A growing body of evidence indicates that extracellular ATP released or leaked from nonexcitable cells as well as neurons plays important roles in the regulation of neuronal and glial functions in the entire body through ATP receptors. ATP receptors (ionotropic P2X and metabotropic P2Y receptors) are the most abundant receptor families in living organisms. In the central nervous system, these receptors participate in the synaptic transmission and intercellular communications between neurons and glia. The glia cells are classified into three types: astrocytes; oligodendrocytes; and microglia. There are many reports that spinal microglia express ATP receptors (P2X4, P2X7, P2Y6, and P2Y12 receptors) that have very important roles. We reported that several molecules of microglia are activated after peripheral nerve injury in a neuropathic pain model. In particular, P2X4 receptors (P2X4Rs) expressed in microglia play a critical role in evoking neuropathic pain. P2X4Rs are upregulated in spinal microglia after nerve injury by several factors such as the CC chemokine receptor CCR2, fibronectin in the spinal cord, interferon regulatory factor (IRF) 8, and IRF5 expressed in microglia. The inhibition of P2X4R action suppresses the functions of microglia and neuropathic pain. These results indicate that overexpressing P2X4Rs on microglia are a central player in evoking neuropathic pain.

OBJECTIVE: We examined the effect of race-effort cycling exercise with and without heat stress on post-exercise perceptions of fatigue and pain, as well as mRNA expression in genes related to exercise responses.
METHODS: Trained cyclists (n = 20) completed 40 km time trials during temperate (TC, 21 °C) and hot (HC, 35 °C) conditions. Blood lactates were measured 1 and 5 min post-exercise. Venous blood samples and ratings of fatigue and pain perceptions were obtained at baseline and at 0.5, 8, 24, and 48 h post-exercise. Leukocyte mRNA expression was performed for metabolite detecting, adrenergic, monoamine, and immune receptors using qPCR.
RESULTS: Significantly lower mean power (157 ± 32.3 vs 187 ± 40 W) and lactates (6.4 ± 1.7 vs 8.8 ± 3.2 and 4.2 ± 1.5 vs 6.6 ± 2.7 mmol L(-1) at 1- and 5-min post-exercise) were observed for HC versus TC, respectively (p < 0.05). Increases (p < 0.05) in physical fatigue and pain perception during TTs did not differ between TC and HC (p > 0.30). Both trials resulted in significant post-exercise decreases in metabolite detecting receptors ASIC3, P2X4, TRPV1, and TRPV4; increases in adrenergic receptors α2a, α2c, and β1; decreases in adrenergic β2, the immune receptor TLR4, and dopamine (DRD4); and increases in serotonin (HTR1D) and IL-10 (p < 0.05). Post-exercise IL-6 differed between TC and HC, with significantly greater increases observed following HC (p < 0.05).
CONCLUSIONS: Both TT performances appeared to be regulated around a specific sensory perception of fatigue and pain. Heat stress may have compensated for lower lactate during HC, thereby matching changes in metabolite detecting and other mRNAs across conditions.

A growing body of evidence indicates that extracellular nucleotides released or leaked from non-excitable cells as well as neurons play important roles in the regulation of neuronal and glial functions in the whole body through ATP receptors. ATP receptors (ionotropic P2X and metabotropic P2Y receptors) are the most abundant receptor families in living organisms. In the central nervous system, these receptors participate in synaptic transmission and in intercellular communications between neurons and glia. Glia cells are classified into astrocytes, oligodendrocytes and microglia. There are many reports on the role of ATP receptors (P2X4, P2X7, P2Y6 and P2Y12 receptors) expressed in spinal microglia. We have reported that several molecules presumably activate microglia in neuropathic pain after peripheral nerve injury. P2X4 receptors expressed in microglia in particular play a critical role in neuropathic pain signaling. The expression and activity of P2X4 receptors are up-regulated and enhanced predominantly in activated microglia in the spinal cord where damaged sensory fibers project. These findings provide novel targets for developing new medicines to treat neuropathic pain.

OBJECTIVE: To study using immunohistochemistry the localization of P2X receptor subtypes on the head of immature sperm in the human, mouse, hamster, and rat caput epididymidis.
METHODS: Basic research.
METHODS: University-based hospital.
METHODS: Three human epididymides were obtained from patients undergoing orchidectomy for metastatic prostate cancer.
METHODS: P2X(1), P2X(2), P2X(3), and P2X(4) receptor immunolocalization on sperm.
RESULTS: In the present study, P2X(1,2, and 3) receptor localization was immunohistochemically demonstrated on the head of immature sperm in the human, mouse, hamster, and rat caput epididymidis. P2X(4) receptor immunostaining was also observed on the head of sperm in the caput epididymidis of mice, hamsters, and humans, but not rats. There was a subsequent loss of receptor staining on sperm in the cauda epididymidis, except in humans where staining of P2X(4) receptors persisted. Comparision with peanut agglutinin (PNA) binding studies suggested the P2X receptors were located on the acrosome membrane. P2X(5-7) receptors were examined but found to be absent.
CONCLUSIONS: The change in localization of receptor subtypes is coincidental with the functionally essential morphologic and maturational changes seen in sperm as they travel through the epididymis, and is suggestive of a role for purinergic signaling in sperm maturation and possibly fertility.

In this study we have studied decavanadate effects at P2X receptors. Decavanadate competitively blocked 2\'- and 3\'-O-(4benzoylbenzoyl) ATP (BzATP) stimulated ethidium accumulation in HEK293 cells expressing human recombinant P2X7 receptors (pK(B) 7.5). The effects of decavanadate were rapid (minutes) in both onset and offset and contrasted with the much slower kinetics of pyridoxal 5-phosphate (P5P), Coomassie brilliant blue (CBB) and 1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine (KN62). Decavanadate competitively blocked the slowly reversible, or irreversible, blockade of the P2X7 receptor produced by P5P and oxidised ATP suggesting competition for a common binding site. However, the interaction between decavanadate and KN62 was non-competitive. Decavanadate also blocked P2X2 and P2X4 receptors but with slightly lower potency. These data demonstrate that decavanadate is the first reversible and competitive antagonist of the P2X7 receptor and is a useful tool for studying the mechanism of interaction of ligands with the P2X7 receptor.

Using immunohistological techniques and available polyclonal antibodies, we have identified several ATP-sensitive P2 receptor subtypes in specific structures of the normal rat kidney. Of the P2 receptor subtypes examined, P2X1, P2X2 and P2Y1 receptors were found in the smooth muscle layer of intrarenal vessels. The P2Y1 receptor was also found on glomerular mesangial cells, the brush border membrane of the proximal straight tubule and on peritubular fibroblasts. In the cortex, P2Y4 receptors were found on the tubule epithelium of the proximal convoluted tubule, and P2Y2 receptors on glomerular epithelial cells (podocytes). P2X4 and P2X6 receptors were present throughout the renal tubule epithelium from the proximal tubule to the collecting duct. P2X5 receptors were expressed on medullary collecting duct cells and the apical membrane of the S3 segment of the proximal tubule. Possible functions of these receptor subtypes in normal rat kidney are discussed.