Inhibitory effect of ammonium chloride on acetylcholine-induced relaxation

Editor's Highlight: Modifying Role of Endothelial Function Gene Variants on the Association of Long-Term PM2.5 Exposure With Blood DNA Methylation Age: The VA Normative Aging Study

Recent studies have reported robust associations of long-term PM2.5 exposure with DNA methylation-based measures of aging; yet, the molecular implications of these relationships remain poorly understood. We evaluated if genetic variation in 3 biological pathways implicated in PM2.5-related disease-oxidative stress, endothelial function, and metal processing-could modify the effect of PM2.5 on DNAm-age, one prominent DNA methylation-based measure of biological age. This analysis was based on 552 individuals from the Normative Aging Study with at least one visit between 2000 and 2011 (n = 940 visits). A genetic-score approach was used to calculate aging-risk variant scores for endothelial function, oxidative stress, and metal processing pathways. One-year PM2.5 and PM2.5 component (sulfate and ammonium) levels at participants' addresses were estimated using the GEOS-chem transport model. Blood DNAm-age was calculated using CpG sites on the Illumina HumanMethylation450 BeadChip. In fully-adjusted linear mixed-effects models, the effects of sulfate on DNAm-age (in years) were greater in individuals with high aging-risk endothelial function variant scores when compared with individuals with low aging-risk endothelial function variant scores (Pinteraction = 0.0007; βHigh = 1.09, 95% CIHigh: 0.70, 1.48; βLow = 0.40, 95% CILow: 0.14, 0.67). Similar trends were observed in fully adjusted models of ammonium and total PM2.5 alone. No effect modification was observed by oxidative stress and metal processing variant scores. Secondary analyses revealed significant associations of serum endothelial markers, intercellular adhesion molecule-1 (β = 0.01, 95% CI: 0.002, 0.012) and vascular cell adhesion molecule-1 (β = 0.002, 95% CI: 0.0005, 0.0026), with DNAm-age. Our results add novel evidence that endothelial physiology may be important to DNAm-age relationships, but further research is required to establish their generalizability.

Intracellular alkalinization augments capacitative Ca2+ entry in vascular smooth muscle cells

Agonist-induced Ca2+ influx of vascular smooth muscle cells is thought to be triggered by depletion of intracellular Ca2+ stores. This study investigated the effects of intracellular alkalinization on capacitative Ca2+ entry in A7r5 rat aortic smooth muscle cells. Intracellular alkalinization was induced by NH(4)Cl. Transplasmalemmal Ca2+ influx due to Ca2+ store depletion induced by thapsigargin, which was abolished by pretreatment of the cells with SKF-96365 but not affected by that with verapamil, was significantly increased by pretreatment with NH(4)Cl. Neither 5-hydroxytryptamine-induced inositol monophosphate accumulation nor intracellular Ca2+ release from its stores was affected by NH(4)Cl. These results suggest that intracellular alkalinization acts on the process(es) after depletion of Ca2+ stores and facilitates capacitative Ca2+ entry in vascular smooth muscle cells.

Angiotensin converting enzyme protects acetylcholine-induced relaxation from its attenuation by formyl-methionyl-leucyl-phenylalanine in rat aorta

OBJECTIVE

A chemotactic tripeptide formyl-methionyl-leucyl-phenylalanine (fMLP) attenuated acetylcholine (ACh)-induced relaxation. Because angiotensin converting enzyme (ACE), which inactivates fMLP, is rich in vascular endothelial cells, we examined whether endothelial cell ACE inhibits the attenuating effect of fMLP on ACh-induced relaxation.

DESIGN AND METHODS

ACh-induced relaxation was evaluated in aortic rings from 9-week-old Sprague-Dawley rats. We examined the effects of ACE, the ACE inhibitor captopril and/or fMLP on ACh-induced relaxation in aortas from rats with or without dexamethasone treatment, which enhances ACE activity.

RESULTS

Pre-treatment with ACE did not alter ACh-induced relaxation in control aortas but abolished the inhibitory effect of fMLP on ACh-induced relaxation [maximal relaxation (Emax): 95.4 +/- 1.2 versus 75.5 +/- 1.9%, P < 0.05]. Conversely, captopril enhanced the attenuation of ACh-induced relaxation by fMLP (Emax: 62.5 +/- 3.3 versus 74.0 +/- 2.2%, P < 0.05), although captopril did not affect ACh-induced relaxation in control aortas. In addition, fMLP did not attenuate ACh-induced relaxation in aortas from dexamethasone-treated rats (Emax: 89.7 +/- 3.7 versus 85.2 +/- 3.8%, NS), which enhanced ACE activity of aortas (3.37 +/- 0.25 versus 2.70 +/- 0.20 IU/mg protein, P < 0.05).

CONCLUSION

Endothelial-cell ACE attenuates the effect of fMLP on ACh-induced relaxation, possibly by its cleavage.

Cytosolic alkalinization of vascular endothelial cells produced by an abrupt reduction in fluid shear stress

Reductions in fluid shear stress produce endothelium-dependent vasoconstriction and promote neointimal hyperplasia, but the intracellular signaling mechanisms involved in these processes are poorly understood. To examine whether decreases in fluid shear stress affect endothelial cytosolic pH, carboxy-seminaphthorhodafluor-1-loaded rat aortic endothelial cells were cultured in glass microcapillary tubes and examined during abrupt reductions in laminar flow. After a 30-minute exposure to a shear stress of 2.7 dyne/cm2 in bicarbonate buffer, the acute reduction of fluid shear stress from 2.7 to 0.3 dyne/cm2 transiently increased cytosolic pH from 7.20+/-0.02 to 7.47+/-0.07 (mean+/-SEM, P<.05 versus control). This was not affected by prior inhibition of the Na+-H+ exchanger with 10 micromol/L ethylisopropylamiloride but was abolished in bicarbonate-free buffer. Recovery from an ammonium chloride prepulse-induced acid load occurred more rapidly when fluid shear stress was abruptly reduced from 2.7 to 0.3 dyne/cm2 after maximal acidification (+0.04+/-0.02 pH unit at 2 minutes) than when shear stress was maintained at 2.7 dyne/cm2 continuously (0.00+/-0.00 pH unit at 2 minutes, P<.05). This accelerated cytosolic pH recovery was dependent on the presence of bicarbonate ion and was blocked by the addition of the exchange inhibitors DIDS (100 micromol/L) and ethylisopropylamiloride or by removal of buffer Na+, indicating that the acute reduction in fluid shear stress activates the extracellular Na+-dependent Cl(-)-HCO3- exchanger and the Na+-H+ exchanger and increases cytosolic pH in vascular endothelial cells.