22 research outputs found
Sympathetic nerve-derived ATP regulates renal medullary vasa recta diameter via pericyte cells: a role for regulating medullary blood flow?
Pericyte cells are now known to be a novel locus of blood flow control, being able to regulate capillary diameter via their unique morphology and expression of contractile proteins. We have previously shown that exogenous ATP causes constriction of vasa recta via renal pericytes, acting at a variety of membrane bound P2 receptors on descending vasa recta (DVR), and therefore may be able to regulate medullary blood flow (MBF). Regulation of MBF is essential for appropriate urine concentration and providing essential oxygen and nutrients to this region of high, and variable, metabolic demand. Various sources of endogenous ATP have been proposed, including from epithelial, endothelial, and red blood cells in response to stimuli such as mechanical stimulation, local acidosis, hypoxia, and exposure to various hormones. Extensive sympathetic innervation of the nephron has previously been shown, however the innervation reported has focused around the proximal and distal tubules, and ascending loop of Henle. We hypothesize that sympathetic nerves are an additional source of ATP acting at renal pericytes and therefore regulate MBF. Using a rat live kidney slice model in combination with video imaging and confocal microscopy techniques we firstly show sympathetic nerves in close proximity to vasa recta pericytes in both the outer and inner medulla. Secondly, we demonstrate pharmacological stimulation of sympathetic nerves in situ (by tyramine) evokes pericyte-mediated vasoconstriction of vasa recta capillaries; inhibited by the application of the P2 receptor antagonist suramin. Lastly, tyramine-evoked vasoconstriction of vasa recta by pericytes is significantly less than ATP-evoked vasoconstriction. Sympathetic innervation may provide an additional level of functional regulation in the renal medulla that is highly localized. It now needs to be determined under which physiological/pathophysiological circumstances that sympathetic innervation of renal pericytes is important
An Intact Kidney Slice Model to Investigate Vasa Recta Properties and Function in situ
Background: Medullary blood flow is via vasa recta capillaries, which possess contractile pericytes. In vitro studies using isolated descending vasa recta show that pericytes can constrict/dilate descending vasa recta when vasoactive substances are present. We describe a live kidney slice model in which pericyte-mediated vasa recta constriction/dilation can be visualized in situ. Methods: Confocal microscopy was used to image calcein, propidium iodide and Hoechst labelling in âliveâ kidney slices, to determine tubular and vascular cell viability and morphology. DIC video-imaging of live kidney slices was employed to investigate pericyte-mediated real-time changes in vasa recta diameter. Results: Pericytes were identified on vasa recta and their morphology and density were characterized in the medulla. Pericyte-mediated changes in vasa recta diameter (10â30%) were evoked in response to bath application of vasoactive agents (norepinephrine, endothelin-1, angiotensin-II and prostaglandin E2) or by manipulating endogenous vasoactive signalling pathways (using tyramine, L-NAME, a cyclo-oxygenase (COX-1) inhibitor indomethacin, and ATP release). Conclusions: The live kidney slice model is a valid complementary technique for investigating vasa recta function in situ and the role of pericytes as regulators of vasa recta diameter. This technique may also be useful in exploring the role of tubulovascular crosstalk in regulation of medullary blood flow
NÀtpokern i Sverige : - En sociologisk litteraturstudie av fenomenet nÀtpoker
Denna magisteruppsats i sociologi Ă€r en litteraturstudie om fenomenet nĂ€tpoker. Studier inom Ă€mnet har granskats och analyserats utifrĂ„n mitt syfte och mina frĂ„gestĂ€llningar. Syftet med studien Ă€r att skapa en djupare sociologisk förstĂ„else för fenomenet nĂ€tpoker och dess konsekvenser genom att kartlĂ€gga och analysera den svenska forskningen inom Ă€mnesomrĂ„det. FrĂ„gestĂ€llningarna som jag har utgĂ„tt ifrĂ„n lyder enligt följande; Hur kan man förstĂ„ utbredandet av fenomenet nĂ€tpoker?, GĂ„r det â utifrĂ„n min definition av klassbegreppet â att anlĂ€gga ett klassperspektiv pĂ„ nĂ€tpokerspelarna och kan en person förĂ€ndra sin livsstil med hjĂ€lp av nĂ€tpoker?, Ăr vissa grupper i samhĂ€llet överrepresenterade bland nĂ€tpokerspelarna och hur kan detta i sĂ„ fall förstĂ„s? samt PĂ„ vilket sĂ€tt kan nĂ€tpokerspelande orsaka spelberoende och hur kan den svenska folkhĂ€lsan pĂ„verkas av nĂ€tpoker? Arbetet med denna studie visade bland annat att nĂ€tpokerns utbreddhet till stor del beror pĂ„ dess tillgĂ€nglighet, via Internet. Vidare har jag med hjĂ€lp av min studie kunnat konstatera att det Ă€r svĂ„rt att anlĂ€gga ett klassperspektiv pĂ„ nĂ€tpokerspelarna dĂ„ andra faktorer kan förklara varför vissa grupper Ă€r överrepresenterade nĂ€tpokerspelare. Vidare visade resultatet att nĂ€tpoker utgör ett högriskspel med avseende pĂ„ spelberoende pĂ„ grund av faktorer som dess extrema lĂ€ttillgĂ€nglighet samt dess skicklighetsaspekt. De teman som den svenska forskningen om nĂ€tpoker har hĂ„llit sig till Ă€r Internets pĂ„verkan och dess konsekvenser, spelbeteende samt spelmarknaden, vilket kan jĂ€mföras med den internationella forskningen som ocksĂ„ har hĂ„llit sig till temat spelbeteende men som Ă€ven mer har hĂ„llit sig till teman som nĂ€tpokern som nytt fenomen, studenterna och nĂ€tpokern samt den juridiska aspekten av nĂ€tpoker
Extracellular nucleotides affect pericyte-mediated regulation of rat in situ vasa recta diameter.
AIM
We hypothesized that extracellular nucleotides, established as being released from renal tubular epithelial cells, act at pericytes to regulate vasa recta capillary diameter.
METHODS
A rat live kidney slice model and video imaging techniques were used to investigate the effects of extracellular nucleotides on in situ (subsurface) vasa recta diameter at pericyte and non-pericyte sites. In addition, RT-qPCR was used to quantify P2 receptor mRNA expression in isolated vasa recta.
RESULTS
Extracellular ATP, UTP, benzylbenzyl ATP (BzATP) or 2-methylthioATP (2meSATP) evoked a significantly greater vasoconstriction of subsurface vasa recta at pericytes than at non-pericyte sites. The rank order of agonist potency was BzATP = 2meSATP > ATP = UTP. The vasoconstriction evoked at pericyte sites by ATP was significantly attenuated by the P2 receptor antagonists suramin, pyridoxal phosphate-6-azo(benzene-2,4-disulfonic acid) (PPADS) or Reactive Blue-2 (RB-2). UTP-evoked vasoconstriction at pericytes was attenuated by suramin or RB-2 but not PPADS. Interestingly, suramin or PPADS, when applied in the absence of a P2 receptor agonist, evoked a weak but significant vasoconstriction of vasa recta at pericyte sites, suggesting tonic vasodilation by nucleotides. Significant levels of P2X(1, 3 and 7) and P2Y(4 and 6) receptor mRNA were detected in vasa recta.
CONCLUSION
Extracellular nucleotides act at pericytes to cause vasoconstriction of in situ vasa recta. Pharmacological characterization, supported by RT-qPCR data, suggests that P2X(1 and 7) and P2Y(4) receptors mediate nucleotide-evoked vasoconstriction of vasa recta by pericytes. We propose that nucleotides released from renal tubular epithelial cells, in close proximity to vasa recta capillaries, are key in regulating renal medullary blood flow
Supplementary Material for: An Intact Kidney Slice Model to Investigate Vasa Recta Properties and Function in situ
<p><b><i>Background:</i></b> Medullary blood flow is via vasa recta
capillaries, which possess contractile pericytes. In vitro studies using
isolated descending vasa recta show that pericytes can constrict/dilate
descending vasa recta when vasoactive substances are present. We
describe a live kidney slice model in which pericyte-mediated vasa recta
constriction/dilation can be visualized in situ. <b><i>Methods:</i></b>
Confocal microscopy was used to image calcein, propidium iodide and
Hoechst labelling in âliveâ kidney slices, to determine tubular and
vascular cell viability and morphology. DIC video-imaging of live kidney
slices was employed to investigate pericyte-mediated real-time changes
in vasa recta diameter. <b><i>Results:</i></b> Pericytes were identified
on vasa recta and their morphology and density were characterized in
the medulla. Pericyte-mediated changes in vasa recta diameter (10â30%)
were evoked in response to bath application of vasoactive agents
(norepinephrine, endothelin-1, angiotensin-II and prostaglandin E<sub>2</sub>) or by manipulating endogenous vasoactive signalling pathways (using tyramine, <i>L</i>-NAME, a cyclo-oxygenase (COX-1) inhibitor indomethacin, and ATP release). <b><i>Conclusions:</i></b>
The live kidney slice model is a valid complementary technique for
investigating vasa recta function in situ and the role of pericytes as
regulators of vasa recta diameter. This technique may also be useful in
exploring the role of tubulovascular crosstalk in regulation of
medullary blood flow.</p