The unique N-terminal sequence of the BKCa channel α-subunit determines its modulation by β-subunits

Ion Channels Remodeling in the Regulation of Vascular Hyporesponsiveness During Shock

Shock is characterized with vascular hyporesponsiveness to vasoconstrictors, thereby to cause refractory hypotension, insufficient tissue perfusion, and multiple organ dysfunction. The vascular hyporeactivity persisted even though norepinephrine and fluid resuscitation were administrated, it is of critical importance to find new potential target. Ion channels are crucial in the regulation of cell membrane potential and affect vasoconstriction and vasodilation. It has been demonstrated that many types of ion channels including K+ channels, Ca2+ permeable channels, and Na+ channels exist in vascular smooth muscle cells and endothelial cells, contributing to the regulation of vascular homeostasis and vasomotor function. An increasing number of studies suggested that the structural and functional alterations of ion channels located in arteries contribute to vascular hyporesponsiveness during shock, but the underlying mechanisms remained to be fully clarified. Therefore, the expression and functional changes in ion channels in arteries associated with shock are reviewed, to pave the way for further exploring the potential of ion channel-targeted compounds in treating refractory hypotension in shock.

Oxytocin can regulate myometrial smooth muscle excitability by inhibiting the Na+ -activated K+ channel, Slo2.1

KEY POINTS

At the end of pregnancy, the uterus transitions from a quiescent state to a highly contractile state. This transition requires that the uterine (myometrial) smooth muscle cells increase their excitability, although how this occurs is not fully understood. We identified SLO2.1, a potassium channel previously unknown in uterine smooth muscle, as a potential significant contributor to the electrical excitability of myometrial smooth muscle cells. We found that activity of the SLO2.1 channel is negatively regulated by oxytocin via Gαq-protein-coupled receptor activation of protein kinase C. This results in depolarization of the uterine smooth muscle cells and calcium entry, which may contribute to uterine contraction. These findings provide novel insights into a previously unknown mechanism by which oxytocin may act to modulate myometrial smooth muscle cell excitability. Our findings also reveal a new potential pharmacological target for modulating uterine excitability.

ABSTRACT

During pregnancy, the uterus transitions from a quiescent state to a more excitable contractile state. This is considered to be at least partly a result of changes in the myometrial smooth muscle cell (MSMC) resting membrane potential. However, the ion channels controlling the myometrial resting membrane potential and the mechanism of transition to a more excitable state have not been fully clarified. In the present study, we show that the sodium-activated, high-conductance, potassium leak channel, SLO2.1, is expressed and active at the resting membrane potential in MSMCs. Additionally, we report that SLO2.1 is inhibited by oxytocin binding to the oxytocin receptor. Inhibition of SLO2.1 leads to membrane depolarization and activation of voltage-dependent calcium channels, resulting in calcium influx. The results of the present study reveal that oxytocin may modulate MSMC electrical activity by inhibiting SLO2.1 potassium channels.

Voltage-gated calcium channel α 2δ subunits: an assessment of proposed novel roles

Voltage-gated calcium (Ca_V) channels are associated with β and α₂δ auxiliary subunits. This review will concentrate on the function of the α₂δ protein family, which has four members. The canonical role for α₂δ subunits is to convey a variety of properties on the Ca_V1 and Ca_V2 channels, increasing the density of these channels in the plasma membrane and also enhancing their function. More recently, a diverse spectrum of non-canonical interactions for α₂δ proteins has been proposed, some of which involve competition with calcium channels for α₂δ or increase α₂δ trafficking and others which mediate roles completely unrelated to their calcium channel function. The novel roles for α₂δ proteins which will be discussed here include association with low-density lipoprotein receptor-related protein 1 (LRP1), thrombospondins, α-neurexins, prion proteins, large conductance (big) potassium (BK) channels, and N-methyl-d-aspartate (NMDA) receptors.