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      Coexpression of mRNAs for P2X 1, P2X 2 and P2X 4 Receptors in Rat Vascular Smooth Muscle: An in situ Hybridization and RT-PCR Study

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          The expression of mRNAs for three P2X receptor subtypes (PX2<sub>1</sub>, P2X<sub>2</sub>, P2X<sub>4</sub>) in the rat vascular system was studied by in situ hybridization and RT-PCR. In heart sections mRNAs transcripts for all three receptors were colocalized in smooth muscle cells of coronary vessels, while no specific positivity was apparent in myocardium. Coexpression of P2X receptor mRNA transcripts were also observed in other peripheral vessels, including aorta, pulmonary artery, internal and external iliac arteries, renal artery and femoral artery. By contrast, no mRNA transcripts of the above receptors were found in the superior mesenteric artery. RT-PCR performed on microdissected tissues (coronary arteries, aorta and myocardium from various heart areas) confirmed the presence of P2X<sub>1</sub>, P2X<sub>2</sub> and P2X<sub>4</sub> receptor mRNAs. Furthermore, in the same tissues two splice variants of the P2X<sub>2</sub> receptor were identified. These results reveal an important molecular heterogeneity of P2X receptors, thus substantiating the possibility of a heteropolymeric assembly of ATP-gated ion channels in the cardiovascular system.

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          Most cited references 7

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          Coexpression of P2X2 and P2X3 receptor subunits can account for ATP-gated currents in sensory neurons.

          Cation-selective P2X receptor channels were first described in sensory neurons where they are important for primary afferent neurotransmission and nociception. Here we report the cloning of a complementary DNA (P2X3) from rat dorsal root ganglia that had properties dissimilar to those of sensory neurons. We also found RNA for (P2X1)(ref. 7), (P2X2)(ref. 8) and P2X4 (ref. 9) in sensory neurons; channels expressed from individual cDNAs did not reproduce those of sensory ganglia. Coexpression of P2X3 with P2X2, but not other combinations, yielded ATP-activated currents that closely resembled those in sensory neurons. These properties could not be accounted for by addition of the two sets of channels, indicating that a new channel had formed by subunit heteropolymerization. Although in some tissues responses to ATP can be accounted for by homomeric channels, our results indicate that ATP-gated channels of sensory neurons may form by a specific heteropolymerization of P2X receptor subunits.
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            Purinoceptors: Are there families of P2X and P2Y purinoceptors?

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              Differential distribution of two ATP-gated channels (P2X receptors) determined by immunocytochemistry.

              Several P2X receptor subunits were recently cloned; of these, one was cloned from the rat vas deferens (P2X1) and another from pheochromocytoma (PC12) cells differentiated with nerve growth factor (P2X2). Peptides corresponding to the C-terminal portions of the predicted receptor proteins (P2X1 391-399 and P2X2 460-472) were used to generate antisera in rabbits. The specificities of antisera were determined by staining human embryonic kidney cells stably transfected with either P2X1 or P2X2 receptors and by absorption controls with the cognate peptides. In the vas deferens and the ileal submucosa, P2X1 immunoreactivity (ir) was restricted to smooth muscle, whereas P2X2-ir was restricted to neurons and their processes. Chromaffin cells of the adrenal medulla and PC12 cells contained both P2X1- and P2X2-ir. P2X1-ir was also found in smooth muscle cells of the bladder, cardiac myocytes, and nerve fibers and terminals in the superficial dorsal horn of the spinal cord. In contrast, P2X2-ir was observed in scattered cells of the anterior pituitary, neurons in the hypothalamic arcuate and paraventricular nuclei, and catecholaminergic neurons in the olfactory bulb, the substantia nigra, ventral tegmental area, and locus coeruleus. A plexus of nerve fibers and terminals in the nucleus of the solitary tract contained P2X2-ir. This staining disappeared after nodose ganglionectomy, consistent with a presynaptic function. The location of the P2X1 subunit in smooth muscle is consistent with its role as a postjunctional receptor in autonomic transmission, while in neurons, these receptors appear in both postsynaptic and presynaptic locations.

                Author and article information

                J Vasc Res
                Journal of Vascular Research
                S. Karger AG
                June 1998
                09 June 1998
                : 35
                : 3
                : 179-185
                a Department of Anatomy and Developmental Biology, University College London, UK; b Department of Cardiovascular Sciences, University of Rome ‘La Sapienza’, Rome, Italy
                25582 J Vasc Res 1998;35:179–185
                © 1998 S. Karger AG, Basel

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                Page count
                Figures: 6, References: 21, Pages: 7
                Research Paper


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