Connexin 40-Mediated Regulation of Systemic Circulation and Arterial Blood Pressure.

Vascular system is a complex network in which different cell types and vascular segments must work in concert to regulate blood flow distribution and arterial blood pressure. Although paracrine/autocrine signaling is involved in the regulation of vasomotor tone, direct intercellular communication via gap junctions plays a central role in the control and coordination of vascular function in the microvascular network. Gap junctions are made up by connexin (Cx) proteins, and among the four Cxs expressed in the cardiovascular system (Cx37, Cx40, Cx43, and Cx45), Cx40 has emerged as a critical signaling pathway in the vessel wall. This Cx is predominantly found in the endothelium, but it is involved in the development of the cardiovascular system and in the coordination of endothelial and smooth muscle cell function along the length of the vessels. In addition, Cx40 participates in the control of vasomotor tone through the transmission of electrical signals from the endothelium to the underlying smooth muscle and in the regulation of arterial blood pressure by renin-angiotensin system in afferent arterioles. In this review, we discuss the participation of Cx40-formed channels in the development of cardiovascular system, control and coordination of vascular function, and regulation of arterial blood pressure.

Impaired function of cerebral parenchymal arterioles in experimental preeclampsia.

Preeclampsia (PE), a dangerous hypertensive complication of pregnancy, is associated with widespread maternal vascular dysfunction. However, the effect of PE on the cerebral vasculature that can lead to stroke and cognitive decline is not well understood. We hypothesized that function of cortical parenchymal arterioles (PAs) would be impaired during PE. Using a high cholesterol diet to induce experimental PE in rats (ePE), we studied the function and structure of isolated and pressurized PAs supplying frontoparietal white matter (WM) tracts and cortex and compared to normal pregnant (Preg) and nonpregnant (Nonpreg) Sprague Dawley rats (n = 8/group). Myogenic reactivity and tone were similar between groups; however, constriction to intermediate-conductance calcium-activated potassium (IK) channel inhibition was diminished and dilation to inward-rectifying K+ (KIR) channel activation was impaired in PAs from ePE rats, suggesting altered ion channel function. Conducted vasodilation was significantly delayed in response to 12 mM KCl, but not 10 µM adenosine, in PAs from ePE rats versus Preg and Nonpreg rats (940 ±â€¯300 ms vs. 70 ±â€¯50 ms and 370 ±â€¯90 ms; p < 0.05). Overall, dysfunction of PAs supplying frontoparietal WM and gray matter was present in ePE. If persistent these changes could potentiate neuronal injury that over time could contribute to WM lesions and early-onset cognitive decline.

Ca2+ Signalling in Pericytes.

Microcirculation is the generic name for the finest level of the circulatory system and consists of arteriolar and venular networks located upstream and downstream of capillaries, respectively. Anatomically arterioles are surrounded by a monolayer of spindle-shaped smooth muscle cells (myocytes), while terminal branches of precapillary arterioles, capillaries and all sections of postcapillary venules are surrounded by a monolayer of morphologically different perivascular cells (pericytes). Pericytes are essential components of the microvascular vessel wall. Wrapped around endothelial cells, they occupy a strategic position at the interface between the circulating blood and the interstitial space. There are physiological differences in the responses of pericytes and myocytes to vasoactive molecules, which suggest that these two types of vascular cells could have different functional roles in the regulation of local blood flow within the same microvascular bed. Also, pericytes may play different roles in different microcirculatory beds to meet the characteristics of individual organs. Contractile activity of pericytes and myocytes is controlled by changes of cytosolic free Ca2+concentration. In this chapter, we attempt to summarize the results in the field of Ca2+ signalling in pericytes especially in light of their contractile roles in different tissues and organs. We investigate the literature and describe our results regarding sources of Ca2+, relative importance and mechanisms of Ca2+ release and Ca2+ entry in control of the spatio-temporal characteristics of the Ca2+ signals in pericytes, where possible Ca2+ signalling and contractile responses in pericytes are compared to those of myocytes.

Cardiovascular Functions of Ena/VASP Proteins: Past, Present and Beyond.

Actin binding proteins are of crucial importance for the spatiotemporal regulation of actin cytoskeletal dynamics, thereby mediating a tremendous range of cellular processes. Since their initial discovery more than 30 years ago, the enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) family has evolved as one of the most fascinating and versatile family of actin regulating proteins. The proteins directly enhance actin filament assembly, but they also organize higher order actin networks and link kinase signaling pathways to actin filament assembly. Thereby, Ena/VASP proteins regulate dynamic cellular processes ranging from membrane protrusions and trafficking, and cell-cell and cell-matrix adhesions, to the generation of mechanical tension and contractile force. Important insights have been gained into the physiological functions of Ena/VASP proteins in platelets, leukocytes, endothelial cells, smooth muscle cells and cardiomyocytes. In this review, we summarize the unique and redundant functions of Ena/VASP proteins in cardiovascular cells and discuss the underlying molecular mechanisms.

Signaling and structures underpinning conducted vasodilation in human and porcine intramyocardial coronary arteries.

Background: Adequate blood flow into coronary micro-arteries is essential for myocardial function. Here we assess the mechanisms responsible for amplifying blood flow into myogenically-contracting human and porcine intramyocardial micro-arteries ex vivo using endothelium-dependent and -independent vasodilators. Methods: Human and porcine atrial and ventricular small intramyocardial coronary arteries (IMCAs) were studied with pressure myography and imaged using confocal microscopy and serial section/3-D reconstruction EM. Results: 3D rendered ultrastructure images of human right atrial (RA-) IMCAs revealed extensive homo-and hetero-cellular contacts, including to longitudinally-arranged smooth muscle cells (l-SMCs) found between the endothelial cells (ECs) and radially-arranged medial SMCs (r-SMCs). Local and conducted vasodilatation followed focal application of bradykinin in both human and porcine RA-IMCAs, and relied on hyperpolarization of SMCs, but not nitric oxide. Bradykinin initiated asynchronous oscillations in endothelial cell Ca2+ in pressurized RA-IMCAs and, as previously shown in human RA-IMCAs, hyperpolarized porcine arteries. Immunolabelling showed small- and intermediate-conductance Ca2+-activated K+ channels (KCa) present in the endothelium of both species, and concentration-dependent vasodilation to bradykinin followed activation of these KCa channels. Extensive electrical coupling was demonstrated between r-SMCs and l-SMCs, providing an additional pathway to facilitate the well-established myoendothelial coupling. Conducted dilation was still evident in a human RA-IMCA with poor myogenic tone, and heterocellular contacts were visible in the 3D reconstructed artery. Hyperpolarization and conducted vasodilation was also observed to adenosine which, in contrast to bradykinin, was sensitive to combined block of ATP-sensitive (KATP) and inwardly rectifying (KIR) K+ channels. Conclusions: These data extend our understanding of the mechanisms that coordinate human coronary microvascular blood flow and the mechanistic overlap with porcine IMCAs. The unusual presence of l-SMCs provides an additional pathway for rapid intercellular signaling between cells of the coronary artery wall. Local and conducted vasodilation follow hyperpolarization of the ECs or SMCs, and contact-coupling between l-SMCs and r-SMCs likely facilitates this vasodilation.

Brain endothelial cell TRPA1 channels initiate neurovascular coupling.

Cerebral blood flow is dynamically regulated by neurovascular coupling to meet the dynamic metabolic demands of the brain. We hypothesized that TRPA1 channels in capillary endothelial cells are stimulated by neuronal activity and instigate a propagating retrograde signal that dilates upstream parenchymal arterioles to initiate functional hyperemia. We find that activation of TRPA1 in capillary beds and post-arteriole transitional segments with mural cell coverage initiates retrograde signals that dilate upstream arterioles. These signals exhibit a unique mode of biphasic propagation. Slow, short-range intercellular Ca2+ signals in the capillary network are converted to rapid electrical signals in transitional segments that propagate to and dilate upstream arterioles. We further demonstrate that TRPA1 is necessary for functional hyperemia and neurovascular coupling within the somatosensory cortex of mice in vivo. These data establish endothelial cell TRPA1 channels as neuronal activity sensors that initiate microvascular vasodilatory responses to redirect blood to regions of metabolic demand.

Hyperglycaemia disrupts conducted vasodilation in the resistance vasculature of db/db mice.

Vascular dysfunction in small resistance arteries is observed during chronic elevations in blood glucose. Hyperglycaemia-associated effects on endothelium-dependent vasodilation have been well characterized, but effects on conducted vasodilation in the resistance vasculature are not known. Small mesenteric arteries were isolated from healthy and diabetic db/db mice, which were used as a model of chronic hyperglycaemia. Endothelium-dependent vasodilation via the Gq/11-coupled proteinase activated receptor 2 (PAR2) was stimulated with the selective agonist SLIGRL. The Ca2+-sensitive fluorescent indicator fluo-8 reported changes in endothelial cell (EC) [Ca2+]i, and triple cannulated bifurcating mesenteric arteries were used to study conducted vasodilation. Chronic hyperglycaemia did not affect either EC Ca2+ or local vasodilation to SLIGRL. However, both acute and chronic exposure to high glucose or the mannitol osmotic control attenuated conducted vasodilation to 10µM SLIGRL. This investigation demonstrates for the first time that a hypertonic solution containing glucose or mannitol can interfere with the spread of a hyperpolarizing current along the endothelium in a physiological setting. Our findings reiterate the importance of studying the effects of hyperglycaemia in the vasculature, and provide the basis for further studies regarding the modulation of junctional proteins involved in cell to cell communication by diseases such as diabetes.