KCNQ-encoded Kv7 Voltage-gated Potassium Channels: Presence and Functional Role in Human Vasculature

Fu Liang Ng1,2, Shuk Yin Yeung1, Andrew Wan2, Marcus Reddy2, David Melville2, Soren-Peter Olesen3,4, Teck Khong1,2, Iain Greenwood1. 1St. George’s, University of London, London, United Kingdom, 2St. George’s Hospital, London, United Kingdom, 3University of Copenhagen, Copenhagen, Denmark, 4NeuroSearch A/S, Ballerup, Denmark.

Background: KCNQ-encoded Kv7 voltage-gated potassium channels have previously been identified in neuronal and cardiac tissue. Recently, it has been identified in rat and mouse blood vessels, but as yet not in humans.

Methods: 35 resistance arteries from visceral adipose tissue were obtained from subjects undergoing elective surgery. Reverse transcriptase polymerase chain reaction (RT-PCR) experiments were undertaken using primers specific for all known KCNQ genes. Immunohistochemistry experiments were undertaken with antibodies specific to Kv7.1 and Kv7.4. Ex vivo pharmacological experiments with Kv7 channel activators and blockers assessed the impact on arterial smooth muscle by small vessel wire myography.

Results: The KCNQ genes have been found to be variably expressed in human resistance arteries whereby KCNQ4 expression was found in all 10 assessed arteries. This was followed KCNQ3, KCNQ5 and KCNQ1 in descending order of frequency. KCNQ2 expression has not been detected in this cohort. Immunohistochemistry experiments identified Kv7.1 and Kv7.4 proteins in sections of dissected arteries. Two structurally dissimilar Kv7 channel blockers, 10μM XE991 and 10μM linopiridine produced a constrictor response (equivalent to 73.1±18.4% and 22.3±11.6 of the response to 60mM KCl, n=27 and 16 respectively). The Kv7.1-specific blocker chromanol 293B did not produce a constrictor response. Two structurally dissimilar Kv7 channel activators were able to dose-dependently relax pre-constricted vessel segments – retigabine (3μM 45.3±11.0%, 10μM 78.9±6.9%, n=15) and acrylamide S-1 (3μM 83.3±5.1%, 10μM 93.3±4.6%, n=15). Reversal was achieved by 10μM XE991 in all vessels. 10μM acrylamide S-1 also suppressed spontaneous contractile activity in 5 vessel segments, reversible by 10μM XE991.

Conclusion: Our results are the first to demonstrate the presence of KCNQ mRNA in human vascular smooth muscle and that pharmacological modulation of Kv7 channels affects vascular tone ex vivo.