Comparative quantification of dietary supplemented neural creatine concentrations with (1)H-MRS peak fitting and basis spectrum methods.

Magnetic resonance spectroscopy (MRS) is an analytical procedure that can be used to non-invasively measure the concentration of a range of neural metabolites. Creatine is an important neurometabolite with dietary supplementation offering therapeutic potential for neurological disorders with dysfunctional energetic processes. Neural creatine concentrations can be probed using proton MRS and quantified using a range of software packages based on different analytical methods. This experiment examines the differences in quantification performance of two commonly used analysis packages following a creatine supplementation strategy with potential therapeutic application. Human participants followed a seven day dietary supplementation regime in a placebo-controlled, cross-over design interspersed with a five week wash-out period. Spectroscopy data were acquired the day immediately following supplementation and analyzed with two commonly-used software packages which employ vastly different quantification methods. Results demonstrate that neural creatine concentration was augmented following creatine supplementation when analyzed using the peak fitting method of quantification (105.9%±10.1). In contrast, no change in neural creatine levels were detected with supplementation when analysis was conducted using the basis spectrum method of quantification (102.6%±8.6). Results suggest that software packages that employ the peak fitting procedure for spectral quantification are possibly more sensitive to subtle changes in neural creatine concentrations. The relative simplicity of the spectroscopy sequence and the data analysis procedure suggest that peak fitting procedures may be the most effective means of metabolite quantification when detection of subtle alterations in neural metabolites is necessary. The straightforward technique can be used on a clinical magnetic resonance imaging system.

Acute hypoxic gas breathing severely impairs cognition and task learning in humans.

Impairments in neural function are common when oxygen supply to the brain is reduced. This study examined neurocognitive processes that are vulnerable to oxygen deprivation. We induced moderate-to-severe hypoxia in healthy adults, thereby inducing impairments caused by low brain oxygen availability. 22 healthy adults participated in this matched-pairs study with a single-blind, randomised design. Baseline neurocognitive function was examined during a familiarisation trial and participants were assigned to hypoxia (10% O2) or sham (21% O2) groups. Neurocognitive performance was assessed via computerised test battery after 50 min of breathing a gas mixture that reduced arterial oxygen saturation by 20% (p<0.01). Hypoxia severely reduced performance across all neurocognitive domain scores; with significant drops in neurocognitive index (-20%), composite memory (-30%), verbal memory (-34%), visual memory (-23%), processing speed (-36%), executive function (-20%), psychomotor speed (-24%), reaction time (-10%), complex attention (-19%) and cognitive flexibility (-18%; all p<0.05). Practice effects were blocked by hypoxia but occurred in sham for information processing speed (+30%), executive function (+14%), psychomotor speed (+18%), reaction time (+5%), cognitive flexibility (+14%), and overall cognitive functioning (+9%; all p<0.05). Neuropsychological performance decrements caused by acute experimental hypoxia are comparable to cognitive domains impaired with high altitude exposure and mild traumatic brain injury.

Creatine supplementation enhances corticomotor excitability and cognitive performance during oxygen deprivation.

Impairment or interruption of oxygen supply compromises brain function and plays a role in neurological and neurodegenerative conditions. Creatine is a naturally occurring compound involved in the buffering, transport, and regulation of cellular energy, with the potential to replenish cellular adenosine triphosphate without oxygen. Creatine is also neuroprotective in vitro against anoxic/hypoxic damage. Dietary creatine supplementation has been associated with improved symptoms in neurological disorders defined by impaired neural energy provision. Here we investigate, for the first time in humans, the utility of creatine as a dietary supplement to protect against energetic insult. The aim of this study was to assess the influence of oral creatine supplementation on the neurophysiological and neuropsychological function of healthy young adults during acute oxygen deprivation. Fifteen healthy adults were supplemented with creatine and placebo treatments for 7 d, which increased brain creatine on average by 9.2%. A hypoxic gas mixture (10% oxygen) was administered for 90 min, causing global oxygen deficit and impairing a range of neuropsychological processes. Hypoxia-induced decrements in cognitive performance, specifically attentional capacity, were restored when participants were creatine supplemented, and corticomotor excitability increased. A neuromodulatory effect of creatine via increased energy availability is presumed to be a contributing factor of the restoration, perhaps by supporting the maintenance of appropriate neuronal membrane potentials. Dietary creatine monohydrate supplementation augments neural creatine, increases corticomotor excitability, and prevents the decline in attention that occurs during severe oxygen deficit. This is the first demonstration of creatine's utility as a neuroprotective supplement when cellular energy provision is compromised.

Carbohydrate in the mouth enhances activation of brain circuitry involved in motor performance and sensory perception.

The presence of carbohydrate in the human mouth has been associated with the facilitation of motor output and improvements in physical performance. Oral receptors have been identified as a potential mode of afferent transduction for this novel form of nutrient signalling that is distinct from taste. In the current study oral exposure to carbohydrate was combined with a motor task in a neuroimaging environment to identify areas of the brain involved in this phenomenon. A mouth-rinsing protocol was conducted whilst carbohydrate (CHO) and taste-matched placebo (PLA) solutions were delivered and recovered from the mouths of 10 healthy volunteers within a double-blind, counterbalanced design. This protocol eliminates post-oral factors and controls for the perceptual qualities of solutions. Functional magnetic resonance imaging of the brain was used to identify cortical areas responsive to oral carbohydrate during rest and activity phases of a hand-grip motor task. Mean blood-oxygen-level dependent signal change experienced in the contralateral primary sensorimotor cortex was larger for CHO compared with PLA during the motor task when contrasted with a control condition. Areas of activation associated with CHO exclusively were observed over the primary taste cortex and regions involved in visual perception. Regions in the limbic system associated with reward were also significantly more active with CHO. This is the first demonstration that oral carbohydrate signalling can increase activation within the primary sensorimotor cortex during physical activity and enhance activation of neural networks involved in sensory perception.

Exaggerated renal fibrosis in P2X4 receptor-deficient mice following unilateral ureteric obstruction.

BACKGROUND: The ATP-sensitive P2X7 receptor (P2X7R) has been shown to contribute to renal injury in nephrotoxic nephritis, a rodent model of acute glomerulonephritis, and in unilateral ureteric obstruction (UUO), a rodent model of chronic interstitial inflammation and fibrosis. Renal tubular cells, endothelial cells and macrophages also express the closely related P2X4 receptor (P2X4R), which is chromosomally co-located with P2X7R and has 40% homology; it is also pro-inflammatory and has been shown to interact with P2X7R to modulate its pro-apoptotic and pro-inflammatory effects. Therefore, we chose to explore the function of P2X4R in the UUO model of renal injury using knockout mice. We hypothesized that UUO-induced tubulointerstitial damage and fibrosis would also be attenuated in P2X4R(-/-) mice. METHOD: P2X4R(-/-) and wild-type (WT) mice were subjected to either UUO or sham operation. Kidney samples taken on Days 7 and 14 were evaluated for renal inflammation and fibrosis, and expression of pro-fibrotic factors. RESULTS: To our surprise, the obstructed kidney in P2X4R(-/-) mice showed more severe renal injury, more collagen deposition (picrosirius red staining, increase of 53%; P < 0.05) and more type I collagen staining (increase of 107%; P < 0.01), as well as increased mRNA for TGF-ß (increase of 102%, P < 0.0005) and CTGF (increase of 157%; P < 0.05) by Day 14, compared with the UUO WT mice. CONCLUSION: These findings showed that lack of P2X4R expression leads to increased renal fibrosis, and increased expression of TGF-ß and CTGF in the UUO model.

Is the inflammasome a potential therapeutic target in renal disease?

The inflammasome is a large, multiprotein complex that drives proinflammatory cytokine production in response to infection and tissue injury. Pattern recognition receptors that are either membrane bound or cytoplasmic trigger inflammasome assembly. These receptors sense danger signals including damage-associated molecular patterns and pathogen-associated molecular patterns (DAMPS and PAMPS respectively). The best-characterized inflammasome is the NLRP3 inflammasome. On assembly of the NLRP3 inflammasome, post-translational processing and secretion of pro-inflammatory cytokines IL-1ß and IL-18 occurs; in addition, cell death may be mediated via caspase-1. Intrinsic renal cells express components of the inflammasome pathway. This is most prominent in tubular epithelial cells and, to a lesser degree, in glomeruli. Several primary renal diseases and systemic diseases affecting the kidney are associated with NLRP3 inflammasome/IL-1ß/IL-18 axis activation. Most of the disorders studied have been acute inflammatory diseases. The disease spectrum includes ureteric obstruction, ischaemia reperfusion injury, glomerulonephritis, sepsis, hypoxia, glycerol-induced renal failure, and crystal nephropathy. In addition to mediating renal disease, the IL-1/ IL-18 axis may also be responsible for development of CKD itself and its related complications, including vascular calcification and sepsis. Experimental models using genetic deletions and/or receptor antagonists/antiserum against the NLRP3 inflammasome pathway have shown decreased severity of disease. As such, the inflammasome is an attractive potential therapeutic target in a variety of renal diseases.

Purinergic signaling in inflammatory renal disease.

Extracellular purines have a role in renal physiology and adaption to inflammation. However, inflammatory renal disease may be mediated by extracellular purines, resulting in renal injury. The role of purinergic signaling is dependent on the concentrations of extracellular purines. Low basal levels of purines are important in normal homeostasis and growth. Concentrations of extracellular purines are significantly elevated during inflammation and mediate either an adaptive role or propagate local inflammation. Adenosine signaling mediates alterations in regional renal blood flow by regulation of the renal microcirculation, tubulo-glomerular feedback, and tubular transport of sodium and water. Increased extracellular ATP and renal P2 receptor-mediated inflammation are associated with various renal diseases, including hypertension, diabetic nephropathy, and glomerulonephritis. Experimental data suggests P2 receptor deficiency or receptor antagonism is associated with amelioration of antibody-mediated nephritis, suggesting a pathogenic (rather than adaptive) role of purinergic signaling. We discuss the role of extracellular nucleotides in adaptation to ischemic renal injury and in the pathogenesis of inflammatory renal disease.

P2 receptors in renal pathophysiology.

Our knowledge and understanding of the P2 receptor signalling system in the kidney have increased significantly in the last ten years. The broad range of physiological roles proposed for this receptor system and the variety of P2 receptor subtypes found in the kidney suggest that any disturbance of function may contribute to several pathological processes. So far, most reports of a possible pathophysiological role for this system in the kidney have focussed on polycystic kidney disease, where abnormal P2 receptor signalling might be involved in cyst expansion and disease progression, and on the P2X(7) receptor, a unique P2X subtype, which when activated enhances inflammatory cytokine release and production, and also cell death. Expression of this particular receptor is upregulated in some forms of chronic renal injury and inflammatory diseases. Further studies of adenosine triphosphate signalling and P2 receptor expression in renal disorders could provide us with novel insights into the role of these receptors in both normal and abnormal kidney function.

P2X7 deficiency attenuates renal injury in experimental glomerulonephritis.

The P2X7 receptor is a ligand-gated cation channel that is normally expressed by a variety of immune cells, including macrophages and lymphocytes. Because it leads to membrane blebbing, release of IL-1beta, and cell death by apoptosis or necrosis, it is a potential therapeutic target for a variety of inflammatory diseases. Although the P2X7 receptor is usually not detectable in normal renal tissue, we previously reported increased expression of both mRNA and protein in mesangial cells and macrophages infiltrating the glomeruli in animal models of antibody-mediated glomerulonephritis. In this study, we used P2X7-knockout mice in the same experimental model of glomerulonephritis and found that P2X7 deficiency was significantly renoprotective compared with wild-type controls, evidenced by better renal function, a striking reduction in proteinuria, and decreased histologic glomerular injury. In addition, the selective P2X7 antagonist A-438079 prevented the development of antibody-mediated glomerulonephritis in rats. These results support a proinflammatory role for P2X7 in immune-mediated renal injury and suggest that the P2X7 receptor is a potential therapeutic target.

Sodium-dependent regulation of renal amiloride-sensitive currents by apical P2 receptors.

The epithelial sodium channel (ENaC) plays a major role in the regulation of sodium balance and BP by controlling Na(+) reabsorption along the renal distal tubule and collecting duct (CD). ENaC activity is affected by extracellular nucleotides acting on P2 receptors (P2R); however, there remain uncertainties over the P2R subtype(s) involved, the molecular mechanism(s) responsible, and their physiologic role. This study investigated the relationship between apical P2R and ENaC activity by assessing the effects of P2R agonists on amiloride-sensitive current in the rat CD. Using whole-cell patch clamp of principal cells of split-open CD from Na(+)-restricted rats, in combination with immunohistochemistry and real-time PCR, we found that activation of metabotropic P2R (most likely the P2Y(2) and/or (4) subtype), via phospholipase C, inhibited ENaC activity. In addition, activation of ionotropic P2R (most likely the P2X(4) and/or (4/6) subtype), via phosphatidylinositol-3 kinase, either inhibited or potentiated ENaC activity, depending on the extracellular Na(+) concentration; therefore, it is proposed that P2X(4) and/or (4/6) receptors might function as apical Na(+) sensors responsible for local regulation of ENaC activity in the CD and could thereby help to regulate Na(+) balance and systemic BP.

Spheres of influence or autonomy? A discourse analysis of the introduction of Nurse Practitioners in rural and remote Australia.

AIM: This paper is a report of a study to examine the social discourses of nursing within health care as these produce understandings about autonomy for Nurse Practitioners, where autonomy refers to the ability of Nurse Practitioners to practise as professionals in their own right. BACKGROUND: Nurse Practitioners were recently introduced to the nursing career pathways in Australia. Despite a plethora of international information, the role implementation in rural and remote Australia is slow with a number of influences emerging to hinder progress. METHOD: Critical discourse analysis was used to examine the differences between policy and the reality of implementation. The notion of autonomy was used to explore texts in policy documents relating to Nurse Practitioner authorization and published between 1995 and 2006, and these were compared with the experiences of nurses working in Nurse Practitioner positions. FINDINGS: Policy texts indicate support for advanced practice and the autonomy of Nurse Practitioners. The process for authorization; however, has constraints which support nurses' progress but also hinder it. Subsequent acceptance of Nurse Practitioners has also been problematic as colleagues struggle to understand the role within the current healthcare system. CONCLUSIONS: There is a significant gap between the rhetoric of policy and the implementation of Nurse Practitioner roles in rural and remote Australia. Whilst policy supports the notion of autonomy, the experiences of nurses indicate a mere shift in the traditionally-accepted boundaries of nurses' roles. Evidence from the United Kingdom and United States of America suggests that the findings in this study are relevant internationally as well as nationally.

Antagonism of endogenous putative P2Y receptors reduces the growth of MDCK-derived cysts cultured in vitro.

P2Y receptors couple to G proteins and either mobilize intracellular Ca(2+) or alter cAMP levels to modulate the activity of Ca(2+)- and cAMP-sensitive ion channels. We hypothesize that increased ion transport into the lumen of MDCK cysts can osmotically drive fluid movement and increase cyst size. Furthermore, activation of the adenylate cyclase/cAMP pathway may trigger cell proliferation via an extracellular signal-related kinase cascade. To test this hypothesis, several P2Y receptor inhibitors were used on the MDCK in vitro model of renal cyst formation. The nonspecific P2 receptor inhibitors reactive blue 2 and suramin reduced cyst growth significantly, as did PPADS and, to a lesser extent, the P2Y(1)-specific antagonist MRS2179. Cyst growth was reduced by approximately 50% when ATP was removed from the culture medium with apyrase, although stable analogs of ATP failed to increase cyst size. The nonselective P2X receptor inhibitor Coomassie brilliant blue G was ineffective at reducing cyst growth, suggesting no involvement of P2X receptors. Finally, the presence of selective inhibitors of ERK activation (either PD98059 or U0126) greatly reduced cyst growth, whereas in untreated cysts ERK activity was observed to increase with time. We conclude that stimulation of endogenous P2Y receptors by extracellular ATP increases growth of MDCK cysts via cAMP-dependent activation of the ERK pathway. P2Y receptor antagonists may have therapeutic potential in reducing cyst size and slowing disease progression; although further studies in vitro and in vivo are needed to investigate the specificity and role of these P2Y receptors in renal cystic diseases.

Increased expression of the pro-apoptotic ATP-sensitive P2X7 receptor in experimental and human glomerulonephritis.

BACKGROUND: The involvement of IL-1beta and other pro-inflammatory cytokines in most forms of glomerulonephritis is now well established. The P2X(7) receptor, an ATP-sensitive P2X receptor, functions not only as a non-selective cation channel, but it is also involved in the rapid processing and release of IL-1beta, apoptosis and necrotic cell death. Therefore, we wanted to investigate if expression of this receptor is altered in the glomeruli of rodent models of glomerulonephritis. METHODS: P2X(7) receptor protein expression was investigated using immunohistochemistry, and apoptosis was assessed using the TUNEL assay and caspase-3 immunostaining. Real-time PCR with gene-specific primers was used to detect P2X(7), IL-1beta, p53, bax and bcl-2 mRNA expression. RESULTS: Although the levels of the P2X(7) receptor protein in mouse kidney are normally very low, or undetectable, we detected an increase in glomerular expression of this receptor and an increase in glomerular apoptotic cells in a mouse model of accelerated nephrotoxic nephritis. We also observed increased glomerular and tubular expression of the P2X(7) receptor protein in renal biopsy tissue of patients with autoimmune-related glomerulonephritis. Furthermore, P2X(7) receptor mRNA increased in the kidneys of a rat model of proliferative glomerulonephritis and this coincided with the onset of proteinuria. We also observed increased mRNA expression of Il-1beta and the pro-apoptotic markers p53 and bax, but not of anti-apoptotic bcl-2. CONCLUSION: Although there is an association between expression of the pro-inflammatory and pro-apoptotic P2X(7) receptor and glomerulonephritis in these rodent models, and in at least one form of human glomerulonephritis, the underlying relationship and its functional significance remain to be explored.

Bone mineral density among female sports participants.

Training for and participation in impact-loading sports are associated with alterations in bone strength which are specific to anatomical site and type of strain. The effect of exercise on bone mineral density (BMD) depends on the type of activity engaged in. Sports with high impact loading seem to have a positive effect in promoting bone mineralisation, whereas those with low impacts may have negative or no effects. The aims of the present study were to compare BMD and body composition measures among female participants in three distinctly different sports and investigate differences from sedentary control subjects. Participants were club and university level Rugby Union football players (n = 30, age: 21.4 +/- 1.9 years, height: 1.67 +/- 0.05 m, mass: 73.3 +/- 10.7 kg), netball players (n = 20, 20.7 +/- 1.3 years, 1.68 +/- 0.07 m, 64.3 +/- 7.2 kg), distance runners (n = 11, 21.5 +/- 2.6 years, 1.68 +/- 0.04 m, 57.1 +/- 6.1 kg), and sedentary controls (n = 25, 21.4 +/- 1.1 years; 1.64 +/- 0.07 m, 56.8 +/- 6.8 kg). With the exception of three distance runners, all participants were eumenorrhoeic. Bone mineral density scans were performed for whole-body, left proximal femur, and lumbar spine (L1-4) using dual-energy X-ray absorptiometry. Fat mass, percent body fat, and fat-free soft tissue mass were assessed from whole-body scans. Regional and segmental analysis was also carried out on whole-body BMD data using standard procedures. The runners had a lower fat mass and percent body fat compared to the other sports participants and the controls. All sports groups had higher BMD values than had the controls. Density of bone in the upper body was most pronounced in the rugby football players and least pronounced in the runners. Positive effects were evident at all sites for the rugby players. There were significant correlations between BMD and fat-free soft tissue mass, BMD and body mass, and BMD and training volume. It is concluded that sports participation has positive effects on BMD. The effects are site-specific and depend on the loading characteristics of the sport.

Glomerular expression of the ATP-sensitive P2X receptor in diabetic and hypertensive rat models.

BACKGROUND: The molecular identification and characterization of the adenosine triphosphate (ATP)-sensitive family of P2 receptors is comparatively new. There are two main subgroups, each with several subtypes and widespread tissue distribution, including the kidney. A unique member of the P2X subgroup of P2 receptors is the ATP-gated ion channel P2X(7), which on activation can cause cell blebbing, cytokine release, and cell death by necrosis or apoptosis. We report expression of this receptor in normal rat kidney and in two chronic models of glomerular injury: streptozotocin-induced (STZ) diabetes and ren-2 transgenic (TGR) hypertension. METHODS: At different time points in these models, we used a polyclonal antibody to the P2X(7) receptor and immunohistochemistry to determine its expression and distribution. We also used Western blotting and real-time polymerase chain reaction (PCR) to detect changes in P2X(7) receptor protein and mRNA expression, respectively. RESULTS: We found only low-level glomerular immuno-staining for the P2X(7) receptor in normal rat kidney, but intense P2X(7) receptor immunostaining of glomeruli in kidneys from diabetic animals at 6 and 9 weeks, and in hypertensive animals at 12 weeks. In diabetic animals, real-time PCR demonstrated a approximately tenfold increase in glomerular P2X(7) receptor mRNA relative to control, and Western blotting confirmed an increase in protein. Immunohistochemistry and immunoelectron microscopy showed staining of glomerular podocytes, which was both intracellular and at the plasma membrane. CONCLUSION: We conclude that the P2X(7) receptor is not expressed appreciably under normal conditions, but that following glomerular injury it is significantly up-regulated, mainly in podocytes, though also in endothelial and mesangial cells, of animals with STZ-induced diabetes mellitus or TGR hypertension. Although the exact function and regulation of this receptor remain unclear, its association with inflammatory cytokine release and cell death suggests that increased expression might be involved in the pathogenesis of glomerular cell injury or repair.

The isolated polycystin-1 cytoplasmic COOH terminus prolongs ATP-stimulated Cl- conductance through increased Ca2+ entry.

The precise steps leading from mutation of the polycystic kidney disease (PKD1) gene to the autosomal dominant polycystic kidney disease (ADPKD) phenotype remain to be established. Fluid accumulation is a requirement for cyst expansion in ADPKD, suggesting that abnormal fluid secretion into the cyst lumen might play a role in disease. In this study, we sought to establish a link between polycystin-1 (the PKD1 gene product) and ATP-stimulated Cl- secretion in renal tubule cells. To do this, we performed a whole cell patch-clamp analysis of the effects of expression of the isolated cytoplasmic COOH-terminus of polycystin-1 in stably transfected mouse cortical collecting duct cells. The truncated polycystin-1 fusion protein prolonged the duration of ATP-stimulated Cl- conductance and intracellular Ca2+ responses. Both effects were dependent on extracellular Ca2+. It was determined that expression of the truncated polycystin-1 fusion protein introduced, or activated, an ATP-induced Ca2+ entry pathway that was undetectable in transfection control cell lines. Our findings are concordant with increasing evidence for a role of polycystin-1 in cell Ca2+ homeostasis and indicate that dysregulated Ca2+ entry might promote Cl- secretion and cyst expansion in ADPKD.

Nurse practitioners: a contract for change and excellence in nursing.

The role of the Nurse Practitioner has been in existence in a variety of contexts and within a broad range of the scope of their practice throughout the world for a number of years. Many nurses work at this advanced level of clinical practice without the acknowledgement f the very important and responsible role that they play within the healthcare setting. Although the United States and United Kingdom have recognised the role of the advanced Nurse Practitioner for a number of years, there still exists confusion and disagreement as to their scope of practice. There is uncertainty and anxiety as to where the role boundaries between nursing and medical and allied health professionals begin and end. The role of the Nurse Practitioner in Australia has not been without its problems in the developmental stage of its creation. New South Wales finally achieved recognition of the role this year after a decade of negotiation. This has culminated in the acceptance for the development of 40 Nurse Practitioner positions across the State. The first of these was accepted in the Far West Area Health Service in May 2001. The Far West Area Health Service created a five-year plan, which addresses the development of nurses preparing for authorisation, the creation of Nurse Practitioner positions in the remote communities, the creation of clinical guidelines to support advanced practice and the evaluation process for both the positions and the nurses. The objective of this approach is to ensure effective implementation of these advanced nursing positions in the remote communities of New South Wales. The Nurse Practitioner role needs to respond to the individual, the family and the community, utilising advanced clinical skills and remaining responsive to the changes in health care within a primary health care framework, which is essential for combating the complex health care issues in remote areas (NSW Health 2000).

Evidence for basolateral P2Y(6) receptors along the rat proximal tubule: functional and molecular characterization.

In this study, the distribution of P2Y(6) receptor mRNA in rat nephron segments was investigated and a functional approach was used to analyze basolateral protein expression. Reverse transcription-PCR studies revealed more intense expression of P2Y(6) receptor mRNA in the proximal tubule and the thick ascending limb of Henle's loop, less intense expression in the thin descending limb and the cortical and outer medullary collecting ducts, and no detectable expression in either the thin ascending limb or the inner medullary collecting duct. Dose-dependent calcium responses to basolateral administration of UDP (a selective agonist for the P2Y(6) receptor) were observed in the proximal tubule but not in any of the other segments studied. In the proximal tubule, intracellular calcium concentration changes induced by UDP were associated with increased production of inositol phosphates, as were those induced by ATP and norepinephrine. However, UDP-induced intracellular calcium concentration changes were different, exhibiting no plateau after the initial peak; moreover, a single stimulation with a high concentration of UDP induced full desensitization of the UDP-sensitive calcium pathway but did not alter the responsiveness of the proximal tubule to ADP (a specific P2Y(1) receptor agonist), ATP or norepinephrine. In summary, this report demonstrates that P2Y(6) receptor mRNA is expressed in most segments of the rat nephron but that basolateral expression of the protein is restricted to the proximal tubule, where the receptor is coexpressed with the P2Y(1) receptor. The differences in the distributions of P2Y(6) receptor mRNA and UDP responses may indicate the presence of luminal receptors in other nephron segments.