scholarly journals PC-PLC/sphingomyelin synthase activity plays a central role in the development of myogenic tone in murine resistance arteries

2015 ◽  
Vol 308 (12) ◽  
pp. H1517-H1524 ◽  
Author(s):  
Joseph R. H. Mauban ◽  
Joseph Zacharia ◽  
Seth Fairfax ◽  
Withrow Gil Wier
Keyword(s):  
Specific Inhibitor ◽  
Intrinsic Property ◽  
Tissue Perfusion ◽  
Pressure Control ◽  
Mesenteric Arteries ◽  
Myogenic Tone ◽  
Resistance Arteries ◽  
Virtual Absence ◽  
Sphingomyelin Synthase

Myogenic tone is an intrinsic property of the vasculature that contributes to blood pressure control and tissue perfusion. Earlier investigations assigned a key role in myogenic tone to phospholipase C (PLC) and its products, inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). Here, we used the PLC inhibitor, U-73122, and two other, specific inhibitors of PLC subtypes (PI-PLC and PC-PLC) to delineate the role of PLC in myogenic tone of pressurized murine mesenteric arteries. U-73122 inhibited depolarization-induced contractions (high external K+ concentration), thus confirming reports of nonspecific actions of U-73122 and its limited utility for studies of myogenic tone. Edelfosine, a specific inhibitor of PI-PLC, did not affect depolarization-induced contractions but modulated myogenic tone. Because PI-PLC produces IP3, we investigated the effect of blocking IP3 receptor-mediated Ca2+ release on myogenic tone. Incubation of arteries with xestospongin C did not affect tone, consistent with the virtual absence of Ca2+ waves in arteries with myogenic tone. D-609, an inhibitor of PC-PLC and sphingomyelin synthase, strongly inhibited myogenic tone and had no effect on depolarization-induced contraction. D-609 appeared to act by lowering cytoplasmic Ca2+ concentration to levels below those that activate contraction. Importantly, incubation of pressurized arteries with a membrane-permeable analog of DAG induced vasoconstriction. The results therefore mandate a reexamination of the signaling pathways activated by the Bayliss mechanism. Our results suggest that PI-PLC and IP3 are not required in maintaining myogenic tone, but DAG, produced by PC-PLC and/or SM synthase, is likely through multiple mechanisms to increase Ca2+ entry and promote vasoconstriction.

Role of T-type calcium channels in myogenic tone of skeletal muscle resistance arteries

2002 ◽  
Vol 283 (6) ◽  
pp. H2239-H2243 ◽  
Author(s):  
Ed VanBavel ◽  
Oana Sorop ◽  
Ditte Andreasen ◽  
Martin Pfaffendorf ◽  
Boye L. Jensen
Keyword(s):  
Calcium Channels ◽  
Southern Blotting ◽  
Myogenic Tone ◽  
Cremaster Muscle ◽  
Resistance Arteries ◽  
Rt Pcr ◽  
Response Curves ◽  
Potent Effect ◽  
Channel Expression

T-type calcium channels may be involved in the maintenance of myogenic tone. We tested their role in isolated rat cremaster arterioles obtained after CO2anesthesia and decapitation. Total RNA was analyzed by RT-PCR and Southern blotting for calcium channel expression. We observed expression of voltage-operated calcium (CaV) channels CaV3.1 (T-type), CaV3.2 (T-type), and CaV1.2 (L-type) in cremaster arterioles ( n= 3 rats). Amplification products were observed only in the presence of reverse transcriptase and cDNA. Concentration-response curves of the relatively specific L-type blocker verapamil and the relatively specific T-type blockers mibefradil and nickel were made on cannulated vessels with either myogenic tone (75 mmHg) or a similar level of constriction induced by 30 mM K+ at 35 mmHg. Mibefradil and nickel were, respectively, 162-fold and 300-fold more potent in inhibiting myogenic tone compared with K+-induced constriction [log(IC50, M): mibefradil, basal −7.3 ± 0.2 ( n = 9) and K+ −5.1 ± 0.1 ( n = 5); nickel, basal −4.1 ± 0.2 ( n = 5) and K+ −1.6 ± 0.5 ( n = 5); means ± SE]. Verapamil had a 17-fold more potent effect [log(IC50, M): basal −6.6 ± 0.1 ( n = 5); K+ −5.4 ± 0.3 ( n = 4); all log(IC50) P < 0.05, basal vs. K+]. These data suggest that T-type calcium channels are expressed and involved in maintenance of myogenic tone in rat cremaster muscle arterioles.

Renal vascular dysfunction precedes the development of renal damage in the hypertensive Fawn-Hooded rat

2010 ◽  
Vol 298 (3) ◽  
pp. F625-F633 ◽  
Author(s):  
Peter Ochodnický ◽  
Robert H. Henning ◽  
Hendrik J. Buikema ◽  
Dick de Zeeuw ◽  
Abraham P. Provoost ◽  
...  
Keyword(s):  
Renal Damage ◽  
Vascular Dysfunction ◽  
Organ Damage ◽  
Mesenteric Arteries ◽  
Myogenic Tone ◽  
Myogenic Response ◽  
Resistance Arteries ◽  
Renal Vasculature ◽  
End Organ Damage ◽  
Renal Vascular

It is unknown whether generalized vascular dysfunction precedes the development of kidney disease. Therefore, we studied myogenic constriction and endothelium-mediated dilatory responses in two inbred Fawn-Hooded (FH) rat strains, one of which spontaneously develops hypertension, proteinuria, and glomerulosclerosis (FHH), whereas the other (FHL) does not. Small renal, mesenteric resistance arteries and thoracic aorta isolated from FH rats before (7 wk old) and after the development of mild proteinuria (12 wks old) were mounted in perfused and isometric set-ups, respectively. Myogenic response, endothelium-dependent relaxation, and the contribution of endothelium-mediated dilatory compounds were studied using their respective inhibitors. Myogenic reactivity was assessed constructing pressure-diameter curves in the presence and absence of calcium. At the age of 7 wk, renal arteries isolated from kidneys of FHH rats developed significantly lower myogenic tone compared with FHL, most likely because of excessive cyclo-oxygenase 1-mediated production of constrictive prostaglandins. Consequently, young FHH demonstrated reduced maximal myogenic tone (22 ± 4.8 vs. 10.8 ± 2.0%, P = 0.03) and the peak myogenic index (−6.9 ± 4.8 vs. 0.6 ± 0.8%/mmHg, P = 0.07 for FHL vs. FHH, respectively). Active myogenic curves obtained in mesenteric arteries isolated from 7-wk-old rats did not differ between either strain, demonstrating a similar level of systemic myogenic tone in FHL and FHH rats. Therefore, before any renal end-organ damage is present, myogenic response seems selectively impaired in renal vasculature of FHH rats. Aortic reactivity did not differ between FHL and FHH at the time points studied. The present study shows that vascular dysfunction in both small renal and systemic arteries precedes renal end-organ damage in a spontaneous model of hypertension-associated renal damage. These early vascular changes might be potentially involved in the increased susceptibility of FHH rats to renal injury.

Role of Endothelium in the Action of Isoflurane on Vascular Smooth Muscle of Isolated Mesenteric Resistance Arteries

2001 ◽  
Vol 95 (4) ◽  
pp. 990-998 ◽  
Author(s):  
Kaoru Izumi ◽  
Takashi Akata ◽  
Shosuke Takahashi
Keyword(s):  
Contractile Response ◽  
Isometric Force ◽  
Direct Action ◽  
Control Level ◽  
Mesenteric Arteries ◽  
Systemic Resistance ◽  
Resistance Arteries ◽  
Mesenteric Resistance Artery

Background It is believed that isoflurane decreases blood pressure predominantly by decreasing systemic vascular resistance with modest myocardial depression. Nevertheless, little information is available regarding the direct action of isoflurane on systemic resistance arteries. Methods With use of the isometric force recording method, the action of isoflurane on contractile response to norepinephrine, a neurotransmitter that plays a central role in sympathetic maintenance of vascular tone in vivo, was investigated in isolated rat small mesenteric arteries. Results In the endothelium-intact strips, the norepinephrine response was initially enhanced after application of isoflurane (2-5%), but it was subsequently almost normalized to the control level during exposure to isoflurane. However, the norepinephrine response was notably inhibited after washout of isoflurane. In the endothelium-denuded strips, the norepinephrine response was gradually inhibited during exposure to isoflurane (&gt; or = 3%), and the inhibition was prolonged after wash-out of isoflurane. The isoflurane-induced enhancement of norepinephrine response was still observed after inhibitions of the nitric oxide, endothelium-derived hyperpolarizing factor, cyclooxygenase and lipoxygenase pathways, or after blockade of endothelin-1, angiotensin-II, and serotonin receptors; however, it was prevented by superoxide dismutase. Conclusions In isolated mesenteric resistance artery, the action of isoflurane on contractile response to norepinephrine consists of two distinct components: an endothelium-dependent enhancing component and an endothelium-independent inhibitory component. During exposure to isoflurane, the former counteracted the latter, preventing the norepinephrine response from being strongly inhibited. However, only the endothelium-independent component persists after washout of isoflurane, causing prolonged inhibition of the norepinephrine response. Superoxide anions may be involved in the enhanced response to norepinephrine.

Role of CO in attenuated vasoconstrictor reactivity of mesenteric resistance arteries after chronic hypoxia

2002 ◽  
Vol 282 (1) ◽  
pp. H30-H37 ◽  
Author(s):  
Rayna J. Gonzales ◽  
Benjimen R. Walker
Keyword(s):  
Chronic Hypoxia ◽  
Protoporphyrin Ix ◽  
Aortic Ring ◽  
Mesenteric Arteries ◽  
Zinc Protoporphyrin ◽  
Sprague Dawley ◽  
Resistance Arteries ◽  
Sprague Dawley Rats ◽  
Oxide Synthase

Chronic hypoxia (CH) is associated with a persistent reduction in systemic vasoconstrictor reactivity. Experiments on aortic ring segments isolated from CH rats suggest that enhanced vascular expression of heme oxygenase (HO) and resultant production of the vasodilator carbon monoxide (CO) may underlie this attenuated vasoreactivity after hypoxia. Similar to the aorta, small arteries from CH rats exhibit blunted reactivity; however, the regulatory role of CO in the resistance vasculature has not been established. Therefore, we examined the significance of HO activity on responsiveness to phenylephrine (PE) in the mesenteric circulation of control and CH rats. To document that the mesenteric bed demonstrates reduced reactivity after CH, we determined the vasoconstrictor responses of conscious, chronically instrumented male Sprague-Dawley rats to PE under control conditions and then immediately after exposure to 48 h CH (0.5 atm). All rats showed reduced mesenteric vasoconstriction to PE after CH. To examine the role of CO in reduced reactivity, small mesenteric arteries (100–200 μm intraluminal diameter) from control and 48-h CH rats were isolated and mounted on glass cannulas, pressurized to 60 mmHg and superfused with increasing concentrations of PE under normoxic conditions. Similar to the intact circulation, vessels from CH rats exhibited reduced vasoconstrictor sensitivity to PE compared with controls that persisted in the presence of nitric oxide synthase inhibition. The HO inhibitor, zinc protoporphyrin IX (5 μM) enhanced reactivity only in CH vessels. Additionally, a range of concentrations of the HO substrate heme-l-lysinate caused vasodilation in CH vessels but not in controls. Thus we conclude that CO contributes a significant vasodilator influence in resistance vessels after CH that may account for diminished vasoconstrictor responsiveness under these conditions.

scholarly journals Advanced age decreases local calcium signaling in endothelium of mouse mesenteric arteries in vivo

2016 ◽  
Vol 310 (9) ◽  
pp. H1091-H1096 ◽  
Author(s):  
Erika M. Boerman ◽  
Jesse E. Everhart ◽  
Steven S. Segal
Keyword(s):  
Calcium Signaling ◽  
Fluorescent Protein ◽  
Vascular Dysfunction ◽  
Tissue Perfusion ◽  
Mesenteric Arteries ◽  
Advanced Age ◽  
Resistance Arteries ◽  
Internal Elastic Lamina ◽  
Effects Of Aging

Aging is associated with vascular dysfunction that impairs tissue perfusion, physical activity, and the quality of life. Calcium signaling in endothelial cells (ECs) is integral to vasomotor control, exemplified by localized Ca2+ signals within EC projections through holes in the internal elastic lamina (IEL). Within these microdomains, endothelium-derived hyperpolarization is integral to smooth muscle cell (SMC) relaxation via coupling through myoendothelial gap junctions. However, the effects of aging on local EC Ca2+ signals (and thereby signaling between ECs and SMCs) remain unclear, and these events have not been investigated in vivo. Furthermore, it is unknown whether aging affects either the number or the size of IEL holes. In the present study, we tested the hypothesis that local EC Ca2+ signaling is impaired with advanced age along with a reduction in IEL holes. In anesthetized mice expressing a Ca2+-sensitive fluorescent protein (GCaMP2) selectively in ECs, our findings illustrate that for mesenteric arteries controlling splanchnic blood flow the frequency of spontaneous local Ca2+ signals in ECs was reduced by ∼85% in old (24–26 mo) vs. young (3–6 mo) animals. At the same time, the number (and total area) of holes per square millimeter of IEL was reduced by ∼40%. We suggest that diminished signaling between ECs and SMCs contributes to dysfunction of resistance arteries with advanced age. Listen to this article's corresponding podcast at http://ajpheart.podbean.com/e/aging-impairs-endothelial-ca2-signaling/ .

scholarly journals Estrogen replacement enhances EDHF-mediated vasodilation of mesenteric and uterine resistance arteries: role of endothelial cell Ca2+

2009 ◽  
Vol 296 (3) ◽  
pp. E503-E512 ◽  
Author(s):  
Natalie Z. Burger ◽  
Olga Y. Kuzina ◽  
George Osol ◽  
Natalia I. Gokina
Keyword(s):  
Endothelial Cell ◽  
Underlying Mechanism ◽  
Mature Female ◽  
Mesenteric Arteries ◽  
Female Rats ◽  
Estrogen Replacement ◽  
Resistance Arteries ◽  
Uterine Arteries ◽  
Small Resistance

Endothelium-derived hyperpolarizing factor (EDHF) plays an important role in the regulation of vascular microcirculatory tone. This study explores the role of estrogen in controlling EDHF-mediated vasodilation of uterine resistance arteries of the rat and also analyzes the contribution of endothelial cell (EC) Ca2+ signaling to this process. A parallel study was also performed with mesenteric arteries to provide comparison with a nonreproductive vasculature. Mature female rats underwent ovariectomy, with one half receiving 17β-estradiol replacement (OVX+E) and the other half serving as estrogen-deficient controls (OVX). Uterine or mesenteric resistance arteries were harvested, cannulated, and pressurized. Nitric oxide and prostacyclin production were inhibited with 200 μM NG-nitro-l-arginine and 10 μM indomethacin, respectively. ACh effectively dilated the arteries preconstricted with phenylephrine but failed to induce dilation of vessels preconstricted with high-K+ solution. ACh EC50 values were decreased by estrogen replacement by five- and twofold in uterine and mesenteric arteries, respectively. As evidenced by fura-2-based measurements of EC cytoplasmic Ca2+ concentration ([Ca2+]i), estrogen replacement was associated with increased basal and ACh-stimulated EC [Ca2+]i rise in uterine, but not mesenteric, vessels. These data demonstrate that EDHF contributes to endothelium-dependent vasodilation of uterine and mesenteric resistance arteries and that estrogen controls EDHF-related mechanism(s) more efficiently in reproductive vs. nonreproductive vessels. Enhanced endothelial Ca2+ signaling may be an important underlying mechanism in estrogenic modulation of EDHF-mediated vasodilation in small resistance uterine arteries.

Abstract 138: Altered Vascular Reactivity in Mice Overexpressing Adipocyte Mineralocorticoid Receptors - Role of Rho Kinase.

Hypertension ◽  
2012 ◽  
Vol 60 (suppl_1) ◽  
Author(s):  
Aurelie Nguyen Dinh Cat ◽  
Tayze T Antunes ◽  
Glaucia E Callera ◽  
Augusto C Montezano ◽  
Ying He ◽  
...  
Keyword(s):  
Adipose Tissue ◽  
Vascular Function ◽  
Vascular Reactivity ◽  
Molecular Mechanisms ◽  
Rho Kinase ◽  
Mesenteric Arteries ◽  
Mineralocorticoid Receptors ◽  
Resistance Arteries ◽  
Brown Adipose

Aldosterone (aldo) plays a role in cardiovascular diseases, including hypertension and obesity. We previously demonstrated that adipocyte-derived factors regulate vascular function and cell signaling in cultured vascular smooth muscle cells. Moreover, adipocytes are able to produce aldo, which influences vascular reactivity. Plasma levels of aldo are positively correlated with obesity and hypertension. However, the pathophysiological role of aldo and mineralocorticoid receptors (MR) in adipose tissue and its interactions with the vasculature remains elusive. In our study, we investigated molecular mechanisms whereby activation of MR, in adipocytes, leads to release of vascular reactive factors and regulation of vascular tone, using a conditional transgenic mouse model that overexpresses MR only in the adipocytes. Vascular reactivity of resistance mesenteric arteries to acetylcholine (Ach), sodium nitroprusside and phenylephrine (Phe), in the absence or presence of fat conditioned medium (Fcm) from control and adipocyte overexpressing MR (DT) mice, was performed by myography. In basal conditions, endothelial dysfunction was not observed in DT or control mice. However, in the presence of Fcm from DT mice, relaxation to Ach was impaired in control mice (Ach 10 -6 M: 77.5±9.6% no Fcm vs. 49.8±7.5% Fcm, p<0.05), an effect blocked by N-acetyl-cysteine (anti-oxidant) (Ach 10 -6 M: 82.2±6.6%). Resistance arteries from DT mice had decreased Phe-induced contraction, compared to control mice (Phe 10 -5 M: 2.7±0.2 mN/mm CT vs. 1.7±0.2 mN/mm DT, p<0.05). Phosphorylation of ezrin, a marker of Rho kinase activation, measured by immunoblotting, was decreased in white and brown adipose tissues of DT (CT: 3.1±0.7 vs. DT: 0.6±0.1, arbitrary units, p<0.05). In conclusion, MR in adipocytes may play an important role in the regulation of vascular function, and may be involved in vascular oxidative stress. MR in adipocytes is also important to the anti-contractile properties of the adipose tissue through downregulation of Rho kinase signaling. Our study identiy novel mechanisms linking vascular and adipose biology through adipocyte MRs.

scholarly journals Role of arachidonic acid lipoxygenase metabolites in acetylcholine-induced relaxations of mouse arteries

2011 ◽  
Vol 300 (3) ◽  
pp. H725-H735 ◽  
Author(s):  
Kathryn M. Gauthier ◽  
Daniel H. Goldman ◽  
Nitin T. Aggarwal ◽  
Yuttana Chawengsub ◽  
J. R. Falck ◽  
...  
Keyword(s):  
Arachidonic Acid ◽  
Abdominal Aorta ◽  
Nordihydroguaiaretic Acid ◽  
Immunoblot Analysis ◽  
Mesenteric Arteries ◽  
Epoxyeicosatrienoic Acid ◽  
Resistance Arteries ◽  
Cox Inhibitor ◽  
Synthase Inhibitor

Arachidonic acid (AA) metabolites function as EDHFs in arteries of many species. They mediate cyclooxygenase (COX)- and nitric oxide (NO)-independent relaxations to acetylcholine (ACh). However, the role of AA metabolites as relaxing factors in mouse arteries remains incompletely defined. ACh caused concentration-dependent relaxations of the mouse thoracic and abdominal aorta and carotid, femoral, and mesentery arteries (maximal relaxation: 57 ± 4%, 72 ± 4%, 82 ± 3%, 80 ± 3%, and 85 ± 3%, respectively). The NO synthase inhibitor nitro-l-arginine (l-NA; 30 μM) blocked relaxations in the thoracic aorta, and l-NA plus the COX inhibitor indomethacin (10 μM) inhibited relaxations in the abdominal aorta and carotid, femoral, and mesenteric arteries (maximal relaxation: 31 ± 10%, 33 ± 5%, 41 ± 8%, and 73 ± 3%, respectively). In mesenteric arteries, NO- and COX-independent relaxations to ACh were inhibited by the lipoxygenase (LO) inhibitors nordihydroguaiaretic acid (NDGA; 10 μM) and BW-755C (200 μM), the K+ channel inhibitor apamin (1 μM), and 60 mM KCl and eliminated by endothelium removal. They were not altered by the cytochrome P-450 inhibitor N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (20 μM) or the epoxyeicosatrienoic acid antagonist 14,15-epoxyeicosa-5( Z)-enoic acid (10 μM). AA relaxations were attenuated by NDGA or apamin and eliminated by 60 mM KCl. Reverse-phase HPLC analysis revealed arterial [14C]AA metabolites that comigrated with prostaglandins, trihydroxyeicosatrienoic acids (THETAs), hydroxyepoxyeicosatrienoic acids (HEETAs), and hydroxyeicosatetraenoic acids (HETEs). Epoxyeicosatrienoic acids were not observed. Mass spectrometry confirmed the identity of 6-keto-PGF1α, PGE2, 12-HETE, 15-HETE, HEETAs, 11,12,15-THETA, and 11,14,15-THETA. AA metabolism was blocked by NDGA and endothelium removal. 11( R),12( S),15( S)-THETA relaxations (maximal relaxation: 73 ± 3%) were endothelium independent and blocked by 60 mM KCl. Western immunoblot analysis and RT-PCR of the aorta and mesenteric arteries demonstrated protein and mRNA expression of leukocyte-type 12/15-LO. Thus, in mouse resistance arteries, 12/15-LO AA metabolites mediate endothelium-dependent relaxations to ACh and AA.

scholarly journals Glycemic control prevents microvascular remodeling and increased tone in Type 2 diabetes: link to endothelin-1

2009 ◽  
Vol 296 (4) ◽  
pp. R952-R959 ◽  
Author(s):  
Kamakshi Sachidanandam ◽  
Jim R. Hutchinson ◽  
Mostafa M. Elgebaly ◽  
Erin M. Mezzetti ◽  
Anne M. Dorrance ◽  
...  
Keyword(s):  
Type 2 Diabetes ◽  
Glycemic Control ◽  
Receptor Expression ◽  
Myogenic Tone ◽  
Resistance Arteries ◽  
Gk Rats ◽  
Endothelin 1 ◽  
Vascular Compliance

Medial thickening and vascular hypertrophy of resistance arteries can lead to cardiovascular complications associated with diabetes. While previous studies have established a role of Type 1 diabetes in vascular remodeling, we recently extended these observations to Type 2 diabetes and reported increased collagen deposition due to alterations in matrix metalloproteinase expression and activity in mesenteric resistance arteries. These studies also showed that remodeling response was mediated by endothelin-1 (ET-1) via activation of ETA receptors, whereas blockade of ETB receptors exacerbated the remodeling. However, the effectiveness of glycemic control strategies in preventing these vascular changes, including activation of the ET system still remained unclear. Also, very little is known about whether and to what extent reorganization of the extracellular matrix (ECM) affects vascular compliance and vasomotor tone. Accordingly, this study assessed structural remodeling of mesenteric microvessels, vascular compliance, and myogenic tone, as well as the role of matrix metalloproteinases (MMP) in mediating these processes. Spontaneously diabetic, non-obese Goto-Kakizaki (GK) rats, a model for Type 2 diabetes, and normoglycemic Wistar rats were used for the studies. A subset of GK rats were administered metformin to achieve euglycemia. Glycemic control normalized the increased media-to-lumen ratios (M/L) and myogenic tone seen in diabetes, as well as normalizing plasma ET-1 levels and mesenteric ETA receptor expression. There was increased collagen synthesis in diabetes paralleled by decreased collagenase MMP-13 activity, while glycemic control attenuated the process. These findings and our previous study taken together suggest that hyperglycemia-mediated activation of ET-1 and ETA receptors alter vascular structure and mechanics in Type 2 diabetes.

scholarly journals Purinergic Receptors Regulate Myogenic Tone in Cerebral Parenchymal Arterioles

2012 ◽  
Vol 33 (2) ◽  
pp. 293-299 ◽  
Author(s):  
Joseph E Brayden ◽  
Yao Li ◽  
Matthew J Tavares
Keyword(s):  
Tissue Perfusion ◽  
P2y Receptors ◽  
Fundamental Aspect ◽  
Myogenic Tone ◽  
Resistance Arteries ◽  
Receptor Isoforms ◽  
Voltage Dependent ◽  
Voltage Dependent Calcium Channels ◽  
The Brain ◽  
Intravascular Pressure

Myogenic tone is a fundamental aspect of vascular behavior in resistance arteries. This contractile response to changes in intravascular pressure is critically involved in blood flow autoregulation in tissues such as the brain, kidneys, and heart. Myogenic tone also helps regulate precapillary pressure and provides a level of background tone upon which vasodilator stimuli act to increase tissue perfusion when appropriate. Despite the importance of these processes in the brain, little is known about the mechanisms involved in control of myogenic tone in the cerebral microcirculation. Here, we report that pharmacological inhibition of P2Y4 and P2Y6 pyrimidine receptors nearly abolished myogenic tone in cerebral parenchymal arterioles (PAs). Molecular suppression of either P2Y4 or P2Y6 receptors using antisense oligodeoxynucleotides reduced myogenic tone by 44% ± 8% and 45% ± 7%, respectively. These results indicate that both receptor isoforms are activated by increased intravascular pressure, which enhances the activity of voltage-dependent calcium channels and increases myogenic tone in PAs. Enhancement or inhibition of ectonucleotidase activity had no effect on parenchymal arteriolar myogenic tone, indicating that this response is not mediated by local release of nucleotides, but rather may involve direct mechanical activation of P2Y receptors in the smooth muscle cells.

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