Rad-mediated inhibition of Ca1.2 channel activity contributes to uterine artery haemodynamic adaptation to pregnancy.

The striking increase of uterine blood flow during pregnancy is essential for normal fetal development as well as for cardiovascular well-being of the mother. Yet, the underlying mechanisms of pregnancy-mediated vasodilatation of the uterine artery are not fully understood. In this study, we test the hypothesis that Rad, a monomeric G protein, is a novel regulatory mechanism in inhibiting Ca1.2 channel currents in uterine artery haemodynamic adaptation to pregnancy in a sheep model. We found that pregnancy significantly upregulates Rad expression and decreases Ca1.2 channel currents in uterine arterial smooth muscle cells. Rad knockdown ex vivo and in vivo increases Ca1.2 activity and channel window currents by reducing steady-state inactivation in uterine arteries of pregnant sheep, recapitulating the phenotype of uterine arteries in non-pregnant animals. Moreover, Rad knockdown in vivo in pregnant sheep enhances myogenic tone and phenylephrine-induced vasoconstriction of uterine arteries. Whereas knockdown of Rad has no effect on mesenteric arterial Ca1.2 channel activity and mean arterial blood pressure, it significantly increases uterine vascular resistance and decreases uterine artery blood flow. Our study reveals a novel cause-and-effect mechanism of Rad in pregnancy-induced suppression of Ca1.2 channel activity in uterine arteries to facilitate increased uterine blood flow, providing new insights into fundamental mechanisms of uterine haemodynamic adaptation to pregnancy. KEY POINTS: Pregnancy suppresses Ca1.2 channel currents in uterine arterial smooth muscle cells. Rad, a monomeric G protein, is upregulated in uterine arteries of pregnant sheep. Rad knockdown ex vivo or in vivo increases Ca1.2 channel currents in uterine arteries from pregnant ewes. In vivo knockdown of Rad elevates uterine vascular resistance and decreases uterine blood flow in pregnant sheep. The study reveals a novel mechanism of Rad in pregnancy-induced suppression of Ca1.2 channel activity in uterine arterial haemodynamic adaptation to pregnancy.