Enhanced inhibition of the EDHF phenomenon by a phenyl methoxyalaninyl phosphoramidate derivative of dideoxyadenosine

Lead-induced cardiomyocytes apoptosis by inhibiting gap junction intercellular communication via autophagy activation

Lead (Pb) is one of the most common heavy metal contaminants in the environment. Pb can cause pathophysiological changes in several organ systems, including the cardiovascular system, but the molecular mechanism remains elusive. The study aimed to study the effects of Pb on Gap junction intercellular communication (GJIC) and its role in Pb-induced apoptosis. The present study aims to determine whether Pb-induced autophagy promotes apoptosis of rat cardiac myocytes (H9c2 cells) by downregulating GJIC using CCK-8 Kit, scrape loading/dye transfer assay, Annexin V/PI assays, Western blot analysis and double-immunofluorescence experiments. The results showed that Pb elicited cytotoxicity in a time- and concentration-dependent manner and led to increased apoptosis in a concentration-dependent manner in H9c2 cells. Pb also reduced GJIC in H9c2 cells in a concentration-dependent manner through the downregulation of connexin (Cx) 43. Inhibition of gap junctions by gap junction blocker carbenoxolone disodium (CBX) resulted in increased apoptosis. Furthermore, Pb increased autophagy in a concentration-dependent manner in H9c2 cells, decreasing the distribution of Cx43 on the cell membrane, and targeted Cx43 to autophagosome via light chain 3 (LC3). However, autophagy inhibitor 3-Methyladenine (3-MA) can slow down the downregulation of Cx43 induced by Pb in H9c2 cells. In conclusion, our results provide evidence that Pb-decreased GJIC promotes apoptosis in cardiomyocytes. This is probably because of the fact that Pb-induced autophagy exacerbates GJIC inhibition and downregulation of Cx43.

Acidosis potentiates endothelium-dependent vasorelaxation and gap junction communication in the superior mesenteric artery

Extracellular pH is an important physiological determinant of vascular tone that is normally maintained within 7.35-7.45. Any change outside this range leads to severe pathological repercussions. We investigated the unknown effects of extracellular acidosis on relaxation in the superior mesenteric artery (SMA) of goat. SMA rings were employed to maintain isometric contractions at extracellular pH (pH_o) 7.4 and 6.8. We analyzed the effect of acidosis (pH_o 6.8) compared to physiological pH (pH_o 7.4) on three signaling mediators of endothelium-dependent hyperpolarization: nitric oxide (NO), prostaglandin I₂ (PGI₂), and myoendothelial gap junctions (MEGJ). NO and cyclic guanosine monophosphate (cGMP) levels were compared between normal and acidic pH. Quantitative real-time PCR (qPCR) studies determined the change in expression of vascular connexin (Cx), Cx37, Cx40, and Cx43. Under acidosis, acetyl choline-induced relaxation was augmented in an endothelium-dependent manner via eNOS-NO-cGMP signaling. Conversely, at normal pH, acetyl choline-induced vasorelaxation was mediated primarily via COX-PGI₂ pathway. The functional activity of MEGJ was increased under acidosis as evident from increased sensitivity of connexin blockers and upregulated gene and protein expression of connexins. In conclusion, acetyl choline-induced augmented vasorelaxation under acidosis is mediated by NOS-NO-cGMP, with a partial role of MEGJ as EDH mediators in the SMA. Present data suggest a novel role of connexin as therapeutic targets to attenuate the detrimental effect of acidosis on vascular tone.

Interactions between thromboxane A₂, thromboxane/prostaglandin (TP) receptors, and endothelium-derived hyperpolarization

Endothelium-dependent smooth muscle hyperpolarization (EDH) increasingly predominates over endothelium-derived nitric oxide (NO) as a participant in vasodilation as vessel size decreases. Its underlying nature is highly variable between vessel types, species, disease states, and exact experimental conditions, and is variably mediated by one or more transferable endothelium-derived hyperpolarizing factors and/or the electrotonic spread of endothelial hyperpolarization into the media via gap junctions. Although generally regarded (and studied) as a mechanism that is independent of NO and prostanoids, evidence has emerged that the endothelium-derived contracting factor and prostanoid thromboxane A2 can modulate several signalling components central to EDH, and therefore potentially curtail vasodilation through mechanisms that are distinct from those putatively involved in direct smooth muscle contraction. Notably, vascular production of thromboxane A2 is elevated in a number of cardiovascular disease states that promote endothelial dysfunction. This review will therefore discuss the mechanisms through which thromboxane A2 interacts with and modulates EDH, and will also consider the implications of such cross-talk in vasodilator control in health and disease.

Intraluminal hyperglycaemia causes conduit and resistance artery dilatation and inhibits vascular autoregulation in the anaesthetised pig

The effect of intraluminal hyperglycaemia was investigated in the iliac artery of 11 anaesthetised pigs. Following isolation of a test segment, hyperglycaemic blood (40 mmol·L–1) caused a significant dilatation of the artery of 167 ± 208 μm (mean ± SD; n = 6, P = 0.031). Dilatations were reduced by N(G)-nitro-l-arginine methyl esther (250 μg·mL–1) from 145 ± 199 to 38 ± 5 μm), but this was not statistically significant (n = 6, P = 0.18). Intra-arterial infusions of d-glucose (20–40 mmol·L–1·min–1), during graded constrictions, caused statistically significant increases in blood flow (n = 11, P = 0.0013). Vasodilatation was confirmed by measurements of the ratio of immediate pressure steps to flow steps (∂P/∂F) during the graded obstruction experiments, showing a decrease in instantaneous vascular resistance from a control of 0.62 ± 0.30 to 0.33 ± 0.34 mm Hg·mL–1·min–1 (n = 7, P = 0.016). Autoregulation was assessed from the slopes of the plots of steady-state flow versus pressure. There were significant increases in the slope from 2.32 ± 1.03 to 5.88 ± 5.60 mL·min–1·(mm Hg)–1 (n = 7, P = 0.0078), indicating significant impairment of autoregulation. In conclusion, luminal hyperglycaemia relaxes both arterial and resistance vessel smooth muscle.

Capturing adenylyl cyclases as potential drug targets

Cyclic AMP (cAMP) is an important intracellular signalling mediator. It is generated in mammals by nine membrane-bound and one soluble adenylyl cyclases (ACs), each with distinct regulation and expression patterns. Although many drugs inhibit or stimulate AC activity through the respective upstream G-protein coupled receptors (for example, opioid or beta-adrenergic receptors), ACs themselves have not been major drug targets. Over the past decade studies on the physiological functions of the different mammalian AC isoforms as well as advances in the development of isoform-selective AC inhibitors and activators suggest that ACs could be useful drug targets. Here we discuss the therapeutic potential of isoform-selective compounds in various clinical settings, including neuropathic pain, neurodegenerative disorders, congestive heart failure, asthma and male contraception.

Endothelial influences on cerebrovascular tone

The cerebrovascular endothelium exerts a profound influence on cerebral vessels and cerebral blood flow. This review summarizes current knowledge of various dilator and constrictor mechanisms intrinsic to the cerebrovascular endothelium. The endothelium contributes to the resting tone of cerebral arteries and arterioles by tonically releasing nitric oxide (NO•). Dilations can occur by stimulated release of NO•, endothelium-derived hyperpolarization factor, or prostanoids. During pathological conditions, the dilator influence of the endothelium can turn to that of constriction by a variety of mechanisms, including decreased NO• bioavailability and release of endothelin-1. The endothelium may participate in neurovascular coupling by conducting local dilations to upstream arteries. Further study of the cerebrovascular endothelium is critical for understanding the pathogenesis of a number of pathological conditions, including stroke, traumatic brain injury, and subarachnoid hemorrhage.

Phosphoramidate derivatives of 2',5'-dideoxyadenosine as potential inhibitors of the EDHF phenomenon

P-site inhibitors of adenyl cyclase, such as the dideoxynucleosides 2',3'-ddA and 2',5-ddA, have been shown to attenuate EDHF phenomenon in rabbit arteries and veins. In order to present the dideoxynucleosides as pre-activated nucleotides and bypass the kinase, as well as to prevent their metabolism to dideoxyinosine by adenosine deaminase, the aryloxyphosphoramidate approach has been successfully applied, initially on the 2',3'-ddA. In the present work a new series of 2',5'-ddA phosphoramidates has been synthesized, representing the first example of phosphoramidate protide not at the 5'-position.

Connexin-mimetic peptides dissociate electrotonic EDHF-type signalling via myoendothelial and smooth muscle gap junctions in the rabbit iliac artery

Synthetic peptides corresponding to the Gap 26 and Gap 27 domains of the first and second extracellular loops of the major vascular connexins (Cx37, Cx40 and Cx43), designated as (43)Gap 26, (40)Gap 27, (37,40)Gap 26 and (37,43)Gap 27 according to Cx homology, were used to investigate the role of gap junctions in the spread of endothelial hyperpolarizations evoked by cyclopiazonic acid (CPA) through the wall of the rabbit iliac artery. Immunostaining and confocal microscopy demonstrated that gap junction plaques constructed from Cx37 and Cx40 were abundant in the endothelium, whereas Cx43 was the dominant Cx visualized in the media. None of the Cx-mimetic peptides affected endothelial hyperpolarizations evoked by CPA directly. When administered individually, (40)Gap 27, (37,40)Gap 26 and (37,43)Gap 27, but not (43)Gap 26, attenuated endothelium-dependent subintimal smooth muscle hyperpolarization. By contrast, only (43)Gap 26 and (37,43)Gap 27 reduced the spread of subintimal hyperpolarization through the media of the rabbit iliac artery. The site of action of the peptides therefore correlated closely with the expression of their target Cxs in detectable gap junction plaques. The findings provide further evidence that the EDHF phenomenon is electrotonic in nature, and highlight the contribution of myoendothelial and homocellular smooth muscle communication via gap junctions to arterial function.