Isometric tension recordings of DSM strips isolated from rat urinary bladder were performed systematically under various experimental conditions. NS1619 (30 μM) substantially diminished DSM spontaneous contraction amplitude, muscle force integral, frequency, duration and muscle tone. This effect was blocked by iberiotoxin, a BK channel selective inhibitor. NS1619 inhibited the phasic and tonic contractions in DSM strips pre-contracted with either the cholinergic agonist, carbachol (0.1 μM), or the depolarizing agent, KCl (20 mM and 60 mM KCl). In the presence of elevated KCl, the inhibitory effect of NS1619 was significantly reduced, indicating that BK channel activation is the underlying mechanism of NS1619 action. BK channel activation with NS1619 dramatically decreased the amplitude of electrical field stimulation (EFS)-induced contractions under a range of stimulation frequencies (0.5–50 Hz). In the presence of specific neurotransmitter inhibitors, BK channel activation with NS1619 significantly decreased both cholinergic and purinergic components of EFS-induced contractions. We conclude that BK channel activation with NS1619 significantly inhibited spontaneous, pharmacologically induced and nerve-evoked DSM contractions. Targeting the BK channel with selective openers may offer a unique opportunity to control DSM contractile activity, including pathophysiological conditions such as overactive bladder and detrusor overactivity, regardless of the underlying cause.

Suppression of human detrusor smooth muscle excitability and contractility via pharmacological activation of large conductance Ca2+-activated K+ channels

“…This decrease of intracellular Ca 2ϩ is caused by activation of the BK channel, membrane hyperpolarization, and subsequent inhibition of the L-type voltage-gated Ca 2ϩ channels. These findings are also supported by earlier studies showing that NS-1619 decreases rat and guinea pig DSM contractility by activation of the BK channel and inhibition of L-type voltage-gated Ca 2ϩ channels (36,38).…”

“…NS-1619 (EC 50 ϭ 10 -30 M) decreases contractility in guinea pig DSM by activation of the BK channel (36). Our recent study revealed that BK channel activation with NS-1619 significantly inhibits spontaneous, pharmacologically induced and nerve-evoked contractions in rat DSM (38). However, functional studies performed on human DSM specimens have not addressed the role of BK channel pharmacological activation under normal physiological conditions of spontaneous activity but rather after DSM depolarization with KCl (31).…”

“…Development of drugs that can enhance BK channel activity have been proposed and investigated particularly as a treatment option for urinary bladder dysfunction (3,4,17,37). Earlier studies have demonstrated that BK channel activation decreases DSM excitability and contractility in various experimental animal models (23,37,38). Studies involving genetic alterations in BK channel expression suggest that increasing BK channel activity may provide substantial therapeutic benefit in the treatment of DO (7,26,27).…”

“…Antimuscarinic drugs, which are currently the primary pharmacologic therapy for OAB, have adverse side effects and limited effectiveness (1). Since BK channels have been identified to play a prominent role in the regulation of DSM excitability and contractility, they may be a valid pharmacological target for the treatment of bladder disorders such as OAB (5,15,20,23,31,34,35,38). Development of drugs that can enhance BK channel activity have been proposed and investigated particularly as a treatment option for urinary bladder dysfunction (3,4,17,37).…”

Ca2+‐activated K+ channel (KCa) stimulation improves relaxant capacity of PDE5 inhibitors in human penile arteries and recovers the reduced efficacy of PDE5 inhibition in diabetic erectile dysfunction

“…In ion efflux in vitro assays, EC50 for BK has reported to be in 1-4 mM range for NS1619 and NS-8 (Parihar et al, 2003b). Most data reporting the specificity of these molecules have been generated in functional studies where a dependency on BK activation in the NS-8-or NS1619-induced effects is abolished by BK-selective toxins (Holland et al, 1996;Malysz et al, 2004;Soder and Petkov, 2011). Although NS-8 is a known activator of BK (Parihar et al, 2003b;Malysz et al, 2004), NS1619 is considered to be the only selective BK opener by some authors (Ghatta et al, 2006) without any effect on KATP, voltage-gated K + , Na + or Ca 2+ channels (Olesen et al, 1994).…”