Efficacy, potency and kinetics of activation process of Kv7.4 and Kv7.5 channel with novel pharmacological activators targeted for Lower Urinary Tract Syndrome (LUTS)
Authors: Lee Jung , Kim Jinsung , So Insuk 
Published: April 2020

Among several types of Kv7 (KCNQ) voltage gated potassium channel family, Kv7.4 (KCNQ4) and Kv7.5 (KCNQ5) channels show prominent expression in smooth muscle, cardiac tissues and vasculature. In general, activation of the channel would mediate strong efflux of potassium and lead membrane potential to hyperpolarization, though the extent may depend on established potassium concentration gradient and membrane potential. Once membrane potential is hyperpolarized, it would decrease the excitability of excitable cells. Decreased excitability may reduce calcium spikes and Ca‐CaM mediated activation of myosin light chain kinase (MLCK) in smooth muscle cells. Recently, it was reported that Kv7.4 channels are highly expressed in corpus cavernosum smooth muscle cells and Kv7.5 channels in prostate smooth muscle cells, respectively. Since smooth muscle relaxation of corpus cavernosum and smooth muscle tension in prostate are in the center of pathophysiology of erectile dysfunction and LUTS, we examined the effect of novel Kv7.4 and Kv7.5 activators to the channel activation process.

In HEK293 cells expressing human Kv7.4 or Kv7.5 channels, we performed whole‐cell patch clamp technique with two different voltage protocols in order to measure specific activity of the channel. For kinetic analysis of the activation process, voltage steps from –100 mV to +100 mV with 10 mV of step interval was applied. For each step, pulse duration was 3 seconds for activation process of Kv7.4 and Kv7.5 channels is rather slow. Intersweep duration was 10 seconds and holding potential was –80 mV. For measurement of time‐dependent action of the drug, 10 seconds single step with +50 mV was applied in every 30s with holding potential of –80 mV. The composition of internal solution is as following; 120 KCl, 5.37 CaCl2, 1.75 MgCl2, 10 EGTA, 10 HEPES, 4 ATP, 0.2 GTP. pH was adjusted to 7.3 using KOH and [Ca2+]free = 100 nM. Normal tyrode solution was used for external solution and drugs stocked with DMSO was diluted to corresponding concentrations with the Normal tyrode solution.

We have found that URO‐K10, a novel activator, increases not only maximum conductance of the channel but also time constant of activation gate. In comparison to positive control, ML‐213, a well‐known Kv7.4 channel activator, URO‐K10 showed significant supremacy. EC50 of URO‐K10 was 0.304 ± 0.058 μM for Kv7.4 channel which is smaller than EC50 of ML‐213 (0.8 ± 0.3 μM). URO‐K10 not only increased the maximum conductance of the channel but also left‐shifted activation curve in terms of Boltzmann distribution. Half‐maximal voltage (V1/2) of Kv7.4 channel without any of the drugs was −43.03 mV whereas V1/2 of URO‐K10 activated channel was −67.65 mV, which is near the resting membrane potential of smooth muscle cells. ML‐213 activated channels showed V1/2 of −51.91 mV.

Support or Funding Information

This work was supported by the National Research Foundation of Korea, which is funded by the Ministry of Science, ICT (Information & Communication Technology), and Future Planning (MSIP) of the Korean Government (2018R1A41023822 to I. So) and by the Education and Research Encouragement Fund of Seoul National University Hospital (I. So). Jung Eun Lee was supported by the BK plus program from the MSIP.