Identification of sodium/myo-inositol transporter 1 as a major determinant of arterial contractility

Background As the sodium/ myoinositol transporter (SMIT1) is a positive regulator of Kv7.4/7.5 channels in arterial smooth muscle we postulated that altering SMIT1 expression could have a major impact upon vascular reactivity. Consequently, this study aimed to characterise the effects of changes of SMIT1 membrane abundance on vascular tone and the molecular mechanisms involved. Methods Isometric tension recording on 2 nd order mesenteric arteries and left anterior coronary arteries from male and female Wistar Han rats. Whole artery membrane potential recording. Single cell and whole artery antibody-based imaging. Morpholino based protein knockdown of SMIT1. Results Morpholino-mediated knockdown of SMIT1 enhanced U46619- and methoxamine-mediated contractions of mesenteric artery whilst impairing relaxations to the Kv7 activator ML213, isoprenaline and CGRP. Conversely, augmenting SMIT1 membrane abundance by raising external osmolarity with 150 mM raffinose, impaired receptor-mediated contractions of mesenteric and coronary arteries, augmented relaxations to ML213 and adenosine as well as producing membrane potential hyperpolarisation. Proximity ligation assays revealed that raffinose incubation increased the association of SMIT-Kv7.4/7.5 as well as Kv7.4 and Gβγ subunits. The SGK1 inhibitor EMD638683 prevented the raffinose-induced increase in SMIT1 and the anti-contractile effect. Conclusion Toggling the membrane abundance of SMIT1 had a dramatic effect on the arterial response to vasonstrictors and vasodilators mediated by greater coordination of Kv7 channels and Gβγ subunits. This work identified SMT1-Kv7 channel complexes and SGK1 regulation as key modulators of arterial responsiveness.