Functional BK channels facilitate the β3-adrenoceptor agonist-mediated relaxation of nerve-evoked contractions in rat urinary bladder smooth muscle isolated strips

We investigated the role of large-conductance Ca2+-activated K+ (BK) channels in β3-adrenoceptor (β3-AR)-induced relaxation in rat urinary bladder smooth muscle (UBSM). BRL 37344, a specific β3-AR agonist, inhibits spontaneous contractions of isolated UBSM strips. SR59230A, a specific β3-AR antagonist, and H89, a PKA inhibitor, reduced the inhibitory effect of BRL 37344. Iberiotoxin, a specific BK channel inhibitor, shifts the BRL 37344 concentration response curves for contraction amplitude, net muscle force, and tone to the right. Freshly dispersed UBSM cells and the perforated mode of the patch-clamp technique were used to determine further the role of β3-AR stimulation by BRL 37344 on BK channel activity. BRL 37344 increased spontaneous, transient, outward BK current (STOC) frequency by 46.0 ± 20.1%. In whole cell mode at a holding potential of Vh = 0 mV, the single BK channel amplitude was 5.17 ± 0.28 pA, whereas in the presence of BRL 37344, it was 5.55 ± 0.41 pA. The BK channel open probability was also unchanged. In the presence of ryanodine and nifedipine, the current-voltage relationship in response to depolarization steps in the presence and absence of BRL 37344 was identical. In current-clamp mode, BRL 37344 caused membrane potential hyperpolarization from −26.1 ± 2.1 mV (control) to −29.0 ± 2.2 mV. The BRL 37344-induced hyperpolarization was eliminated by application of iberiotoxin, tetraethylammonium or ryanodine. The data indicate that stimulation of β3-AR relaxes rat UBSM by increasing the BK channel STOC frequency, which causes membrane hyperpolarization and thus relaxation.

Download Full-text

Negative feedback regulation of nerve-mediated contractions by KCa channels in mouse urinary bladder smooth muscle

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00488.2004 ◽

2005 ◽

Vol 289 (2) ◽

pp. R402-R409 ◽

Cited By ~ 54

Author(s):

Gerald M. Herrera ◽

Bud Etherton ◽

Bernhard Nausch ◽

Mark T. Nelson

Keyword(s):

Smooth Muscle ◽

Urinary Bladder ◽

Negative Feedback ◽

Nerve Stimulation ◽

Bk Channels ◽

Bladder Smooth Muscle ◽

Parasympathetic Nerves ◽

Sk Channel ◽

Urinary Bladder Smooth Muscle ◽

Evoked Contractions

When the urinary bladder is full, activation of parasympathetic nerves causes release of neurotransmitters that induce forceful contraction of the detrusor muscle, leading to urine voiding. The roles of ion channels that regulate contractility of urinary bladder smooth muscle (UBSM) in response to activation of parasympathetic nerves are not well known. The present study was designed to characterize the role of large (BK)- and small-conductance (SK) Ca2+-activated K+ (KCa) channels in regulating UBSM contractility in response to physiological levels of nerve stimulation in UBSM strips from mice. Nerve-evoked contractions were induced by electric field stimulation (0.5–50 Hz) in isolated strips of UBSM. BK and SK channel inhibition substantially increased the amplitude of nerve-evoked contractions up to 2.45 ± 0.12- and 2.99 ± 0.25-fold, respectively. When both SK and BK channels were inhibited, the combined response was additive. Inhibition of L-type voltage-dependent Ca2+ channels (VDCCs) in UBSM inhibited nerve-evoked contractions by 92.3 ± 2.0%. These results suggest that SK and BK channels are part of two distinct negative feedback pathways that limit UBSM contractility in response to nerve stimulation by modulating the activity of VDCCs. Dysfunctional regulation of UBSM contractility by alterations in BK/SK channel expression or function may underlie pathologies such as overactive bladder.

Download Full-text

Expression and functional role of Rho-kinase in rat urinary bladder smooth muscle

British Journal of Pharmacology ◽

10.1038/sj.bjp.0705109 ◽

2003 ◽

Vol 138 (5) ◽

pp. 757-766 ◽

Cited By ~ 125

Author(s):

Alexandra Wibberley ◽

Zunxuan Chen ◽

Erding Hu ◽

J Paul Hieble ◽

Timothy D Westfall

Keyword(s):

Smooth Muscle ◽

Urinary Bladder ◽

Functional Role ◽

Rho Kinase ◽

Bladder Smooth Muscle ◽

Rat Urinary Bladder ◽

Urinary Bladder Smooth Muscle

Download Full-text

Voltage-gated K+ channels sensitive to stromatoxin-1 regulate myogenic and neurogenic contractions of rat urinary bladder smooth muscle

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00036.2010 ◽

2010 ◽

Vol 299 (1) ◽

pp. R177-R184 ◽

Cited By ~ 20

Author(s):

Muyan Chen ◽

Whitney F. Kellett ◽

Georgi V. Petkov

Keyword(s):

Smooth Muscle ◽

Urinary Bladder ◽

Electrical Field Stimulation ◽

Resting Membrane Potential ◽

Bladder Smooth Muscle ◽

Membrane Excitability ◽

Molecular Fingerprints ◽

Rat Urinary Bladder ◽

Voltage Gated ◽

Urinary Bladder Smooth Muscle

Members of the voltage-gated K+ (KV) channel family are suggested to control the resting membrane potential and the repolarization phase of the action potential in urinary bladder smooth muscle (UBSM). Recent studies report that stromatoxin-1, a peptide isolated from tarantulas, selectively inhibits KV2.1, KV2.2, KV4.2, and KV2.1/9.3 channels. The objective of this study was to investigate whether KV channels sensitive to stromatoxin-1 participate in the regulation of rat UBSM contractility and to identify their molecular fingerprints. Stromatoxin-1 (100 nM) increased the spontaneous phasic contraction amplitude, muscle force, and tone in isolated UBSM strips. However, stromatoxin-1 (100 nM) had no effect on the UBSM contractions induced by depolarizing agents such as KCl (20 mM) or carbachol (1 μM). This indicates that, under conditions of sustained membrane depolarization, the KV channels sensitive to stromatoxin-1 have no further contribution to the membrane excitability and contractility. Stromatoxin-1 (100 nM) increased the amplitude of the electrical field stimulation-induced contractions, suggesting also a role for these channels in neurogenic contractions. RT-PCR experiments on freshly isolated UBSM cells showed mRNA expression of KV2.1, KV2.2, and KV9.3, but not KV4.2 channel subunits. Protein expression of KV2.1 and KV2.2 channels was detected using Western blot and was further confirmed by immunocytochemical detection in freshly isolated UBSM cells. These novel findings indicate that KV2.1 and KV2.2, but not KV4.2, channel subunits are expressed in rat UBSM and play a key role in opposing both myogenic and neurogenic UBSM contractions.

Download Full-text

Regulation of urinary bladder smooth muscle contractions by ryanodine receptors and BK and SK channels

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.2000.279.1.r60 ◽

2000 ◽

Vol 279 (1) ◽

pp. R60-R68 ◽

Cited By ~ 113

Author(s):

Gerald M. Herrera ◽

Thomas J. Heppner ◽

Mark T. Nelson

Keyword(s):

Smooth Muscle ◽

Urinary Bladder ◽

Negative Feedback ◽

Ryanodine Receptors ◽

Bk Channels ◽

Sk Channels ◽

Bladder Smooth Muscle ◽

Contraction Amplitude ◽

Contraction Frequency ◽

Urinary Bladder Smooth Muscle

This study examines the roles of voltage-dependent Ca2+ channels (VDCC), ryanodine receptors (RyRs), large-conductance Ca2+-activated K+ (BK) channels, and small-conductance Ca2+-activated K+ (SK) channels in the regulation of phasic contractions of guinea pig urinary bladder smooth muscle (UBSM). Nisoldipine (100 nM), a dihydropyridine inhibitor of VDCC, abolished spontaneous UBSM contractions. Ryanodine (10 μM) increased contraction frequency and thereby integrated force and, in the presence of the SK blocker apamin, had a greater effect on integrated force than ryanodine alone. Blocking BK (iberiotoxin, 100 nM) or SK (apamin, 100 nM) channels increased contraction amplitude and duration but decreased frequency. The contractile response to iberiotoxin was more pronounced than to apamin. The increases in contraction amplitude and duration to apamin were substantially augmented with ryanodine pretreatment. These results indicate that BK and SK channels have prominent roles as negative feedback elements to limit UBSM contraction amplitude and duration. RyRs also appear to play a significant role as a negative feedback regulator of contraction frequency and duration, and this role is influenced by the activity of SK channels.

Download Full-text