Abstract
Voltage-gated Kv7 (KCNQ) channels are emerging as essential regulators of smooth muscle excitability and contractility. However, their physiological role in detrusor smooth muscle (DSM) remains to be elucidated. Here, we explored the molecular expression and function of Kv7 channel subtypes in guinea pig DSM by RT-PCR, qRT-PCR, immunohistochemistry, electrophysiology, and isometric tension recordings. In whole DSM tissue, mRNAs for all Kv7 channel subtypes were detected in a rank order: Kv7.1~Kv7.2Kv7.3~Kv7.5Kv7.4. In contrast, freshly-isolated DSM cells showed mRNA expression of: Kv7.1~Kv7.2Kv7.5Kv7.3~Kv7.4. Immunohistochemical confocal microscopy analyses of DSM, conducted by using co-labeling of Kv7 channel subtype-specific antibodies and α-smooth muscle actin, detected protein expression for all Kv7 channel subtypes, except for the Kv7.4, in DSM cells. L-364373 (R-L3), a Kv7.1 channel activator, and retigabine, a Kv7.2-7.5 channel activator, inhibited spontaneous phasic contractions and the 10-Hz electrical field stimulation (EFS)-induced contractions of DSM isolated strips. Linopiridine and XE991, two pan-Kv7 (effective at Kv7.1-Kv7.5 subtypes) channel inhibitors, had opposite effects increasing DSM spontaneous phasic and 10 Hz EFS-induced contractions. EFS-induced DSM contractions generated by a wide range of stimulation frequencies were decreased by L-364373 (10 µM) or retigabine (10 µM), and increased by XE991 (10 µM). Retigabine (10 µM) induced hyperpolarization and inhibited spontaneous action potentials in freshly-isolated DSM cells. In summary, Kv7 channel subtypes are expressed at mRNA and protein levels in guinea pig DSM cells. Their pharmacological modulation can control DSM contractility and excitability; therefore, Kv7 channel subtypes provide potential novel therapeutic targets for urinary bladder dysfunction.
Highlights
The physiological roles of voltage-gated K+ (Kv) channels are emerging [1,2,3,4,5,6,7]
RT-PCR and qRT-PCR experiments demonstrate the expression of Kv7 channel subtypes in guinea pig detrusor smooth muscle (DSM)
We conducted RT-PCR and qRT-PCR experiments with whole DSM tissue and a pool of isolated DSM cells in order to investigate the expression of individual Kv7 channel subtypes at the mRNA level
Summary
The physiological roles of voltage-gated K+ (Kv) channels are emerging [1,2,3,4,5,6,7]. Evidence suggests that they might be critical regulators of detrusor smooth muscle (DSM) excitability and contractility [1,8]. Among the 40 genes encoding Kv channels identified in the human genome, the functions of the five pore-forming α subunits of the Kv7 subfamily are not well understood in DSM [9]. Kv7 channels may associate with regulatory β subunits encoded by KCNE genes (KCNE1-5) that fine-tune the functional and biophysical properties, and influence the plasma membrane expression of the Kv7 channel assemblies [12]
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