Roles of ion channels in regulation of acetylcholine-mediated vasoconstrictions in umbilical cords of rabbit/rats

Downregulation of large-conductance Ca2+-activated K+ channels in human umbilical arterial smooth muscle cells in gestational diabetes mellitus

AIMS

We investigated the changes in large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels from human umbilical arterial smooth muscle cells experiencing gestational diabetes mellitus (GDM).

MAIN METHODS

Whole-cell patch-clamp technique, arterial tone measurement, RT-PCR, Quantitative real-time PCR, western blot were performed in human umbilical arterial smooth muscle cells.

KEY FINDINGS

Whole-cell BK_Ca current density was decreased in the GDM group compared with the normal group. The vasorelaxant effects of the synthetic BK_Ca channel activator NS-1619 (10 μM) were impaired in the GDM group compared with the normal group. Reverse-transcription polymerase chain reaction (RT-PCR), real-time RT-PCR, and western blot analyses suggested that the mRNA, total RNA, and protein expression levels of the BK_Ca channel were decreased in the GDM group relative to the normal group. In addition, the expression levels of protein kinase A and protein kinase G, which regulate BK_Ca channel activity, remained unchanged between the groups. Applying the BK_Ca channel inhibitor paxilline (10 μM) induced vasoconstriction and membrane depolarization of isolated umbilical arteries in the normal group but showed less of an effect on umbilical arteries in the GDM group.

SIGNIFICANCE

Our results demonstrate for the first time impaired BK_Ca current and BK_Ca channel-induced vasorelaxation activities that were not caused by impaired BK_Ca channel-regulated protein kinases, but by decreased expression of the BK_Ca channels, in the umbilical arteries of GDM patients.

Methylation-reprogrammed CHRM3 results in vascular dysfunction in the human umbilical vein following IVF-ET

Assisted reproductive technology (ART) has been used globally among infertile couples. However, many epidemiological investigations have indicated that ART is associated with a range of long-term adverse health outcomes in offspring, including cardiovascular disease, obesity and increased plasma lipid levels. Until now, direct evidence has been limited regarding the pathological changes in vascular function in fetuses with ART. In this study, human umbilical cords were collected from healthy normal pregnancies and IVF-ET pregnancies. Vascular functional studies involving acetylcholine (ACh), antagonists of its specific receptors, and L-type calcium channel/PKC-MLC20 phosphorylation pathway specific inhibitors were conducted. Quantitative real-time PCR, Western blotting and methylation analyses were performed on umbilical vein samples. We found that the umbilical vein constriction induced by ACh in the IVF-ET group was significantly attenuated compared with that in the healthy normal pregnancy group, which was not only associated with the hypermethylation of ACh muscarinic receptor subtype 3 (CHRM3) and decreased expression of CHRM3, PKCβ and CaV1.2, but was also related to the reduced phosphorylation of MLC20. The present study revealed that the hypermethylation of CHRM3, leading to a reduction in CHRM3 expression and downregulation of the CaV1.2/PKC-MLC20 phosphorylation pathway, was responsible for the decreased sensitivity to ACh observed in the umbilical vein under IVF-ET conditions. The hypermethylation of CHRM3 caused by IVF-ET might play an important role in altered vasoconstriction and impact cardiovascular systems in the long run.

Novel insights for the role of nitric oxide in placental vascular function during and beyond pregnancy

More than 30 years have passed since endothelial nitric oxide synthesis was described using the umbilical artery and vein endothelium. That seminal report set the cornerstone for unveiling the molecular aspects of endothelial function. In parallel, the understanding of placental physiology has gained growing interest, due to its crucial role in intrauterine development, with considerable long-term health consequences. This review discusses the evidence for nitric oxide (NO) as a critical player of placental development and function, with a special focus on endothelial nitric oxide synthase (eNOS) vascular effects. Also, the regulation of eNOS-dependent vascular responses in normal pregnancy and pregnancy-related diseases and their impact on prenatal and postnatal vascular health are discussed. Recent and compelling evidence has reinforced that eNOS regulation results from a complex network of processes, with novel data concerning mechanisms such as mechano-sensing, epigenetic, posttranslational modifications, and the expression of NO- and l-arginine-related pathways. In this regard, most of these mechanisms are expressed in an arterial-venous-specific manner and reflect traits of the fetal systemic circulation. Several studies using umbilical endothelial cells are not aimed to understand placental function but general endothelial function, reinforcing the influence of the placenta on general knowledge in physiology.

Clinical Importance of the Human Umbilical Artery Potassium Channels

Potassium (K⁺) channels are usually predominant in the membranes of vascular smooth muscle cells (SMCs). These channels play an important role in regulating the membrane potential and vessel contractility-a role that depends on the vascular bed. Thus, the activity of K⁺ channels represents one of the main mechanisms regulating the vascular tone in physiological and pathophysiological conditions. Briefly, the activation of K⁺ channels in SMC leads to hyperpolarization and vasorelaxation, while its inhibition induces depolarization and consequent vascular contraction. Currently, there are four different types of K⁺ channels described in SMCs: voltage-dependent K⁺ (K_V) channels, calcium-activated K⁺ (K_Ca) channels, inward rectifier K⁺ (Kir) channels, and 2-pore domain K⁺ (K_2P) channels. Due to the fundamental role of K⁺ channels in excitable cells, these channels are promising therapeutic targets in clinical practice. Therefore, this review discusses the basic properties of the various types of K⁺ channels, including structure, cellular mechanisms that regulate their activity, and new advances in the development of activators and blockers of these channels. The vascular functions of these channels will be discussed with a focus on vascular SMCs of the human umbilical artery. Then, the clinical importance of K⁺ channels in the treatment and prevention of cardiovascular diseases during pregnancy, such as gestational hypertension and preeclampsia, will be explored.

Acetylcholine attenuated TNF-α-induced intracellular Ca2+ overload by inhibiting the formation of the NCX1-TRPC3-IP3R1 complex in human umbilical vein endothelial cells

The endoplasmic reticulum (ER) forms discrete junctions with the plasma membrane (PM) that play a critical role in the regulation of Ca²⁺ signaling during cellular bioenergetics, apoptosis and autophagy. We have previously confirmed that acetylcholine can inhibit ER stress and apoptosis after inflammatory injury. However, limited research has focused on the effects of acetylcholine on ER-PM junctions. In this work, we evaluated the structure and function of the supramolecular sodium-calcium exchanger 1 (NCX1)-transient receptor potential canonical 3 (TRPC3)-inositol 1,4,5-trisphosphate receptor 1 (IP3R1) complex, which is involved in regulating Ca²⁺ homeostasis during inflammatory injury. The width of the ER-PM junctions of human umbilical vein endothelial cells (HUVECs) was measured in nanometres using transmission electron microscopy and a fluorescent probe for Ca²⁺. Protein-protein interactions were assessed by immunoprecipitation. Ca²⁺ concentration was measured using a confocal microscope. An siRNA assay was employed to silence specific proteins. Our results demonstrated that the peripheral ER was translocated to PM junction sites when induced by tumour necrosis factor-alpha (TNF-α) and that NCX1-TRPC3-IP3R1 complexes formed at these sites. After down-regulating the protein expression of NCX1 or IP3R1, we found that the NCX1-mediated inflow of Ca²⁺ and the release of intracellular Ca²⁺ stores were reduced in TNF-α-treated cells. We also observed that acetylcholine attenuated the formation of NCX1-TRPC3-IP3R1 complexes and maintained calcium homeostasis in cells treated with TNF-α. Interestingly, the positive effects of acetylcholine were abolished by the selective M3AChR antagonist darifenacin and by AMPK siRNAs. These results indicate that acetylcholine protects endothelial cells from TNF-alpha-induced injury, [Ca²⁺]_cyt overload and ER-PM interactions, which depend on the muscarinic 3 receptor/AMPK pathway, and that acetylcholine may be a new inhibitor for suppressing [Ca²⁺]_cyt overload.