Functional expression of KCNQ (K_v7) channels in guinea pig bladder smooth muscle and their contribution to spontaneous activity

Abstract

Background and PurposeThe aim of the study was to determine whether KCNQ channels are functionally expressed in bladder smooth muscle cells (SMC) and to investigate their physiological significance in bladder contractility.Experimental ApproachKCNQ channels were examined at the genetic, protein, cellular and tissue level in guinea pig bladder smooth muscle using RT-PCR, immunofluorescence, patch-clamp electrophysiology, calcium imaging, detrusor strip myography, and a panel of KCNQ activators and inhibitors.Key ResultsKCNQ subtypes 1–5 are expressed in bladder detrusor smooth muscle. Detrusor strips typically displayed TTX-insensitive myogenic spontaneous contractions that were increased in amplitude by the KCNQ channel inhibitors XE991, linopirdine or chromanol 293B. Contractility was inhibited by the KCNQ channel activators flupirtine or meclofenamic acid (MFA). The frequency of Ca2+-oscillations in SMC contained within bladder tissue sheets was increased by XE991. Outward currents in dispersed bladder SMC, recorded under conditions where BK and KATP currents were minimal, were significantly reduced by XE991, linopirdine, or chromanol, and enhanced by flupirtine or MFA. XE991 depolarized the cell membrane and could evoke transient depolarizations in quiescent cells. Flupirtine (20 μM) hyperpolarized the cell membrane with a simultaneous cessation of any spontaneous electrical activity.Conclusions and ImplicationsThese novel findings reveal the role of KCNQ currents in the regulation of the resting membrane potential of detrusor SMC and their important physiological function in the control of spontaneous contractility in the guinea pig bladder.

KV7 channels contribute to paracrine, but not metabolic or ischemic, regulation of coronary vascular reactivity in swine

“…The first description of K V 7 channels in vascular smooth muscle was made over a decade ago, when KCNQ1 and a novel splice variant, KCNQ1b, were observed in the mouse portal vein (29,35). Since that seminal observation, it has been found that KCNQ isoforms are also expressed in gastrointestinal, myometrium, airway, and bladder smooth muscle (1,7,17,29). K V 7 channels can be homo-or heterotetramers; however, data regarding which subunits can form heteromers in vascular tissues is recent (10), and we do not yet know the exact subunit composition of K V 7 channels in swine coronary vascular smooth muscle.…”

The Novel KV7.2/KV7.3 Channel Opener ICA-069673 Reveals Subtype-Specific Functional Roles in Guinea Pig Detrusor Smooth Muscle Excitability and Contractility

“…at ASPET Journals on May 7, 2018 jpet.aspetjournals.org tissue via immunohistochemistry (Afeli et al, 2013;Anderson et al, 2013), which has the inherent limitation of potentially detecting K V 7 channel expression from neighboring non-DSM cell types such as neurons or interstitial cells in the absence of cell-specific labeling. Thus, as illustrated in Fig.…”

“…K V 7 channel inhibition with XE991 was associated with membrane depolarization and an increase in Ca 21 oscillations and phasic contractions in guinea pig DSM (Afeli et al, 2013;Anderson et al, 2013). K V 7 channel activation with retigabine caused membrane hyperpolarization and inhibition of DSM phasic contractions (Afeli et al, 2013).…”

“…In guinea pig DSM, mRNA transcripts for all K V 7 channel subunits have been identified (Anderson et al, 2013), with quantitative polymerase chain reaction studies indicating that K V 7.1, K V 7.2, and K V 7.5 channel a-subunits are most prevalent in DSM cells (Afeli et al, 2013). K V 7 channel inhibition with XE991 was associated with membrane depolarization and an increase in Ca 21 oscillations and phasic contractions in guinea pig DSM (Afeli et al, 2013;Anderson et al, 2013).…”

“…Voltage-gated K 1 (K V 7) channels (K V 7.1-K V 7.5), also known as KCNQ (KCNQ1-KCNQ5) channels, have been suggested as key regulators of detrusor smooth muscle (DSM) excitability and contractility Sheldon et al, 2002;Afeli et al, 2013;Anderson et al, 2013;Svalø et al, 2015). In DSM, the overall function of K V channels, which includes the K V 7 channels, is to maintain and stabilize the resting membrane potential (Petkov, 2012).…”