Vascular Kv7 channels control intracellular Ca2+ dynamics in smooth muscle

Abstract

Voltage-gated Kv7 (or KCNQ) channels control activity of excitable cells, including vascular smooth muscle cells (VSMCs), by setting their resting membrane potential and controlling other excitability parameters. Excitation-contraction coupling in muscle cells is mediated by Ca²⁺ but until now, the exact role of Kv7 channels in cytosolic Ca²⁺ dynamics in VSMCs has not been fully elucidated. We utilised microfluorimetry to investigate the impact of Kv7 channel activity on intracellular Ca²⁺ levels and electrical activity of rat A7r5 VSMCs and primary human internal mammary artery (IMA) SMCs. Both, direct (XE991) and G protein coupled receptor mediated (vasopressin, AVP) Kv7 channel inhibition induced robust Ca²⁺ oscillations, which were significantly reduced in the presence of Kv7 channel activator, retigabine, L-type Ca²⁺ channel inhibitor, nifedipine, or T-type Ca²⁺ channel inhibitor, NNC 55-0396, in A7r5 cells. Membrane potential measured using FluoVolt exhibited a slow depolarisation followed by a burst of sharp spikes in response to XE991; spikes were temporally correlated with Ca²⁺ oscillations. Phospholipase C inhibitor (edelfosine) reduced AVP-induced, but not XE991-induced Ca²⁺ oscillations. AVP and XE991 induced a large increase of [Ca²⁺]_i in human IMA, which was also attenuated with retigabine, nifedipine and NNC 55-0396. RT-PCR, immunohistochemistry and electrophysiology suggested that Kv7.5 was the predominant Kv7 subunit in both rat and human arterial SMCs; CACNA1C (Cav1.2; L-type) and CACNA1 G (Cav3.1; T-type) were the most abundant voltage-gated Ca²⁺ channel gene transcripts in both types of VSMCs. This study establishes Kv7 channels as key regulators of Ca²⁺ signalling in VSMCs with Kv7.5 playing a dominant role.

Keywords: Calcium; Kv7; Phospholipase C; Retigabine; T-type Ca(2+)channels; Vascular smooth muscle cell; Vasopressin.