P2X and P2Y Receptors Mediate Contraction Induced by Electrical Field Stimulation in Feline Esophageal Smooth Muscle

It is well-known that electrical field stimulation (EFS)-induced contraction is mediated by a cholinergic mechanism and other neurotransmitters. NO, ATP, calcitonin gene-related peptide (CGRP), and substance P are released by EFS. To investigate the purinergic mechanism involved in the EFS-induced contraction, purinegic receptors antagonists were used. Suramine, a non-selective P2 receptor antagonist, reduced the contraction induced by EFS. NF023 (10(-7)~10(-4) M), a selective P2X antagonist, inhibited the contraction evoked by EFS. Reactive blue (10(-6)~10(-4) M), selective P2Y antagonist, also blocked the contraction in a dose-dependent manner. In addition, P2X agonist alpha,beta-methylene 5'-adenosine triphosphate (alphabetaMeATP, 10(-7)~10(-5) M) potentiated EFS-induced contraction in a dose-dependent manner. P2Y agonist adenosine 5'-[beta-thio]diphosphate trilithium salt (ADPbetaS, 10(-7)~10(-5) M) also potentiated EFS-induced contractions in a dose-dependent manner. Ecto-ATPase activator apyrase (5 and 10 U/ml) reduced EFS-induced contractions. Inversely, 6-N,N-diethyl-D-beta,gamma-dibromomethylene 5'-triphosphate triammonium (ARL 67156, 10(-4) M) increased EFS-induced contraction. These data suggest that endogenous ATP plays a role in EFS-induced contractions which are mediated through both P2X-receptors and P2Y-receptors stimulation in cat esophageal smooth muscle.

P2 Receptor-mediated Inhibition of Vasopressin-stimulated Fluid Transport and cAMP Responses in AQP2-transfected MDCK Cells

We cultured canine kidney (MDCK) cells stably expressing aquaporin-2 (AQP2) on collagen-coated permeable membrane filters and examined the effect of extracellular ATP on arginine vasopressin (AVP)-stimulated fluid transport and cAMP production. Exposure of cell monolayers to basolateral AVP resulted in stimulation of apical to basolateral net fluid transport driven by osmotic gradient which was formed by addition of 500 mM mannitol to basolateral bathing solution. Pre-exposure of the basolateral surface of cell monolayers to ATP (100 ?M) for 30 min significantly inhibited the AVP-stimulated net fluid transport. In these cells, AVP-stimulated cAMP production was suppressed as well. Profile of the effects of different nucleotides suggested that the P2Y2 receptor is involved in the action of ATP. ATP inhibited the effect of isoproterenol as well, but not that of forskolin to stimulate cAMP production. The inhibitory effect of ATP on AVP-stimulated fluid movement was attenuated by a protein kinase C inhibitor, calphostin C or pertussis toxin. These results suggest that prolonged activation of the P2 receptors inhibits AVP-stimulated fluid transport and cAMP responses in AQP2 transfected MDCK cells. Depressed responsiveness of the adenylyl cyclase by PKC-mediated modification of the pertussis-toxin sensitive Gi protein seems to be the underlyihng mechanism.

Effect of P2 Nucleotide Receptor Activation on Phosphate Transport in Rabbit Proximal Tubular Cells / 대한신장학회잡지

BACKGROUND: Extracellular nucleotides act as agonists to regulate a broad range of physiological processes by interacting with P2 receptors in various tissues including the kidney tubules. This study was undertaken to evaluate the effect of P2 receptor activation on PTH-dependent regulation of phosphate transport in the renal proximal tubular cells. METHODS: Proximal tubular cells were isolated from the rabbit kidney and grown as monolayers on 24 well culture plates. Phosphate uptake was determined by measuring the uptake of radiolabeled phosphate into cell monolayers. Cyclic AMP content was determined by radioimmunoassay using [3H]cAMP assay kit. RESULTS: Activation of P2 receptors with ATP exerted differential effects on phosphate uptake and cAMP generation. In the absence of PTH, it inhibited phosphate uptake and stimulated cAMP generation. In contrast, in the presence of PTH, it attenuated PTH-induced stimulation of cAMP generation and inhibition of phosphate uptake. The profile of the effects of different P2 agonists suggested that P2Y1- and P2Y2-like receptors are involved in the effects of ATP. The effect of ATP to interfere with the PTH-induced regulation was significantly blocked by calphostin C, pertussis toxin or PKC-depletion, whereas, the effects of ATP in the absence of PTH were abolished by indomethacin. CONCLUSION: Our results suggest that PKC-dependent modification of Gi proteins and, subsequently, reduced responsiveness of adenylate cyclases is responsible for the attenuating effect of ATP on the PTH-dependent regulation of phosphate transport in rabbit proximal tubule cells.

Function of P2 receptors in skeletal system and inflammatory disease of bone / 中国药理学通报

Extracellular purine and pyrimidine nucleotides produce the biologic effects involved in activating P2 receptors.P2 receptors are divided P2X and P2Y receptor subtypes.There is molecular and functional evidence for widespread expression of P2X and P2Y receptor subtypes in osteoblasts,osteoclasts and cartilage cells of the skeletal system.Working through P2 receptors,ATP and other nucleotides released into the bone microenvironment regulate formation and activity of bone and cartilage,including development,growth,turnover and repair of biological functions.The release of nucleotides is increased under inflammatory conditions,and localized ATP release could stimulate formation and activation of osteoclasts.Abnormalities of bone remodelling can produce a variety of skeletal disorders.P2 receptors play an important role in the inflammatory disease of bone.