Dual signaling pathways of arterial constriction by extracellular uridine 5'-triphosphate in the rat

Extracellular Uridine Nucleotides-Induced Contractions Were Increased in Femoral Arteries of Spontaneously Hypertensive Rats

INTRODUCTION

Femoral arterial dysfunction including abnormal vascular responsiveness to endogenous ligands was often seen in arterial hypertension. Extracellular nucleotides including uridine 5'-diphosphate (UDP) and uridine 5'-triphosphate (UTP) play important roles for homeostasis in the vascular system including controlling the vascular tone. However, responsiveness to UDP and UTP in femoral arteries under arterial hypertension remains unclear. The aim of this study was to investigate if hypertension has an effect of vasoconstrictive responsiveness to UDP and UTP in femoral arteries of spontaneously hypertensive rats (SHRs) and Wistar-Kyoto rats (WKYs) after 7 and 12 months old.

METHODS

Organ baths were conducted to determine vascular reactivity in isolated femoral arterial rings.

RESULTS

In femoral arteries obtained from 12-month-old rats, augmented contractile responses to UDP and UTP were seen in femoral arteries of SHR than in those of WKY under situations not only intact but also nitric oxide synthase inhibition, whereas no difference of extracellular potassium-induced vasocontraction was seen in both SHR and WKY groups. Similar contraction trends occurred in femoral arteries obtained from 7-month-old rats. Moreover, contractions induced by UDP and UTP were increased in endothelium-denuded arteries. Cyclooxygenase inhibition decreased the contractions induced by these nucleotides and abolished the differences in responses between the SHR and WKY groups.

CONCLUSIONS

This study demonstrates the importance of regulation of extracellular uridine nucleotides-induced contractions in hypertension-associated peripheral arterial diseases.

Comparison of mRNA Expression of P2X Receptor Subtypes in Different Arterial Tissues of Rats

This study aims to compare the expression of P2X receptor subtype mRNA in different arterial tissues of rats. After the rats were sacrificed, the internal carotid, pulmonary, thoracic aorta, mesenteric and caudal arteries were dissected out. Then, the P2X receptor mRNA expression in different blood vessels was detected by reverse transcription-polymerase chain reaction (RT-PCR) and real-time quantitative polymerase chain reaction. The P2X1, P2X4 and P2X7 receptor mRNA amplification products revealed specific bands of the same size as the amplified target fragment in their respective lanes, while the P2X2, P2X3, P2X5 and P2X6 receptor mRNA amplification products did not reveal significant specific bands in their respective lanes by RT-PCR. Based on the P2X1 receptor mRNA expression of the mesenteric artery, there were no significant differences in the internal carotid, pulmonary and thoracic aorta (0.64 ± 0.07, 0.17 ± 0.11 and 1.49 ± 0.65, respectively). However, the P2X1 receptor mRNA expression level in the caudal artery significantly increased (11.06 ± 1.99, P < 0.01). Furthermore, there was no difference in P2X4 receptor mRNA expression among these five blood vessels (P > 0.05). The P2X7 receptor mRNA expression level was significantly different: pulmonary artery < tail artery = thoracic aorta < internal carotid artery < mesenteric artery. The relative P2X1 receptor mRNA expression in the caudal artery was observed to be elevated when compared to that of the internal carotid, pulmonary and thoracic aorta as well as the mesenteric arteries. The P2X7 receptor mRNA expression level is pulmonary artery < caudal artery = thoracic aorta < internal carotid artery < mesenteric artery. P2X4 receptor mRNA expression was not significantly different among these five blood vessels.

Ca2+ dependent but PKC independent signalling mediates UTP induced contraction of rat mesenteric arteries

Uridine triphosphate (UTP) can be released from damaged cells to cause vasoconstriction. Although UTP is known to act through P2Y receptors and PLC activation in vascular smooth muscle, the role of PKC in generating the response is somewhat unclear. Here we have used Tat-linked membrane permeable peptide inhibitors of PKC to assess the general role of PKC and also of specific isoforms of PKC in the UTP induced contraction of rat mesenteric artery. We examined the effect of PKC inhibition on UTP induced contraction, increased cytoplasmic Ca²⁺ and reduction of K⁺ currents and found that PKC inhibition caused a relatively small attenuation of contraction but had little effect on changes in cytoplasmic Ca²⁺. UTP attenuation of both voltage-gated (K_v) and ATP-dependent (K_ATP) K⁺ currents was abolished when intracellular Ca²⁺ was decreased from 100 to 20 nM. PKC inhibition reduced slightly the ability of UTP to attenuate K_v currents but had no effect on K_ATP current inhibition. In conclusion, both UTP induced contraction of mesenteric artery and the inhibition of K_v and K_ATP currents of mesenteric artery smooth muscle cells by UTP are relatively independent of PKC activation; furthermore, the inhibition of both K_v and K_ATP currents requires intracellular Ca²⁺.

Surface vacuolar ATPase in ameloblastoma contributes to tumor invasion of the jaw bone

Ameloblastoma is the most common benign odontogenic tumor in Japan. It is believed that it expands in the jaw bone through peritumoral activation of osteoclasts by receptor activator of nuclear factor kappa-B ligand (RANKL) released from the ameloblastoma, as in bone metastases of cancer cells. However, the clinical features of ameloblastoma, including its growth rate and patterns of invasion, are quite different from those of bone metastasis of cancer cells, suggesting that different underlying mechanisms are involved. Therefore, in the present study, we examined the possible mechanisms underlying the invasive expansion of ameloblastoma in the jaw bone. Expression levels of RANKL assessed by western blotting were markedly lower in ameloblastoma (AM-1) cells than in highly metastatic oral squamous cell carcinoma (HSC-3) cells. Experiments coculturing mouse macrophages (RAW264.7) with AM-1 demonstrated low osteoclastogenic activity, as assessed by tartrate-resistant acid phosphatase (TRAP)-positive multinuclear cell formation, probably because of low release of RANKL, whereas cocultures of RAW264.7 with HSC-3 cells exhibited very high osteoclastogenic activity. Thus, RANKL release from AM-1 appeared to be too low to generate osteoclasts. However, AM-1 cultured directly on calcium phosphate-coated plates formed resorption pits, and this was inhibited by application of bafilomycin A1. Furthermore, vacuolar-type H+-ATPase (V-ATPase) and H+/Cl- exchange transporter 7 (CLC-7) were detected on the surface of AM-1 cells by plasma membrane biotinylation and immunofluorescence analysis. Immunohistochemical analysis of clinical samples of ameloblastoma also showed plasma membrane-localized V-ATPase and CLC-7 in the epithelium of plexiform, follicular and basal cell types. The demineralization activity of AM-1 was only 1.7% of osteoclasts demineralization activity, and the growth rate was 20% of human normal skin keratinocytes and HSC-3 cells. These results suggest that the slow expansion of several typical types of ameloblastomas in jaw bone is attributable to its slow growth and low demineralization ability.

Pharmacological characterization of uracil nucleotide-preferring P2Y receptors modulating intestinal motility: a study on mouse ileum

We investigated the possible modulation of the intestinal contractility by uracil nucleotides (UTP and UDP), using as model the murine small intestine. Contractile activity of a mouse ileum longitudinal muscle was examined in vitro as changes in isometric tension. Transcripts encoding for uracil-sensitive receptors was investigated by RT-PCR. UDP induced muscular contractions, sensitive to PPADS, suramin, or MRS 2578, P2Y(6) receptor antagonist, and mimicked by PSB 0474, P2Y(6)-receptor agonist. UTP induced biphasic effects characterized by an early inhibition of the spontaneous contractile activity followed by muscular contraction. UTP excitatory effects were antagonized by PPADS, suramin, but not by MRS 2578, whilst the inhibitory effects were antagonized by PPADS but not by suramin or MRS 2578. UTPγS, P2Y(2)/(4) receptor agonist but not 2-thio-UTP, P2Y(2) receptor agonist, mimicked UTP effects. The inhibitory effects induced by UTP was abolished by ATP desensitization and increased by extracellular acidification. UDP or UTP responses were insensitive to TTX, atropine, or L-NAME antagonized by U-73122, inhibitor of phospholipase C (PLC) and preserved in the presence of nifedipine or low Ca(2+) solution. Transcripts encoding the uracil nucleotide-preferring receptors were expressed in mouse ileum. Functional postjunctional uracil-sensitive receptors are present in the longitudinal muscle of the mouse ileum. Activation of P2Y(6) receptors induces muscular contraction, whilst activation of P2Y(4) receptors leads to inhibition of the contractile activity. Indeed, the presence of atypical UTP-sensitive receptors leading to muscular contraction is suggested. All uracil-sensitive receptors are linked to the PLC pathway.

Potentiation of regulatory volume decrease by a p2-like receptor and arachidonic acid in american alligator erythrocytes

This study examined the role of a P2 receptor and arachidonic acid (AA) in regulatory volume decrease (RVD) by American alligator red blood cells (RBCs). Osmotic fragility was determined optically, mean cell volume was measured by electronic sizing, and changes in intracellular Ca(2+) concentration were visualized using fluorescence microscopy. Gadolinium (50 μM), hexokinase (2.5 U/ml), and suramin (100 μM) increased osmotic fragility, blocked volume recovery after hypotonic shock, and prevented a rise in intracellular Ca(2+) that normally occurs during cell swelling. The P2X antagonists PPADS (50 μM) and TNP-ATP (10 μM) also increased fragility and inhibited volume recovery. In contrast, ATPγS (10 μM), α,β-methylene-ATP (50 μM) and Bz-ATP (50 μM) had the opposite effect, whereas 2-methylthio-ATP (50 μM) and UTP (10 μM) had no effect. In addition, the phospholipase A(2) (PLA(2)) inhibitors ONO-RS-082 (10 μM), chlorpromazine (10 μM), and isotetrandrine (10 μM) increased osmotic fragility and blocked volume recovery, whereas AA (10 μM) and its nonhydrolyzable analog eicosatetraynoic acid (ETYA, 10 μM) had the reverse effect. Further, AA (10 μM), but not ATPγS (10 μM), prevented the inhibitory effect of a low Ca(2+)-EGTA Ringer on RVD, whereas both AA (10 μM) and ATPγS (10 μM) caused cell shrinkage under isosmotic conditions. In conclusion, our results are consistent with the presence of a P2-like receptor whose activation stimulated RVD. In addition, AA also was important for volume recovery.