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At least 1,045 records · Page 58Linked to original sources
PubMed2003

Hypoxia induces an autocrine-paracrine survival pathway via platelet-derived growth factor (PDGF)-B/PDGF-beta receptor/phosphatidylinositol 3-kinase/Akt signaling in RN46A neuronal cells.

In neurons, hypoxia activates intracellular death-related pathways, yet the antiapoptotic mechanisms triggered by hypoxia remain unclear. In RN46A neuronal cells, minimum media growth conditions induced cell death as early as 12 h after the cells were placed in these conditions (i.e., after removal of B-27 supplement). However, apoptosis occurred in hypoxia (1% O2) only after 48 h, and in fact hypoxia reduced the apoptosis associated with trophic factor withdrawal. Furthermore, hypoxia induced time-dependent increases in expression of platelet-derived growth factor (PDGF) B mRNA and protein, as well as PDGF-beta receptor phosphorylation. Although exogenous PDGF-BB induced only transient Akt activation, hypoxia triggered persistent activation of Akt for up to 24 h. Inhibition of phosphatidylinositol 3-kinase (PI3K) or of PDGF-beta receptor phosphorylation abrogated both hypoxia-induced and exogenous PDGF-BB-induced Akt phosphorylation, and it completely abolished hypoxia-induced protection from media supplement deprivation, which suggests that the long-lasting activation of Akt during hypoxia and the prosurvival induction were due to endogenously generated PDGF-BB. Furthermore, these inhibitors decreased hypoxia-inducible factor 1alpha (HIF-1alpha) DNA binding, which suggests that the PDGF/PDGF-beta receptor/Akt pathway induces downstream HIF-1alpha gene transcription. We conclude that in RN46A neuronal cells, hypoxia activates an autocrine-paracrine antiapoptotic mechanism that involves up-regulation of PDGF-B and PDGF-beta receptor-dependent activation of the PI3K/Akt signaling pathway to induce downstream transcription of survival genes.

Apoptosis↗
PubMed2004

Evidence of melatonin synthesis by human lymphocytes and its physiological significance: possible role as intracrine, autocrine, and/or paracrine substance.

It has been historically assumed that the pineal gland is the major source of melatonin (N-acetyl-5-methoxytryptamine) in vertebrates. Melatonin plays a central role in fine-tuning circadian rhythms in vertebrate physiology. In addition, melatonin shows a remarkable functional versatility exhibiting antioxidant, oncostatic, antiaging, and immunomodulatory properties. Melatonin has been identified in a wide range of organisms from bacteria to human beings. Its biosynthesis from tryptophan involves four well-defined intracellular steps catalyzed by tryptophan hydroxylase, aromatic amino acid decarboxylase, serotonin-N-acetyltransferase, and hydroxyindole-O-methyltransferase. Here, for the first time, we document that both resting and phytohemagglutinin-stimulated human lymphocytes synthesize and release large amounts of melatonin, with the melatonin concentration in the medium increasing up to five times the nocturnal physiological levels in human serum. Moreover, we show that the necessary machinery to synthesize melatonin is present in human lymphocytes. Furthermore, melatonin released to the culture medium is synthesized in the cells, because blocking the enzymes required for its biosynthesis or inhibiting protein synthesis in general produced a significant reduction in melatonin release. Moreover, this inhibition caused a decrease in IL-2 production, which was restored by adding exogenous melatonin. These findings indicate that in addition to pineal gland, human lymphoid cells are an important physiological source of melatonin and that this melatonin could be involved in the regulation of the human immune system, possibly by acting as an intracrine, autocrine, and/or paracrine substance.

Acetylserotonin O-Methyltransferase↗
PubMed2004

Interleukin-10 expression in lipopolysaccharide-activated microglia is mediated by extracellular ATP in an autocrine fashion.

Immune cells have been shown to release ATP into the extracellular space to provide auto- and paracrine purinergic modulation of immune and inflammatory responses. In the present study, we demonstrate that ATP released from lipopolysaccharide (LPS)-stimulated microglia induces interleukin-10 (IL-10) expression in an autocrine manner. The expression as well as secretion of IL-10 by LPS-stimulated microglia was completely inhibited by apyrase, ATP-hydrolyzing enzyme, whereas tumor necrosis factor-alpha (TNF-alpha) expression was unaffected. LPS-activated microglia rapidly released a low concentration of ATP (10-20 nM) into the medium, and the nanomolar range of extracellular ATP, ADP, adenosine 5'-O-(3-thiotriphosphate) (ATP-gamma-S), and adenosine 5'-O-(2-thiodiphosphate) (ADP-beta-S) induced IL-10 secretion from microglia in a dose-dependent manner. These results suggest that ATP released from LPS-activated microglia and/or a metabolite of ATP (ADP) may induce IL-10 expression through P2Y purinergic receptors.

Adenosine Triphosphate↗
PubMed2002

Autocrine and/or paracrine insulin-like growth factor-I activity in skeletal muscle.

Similar to bone, skeletal muscle responds and adapts to changes in loading state via mechanisms that appear to be intrinsic to the muscle. One of the mechanisms modulating skeletal muscle adaptation it thought to involve the autocrine and/or paracrine production of insulinlike growth factor-I. This brief review outlines components of the insulinlike growth factor-I system as it relates to skeletal muscle and provides the rationale for the theory that insulinlike growth factor-I is involved with muscle adaptation.

1-Phosphatidylinositol 4-Kinase↗
PubMed2003

Production of the novel mesangial autocrine growth factors GDNF and IL-10 is regulated by the immunomodulator AS101.

Mesangial cell (MC) proliferation is essential for the pathogenesis and progression of various glomerular diseases. This study shows that glial cell line-derived neurotrophic factor (GDNF) and IL-10 are mesangial autocrine growth factors that play a pivotal role in rat MC proliferation in vitro. Downstream targets of GDNF signaling and their role in MC hyperplasia are identified. The phosphatidylinositol 3-kinase (PI3K) pathway and its downstream target NF-kappaB were found to mediate GDNF-induced MC mitogenesis. This pathway also mediates GDNF-induced decrease in the cyclin-dependent kinase inhibitor p27(kip1) expression, resulting in the increased formation of cyclin D1/cdk4 and cyclin E/cdk2 complexes, followed by hyperphosphorylation of retinoblastoma, a key event for G1 to S phase progression. IL-10 appears to be a more potent MC growth factor that negatively regulates GDNF expression. Indeed, its inhibition by the nontoxic tellurium anti-IL-10 compound, ammonium trichloro(dioxoethylene-o,o') tellurate (AS101), extensively decreased MC clonogenicity despite GDNF upregulation. Identification of the mesangial GDNF and IL-10 pathways as critical mediators of mesangial cell proliferation may provide another target for therapeutic intervention in certain glomerular diseases. In vivo animal studies using AS101, currently undergoing phase II clinical trials on cancer patients, are warranted to determine its potential in the management of glomerular diseases associated with mesangial cell proliferation.

Adjuvants, Immunologic↗
PubMed2005

An autocrine or paracrine Fas-mediated counterattack: a potential mechanism for apoptosis of notochordal cells in intact rat nucleus pulposus.

STUDY DESIGN: Immunohistochemistry and in situ nick end-labeling (TUNEL) were performed in rat lumbar intervertebral discs. OBJECTIVES: To demonstrate the mechanism of notochordal cell death in the nucleus pulposus (NP). SUMMARY OF BACKGROUND DATA: With age, notochordal cells gradually disappear in the NP. We hypothesized that this phenomenon might be related to Fas-mediated apoptosis. MATERIALS AND METHODS: Expressions of Fas; Fas ligand (FasL); caspase 3, 8, 9, 10; Ki-67 protein; and TUNEL were examined in 4-week-, 6-month- and 12-month-old rat NPs. Apoptosis (TUNEL-positive) and proliferation potential (Ki-67-positive) indexes of notochordal cells were calculated and compared among age groups. RESULTS: Notochordal cells constitutively expressed both Fas and FasL. Among their downstream initiator (caspase 8, 9, and 10) and executioner (caspase 3) caspases tested, caspase 9 and 3 were expressed. Proliferation potential of the notochordal cells was the highest at 4 weeks (1.96 +/- 1.3%) and decreased to a significantly lower level at 6 (0.81 +/- 0.68%) and 12 months (0.8 +/- 0.37%; P = 0.03 and 0.01, respectively). In contrast, apoptosis of the notochordal cells was the lowest at 4 weeks (3.52 +/- 1.07%) and increased to a significantly higher level at 6 (19.38 +/- 10.99%) and 12 months (21.51 +/- 16.99%; P < 0.001 in both comparisons). CONCLUSIONS: Fas-mediated mitochondrial caspase 9 pathway is constitutively present in the rat notochordal cells. The constitutive expression of Fas, FasL and its downstream caspases, as well as the homogeneity ofnotochordal cell population suggests an autocrine or paracrine Fas-mediated counterattack to be a potential mechanism for apoptosis of rat notochordal cells. A regulated negative balance of notochordal cell proliferation against apoptosis is likely to involve the disappearance of notochordal cells in the rat NP. This information on the mechanism for apoptosis of notochordal cells could be important in the investigation of intervertebral disc development as well as aging and perhaps degeneration.

Aging↗
PubMed2004

Signal propagation and failure in discrete autocrine relays.

A mechanistic model of discrete one-dimensional arrays of autocrine cells interacting via diffusible signals is investigated. Under physiologically relevant assumptions, the model is reduced to a system of ordinary differential equations for the intracellular variables, with a particular, biophysically derived type of long-range coupling between cells. Exact discrete traveling wave and static kink solutions are obtained in the model with sharp threshold nonlinearity. It is argued that the considered mechanism may be used extensively for transmission of information in tissues during homeostasis and development.

Autocrine Communication↗
PubMed2004

Heat shock-induced matrix metalloproteinase (MMP)-1 and MMP-3 are mediated through ERK and JNK activation and via an autocrine interleukin-6 loop.

Although many studies have been performed to elucidate the molecular consequences of ultraviolet irradiation, little is known about the effect of infrared radiation on skin aging. In addition to photons, heat is likely to be generated as a consequence of infrared irradiation, and heat shock is widely considered to be an environmental stress. Here we investigated the effect of heat shock on the expressions of matrix metalloproteinase (MMP)-1, MMP-2, and MMP-3 in cultured human skin fibroblasts. Heat shock induced the expression of MMP-1 and MMP-3, but not MMP-2, at the mRNA and protein levels in a temperature-dependent manner, and caused the rapid activation of three distinct mitogen-activated protein kinases (MAPK), extracelluar signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK. The heat shock-induced MMP-1 and MMP-3 expression was suppressed by the inhibition of ERK and JNK but not by p38 MAPK inhibition. Furthermore, heat shock increased the synthesis and release of interleukin-6 (IL-6) into culture media. The specific inhibition of IL-6 using a monoclonal antibody against IL-6 greatly reduced the expression of MMP-1 and MMP-3 induced by heat shock. Taken together, our results suggest that ERK and JNK play an important role in the induction of MMP-1 and MMP-3 by heat shock and that the heat shock-induced expression of MMP-1 and MMP-3 is mediated via an IL-6-dependent autocrine mechanism.

Antibodies↗
PubMed2005

Ultraviolet A-induced signaling involves a ceramide-mediated autocrine loop leading to ceramide de novo synthesis.

Exposure of human keratinocytes to ultraviolet A (UVA) radiation at physiological doses leads to a biphasic activation of transcription factor activator protein-2 (AP-2) and subsequently to a biphasic increase in gene expression of, e.g. intercellular adhesion molecule-1 (ICAM-1). Both kinetics follow a pattern with a first peak between 0.5 and 2 h and a second, more sustained activation between 16 and 48 h. We have previously reported on a non-enzymatic triggering of the ceramide signaling cascade as the initiating step in UVA radiation-induced signaling. In this study, we report that this early (0.5-1 h) peak in ceramide content is followed by a second peak that (i) was associated with an increased expression and activity of serine palmitoyltransferase, the key enzyme of ceramide synthesis, (ii) could be prevented by inhibitors of this enzyme, and (iii) was of functional relevance because its inhibition abrogated the second, but not the first peak in UVA radiation-induced ICAM-1 gene expression. We hypothesize that this second peak most likely resulted from a ceramide-mediated autocrine loop, for (i) inhibition of the first ceramide peak resulted in inhibition of the second peak and (ii) cell-permeable ceramides-induced serine palmitoyltransferase expression, activity, and subsequently ceramide content.

Acyltransferases↗
PubMed2005

In vivo and in vitro evidence for autocrine DCoH/HNF-1alpha transcription of albumin in the human epidermis.

The presence of albumin in the human epidermis has been reported more than a decade ago, but until now, it was assumed that this protein is synthesized in the liver and transported to the avascular skin. To our knowledge, transcription of albumin in the human epidermis was never considered. In this report, we present for the first time evidence for autocrine synthesis of albumin in the human epidermis in keratinocytes in situ and in vitro. Using double immunofluorescence labelling, we identified that albumin colocalized together with its transcription factor PCD/DCoH/HNF-1alpha in suprabasal keratinocytes in human full-thickness skin sections and in keratinocytes cultured in serum-free medium. Moreover, albumin and HNF-1alpha protein expression was confirmed by Western blotting in undifferentiated and differentiated keratinocytes as well as in human epidermal suction blister roof extracts. Reverse-transcriptase polymerase chain reaction analysis from human epidermal keratinocytes and epidermal suction blister roofs revealed the transcription of albumin. Using in vivo fluorescence excitation spectroscopy at the surface of human skin, we confirmed albumin as a major constituent yielding a lambda(max) at 295 nm, which was assigned to the single tryptophan 214 fluorophore in this protein. This in vivo result is in agreement with albumin concentrations of 10(-3) M, underlining the importance of this protein in epidermal homeostasis.

Albumins↗
PubMed2005

Autocrine secretion of osteopontin results in degradation of I kappa B in Bcr-Abl-expressing cells.

Osteopontin has been identified as a marker of metastasis formation and its increased expression has been correlated with the malignancy of cancer. In this study we provide evidence that increased expression of osteopontin may also be associated with progression of Bcr-Abl-expressing leukaemia cells. The Bcr-Abl fusion protein, generated by the Philadelphia translocation, is the hallmark of chronic myeloid leukaemia (CML). CML exhibits clinically distinct phases. Advanced disease shows defective differentiation, bone marrow infiltration and drug resistance. The critical signalling mediating this disease progression is unknown. Increased aggressiveness of the disease has been correlated with elevated amounts of Bcr-Abl. We generated a 32D cell line model to study the consequences of different expression levels of Bcr-Abl. Osteopontin was identified by microarray analysis as highly upregulated in cells expressing elevated amounts of Bcr-Abl. Moreover, in high Bcr-Abl expressing cells, an additional 50 kDa isoform of osteopontin was detected. It was found that this protein was secreted and that myeloid progenitor cells also expressed appropriate receptors for autocrine activation. We demonstrated that secretion of osteopontin resulted in enhanced degradation of I kappa B, the inhibitor of NF-kappa B. These data indicate a novel consequence of elevated Bcr-Abl expression, which may contribute to the progression of CML.

Animals↗
PubMed2006

Expression of autocrine motility factor mRNA is a poor prognostic factor in high-grade astrocytoma.

It has been reported that tumor infiltration is correlated with the expression of autocrine motility factor (AMF) and its receptor 78 kDa glycoprotein (gp78). The purpose of the present study was to detect AMF and gp78 mRNA expression levels and their localization in high-grade astrocytomas (glioblastoma and anaplastic astrocytoma) and to determine whether AMF and gp78 are important prognostic factors. A total of 32 formalin-fixed and paraffin-embedded glioblastomas and 23 formalin-fixed and paraffin-embedded anaplastic astrocytomas was used. The expressions of AMF and gp78 mRNA were detected using the highly sensitive in situ hybridization method. The expression of AMF mRNA was detected in 27 of 32 glioblastomas (84.4%) and 11 of 23 anaplastic astrocytomas (47.8%). The positivity of AMF mRNA was significantly higher in glioblastomas than in anaplastic astrocytomas (P = 0.0094), but gp78 mRNA was detected in most cases and no statistical significance was observed. The overall survival of patients with AMF expression was significantly shorter than patients without AMF expression (P = 0.0175). In anaplastic astrocytomas, the overall survival of patients with AMF expression was also significantly shorter than in patients without AMF expression (P = 0.0058). This study demonstrated that AMF is a poor prognostic factor in high-grade astrocytomas.

Adult↗
PubMed2001

Release of ATP by a human retinal pigment epithelial cell line: potential for autocrine stimulation through subretinal space.

1. Stimulation of purinergic receptors on retinal pigment epithelial (RPE) cells can increase the rate of fluid transport or decrease phagocytosis. This study aims to: determine whether the purine ATP can be released from RPE cells, begin probing the mechanism of any release and test whether cells degrade ATP extracellularly. 2. ATP release was monitored from cultured human ARPE-19 cells with the luciferin-luciferase assay. Biphasic release of ATP was triggered by basic fibroblast growth factor (bFGF), by the pyrimidine uridine triphosphate (UTP) and by hypotonicity. 3. The Cl(-) channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) inhibited release of ATP, suggesting that release was associated with Cl(-) channels. 4. Elevating intracellular Ca(2+) directly with ionomycin was insufficient to trigger ATP release. 5. UTP induced a biphasic elevation in intracellular Ca(2+). NPPB inhibited the second phase, suggesting autostimulation by released ATP. 6. Cells grown on permeable supports showed apical release of ATP, analogous to release into subretinal space in vivo. 7. The presence of ecto-ATPases on ARPE-19 cell membranes was suggested by the degradation of ATP added to intact cells. 8. Phagocytosis of fluorescent beads was inhibited by ATP, but the ecto-5'-nucleotidase inhibitor alpha, beta-methylene ADP prevented this, suggesting that inhibition was mediated by extracellular conversion of ATP to adenosine. 9. These results suggest that growth factors, pyrimidines and changes in tonicity could trigger ATP release into subretinal space. The levels of ATP released may be capable of autocrine stimulation of ATP receptors, while conversion to adenosine by ecto-enzymes could alter phagocytosis.

Adenosine Triphosphate↗
PubMed2004

Beta-naphthoflavone disturbs astrocytic differentiation of C6 glioma cells by inhibiting autocrine interleukin-6.

Regulation of astrocyte differentiation is a key process in the development of the central nervous system (CNS), and disturbance of the differentiation can lead to brain system dysfunction. Here we show that beta-naphthoflavone (betaNF), an agonist of the aryl hydrocarbon receptor (AhR), disturbed the cAMP-induced astrocytic differentiation of C6 glioma by inhibiting autocrine interleukin-6 (IL-6). Treatment of cells with betaNF reduced the induction of an astrocyte marker glial fibrillary acidic protein (GFAP). This was caused by the inactivation of its upstream transcription factor signal transducer and activator of transcription 3 (STAT3) by betaNF. In addition, betaNF attenuated the induction of the IL-6 gene, which leads to the activation of STAT3. Most importantly, the inhibitory effect of betaNF on GFAP promoter activity was recovered by the addition of recombinant IL-6. Taken together, these results indicate that the inhibitory effect of betaNF on IL-6 induction suppresses STAT3 activation. These processes subsequently lead to the attenuation of GFAP induction.

Animals↗
PubMed2005

The excitoprotective effect of N-methyl-D-aspartate receptors is mediated by a brain-derived neurotrophic factor autocrine loop in cultured hippocampal neurons.

The neuroprotective effect and molecular mechanisms underlying preconditioning with N-methyl-D-aspartate (NMDA) in cultured hippocampal neurons have not been described. Pre-incubation with subtoxic concentrations of the endogenous neurotransmitter glutamate protects vulnerable neurons against NMDA receptor-mediated excitotoxicity. As a result of physiological preconditioning, NMDA significantly antagonizes the neurotoxicity resulting from subsequent exposure to an excitotoxic concentration of glutamate. The protective effect of glutamate or NMDA is time- and concentration-dependent, suggesting that sufficient agonist and time are required to establish an intracellular neuroprotective state. In these cells, the TrkB ligand, brain-derived neurotrophic factor (BDNF) attenuates glutamate toxicity. Therefore, we tested the hypothesis that NMDA protects neurons via a BDNF-dependent mechanism. Exposure of hippocampal cultures to a neuroprotective concentration of NMDA (50 microM) evoked the release of BDNF within 2 min without attendant changes in BDNF protein or gene expression. The accumulated increase of BDNF in the medium is followed by an increase in the phosphorylation (activation) of TrkB receptors and a later increase in exon 4-specific BDNF mRNA. The neuroprotective effect of NMDA was attenuated by pre-incubation with a BDNF-blocking antibody and TrkB-IgG, a fusion protein known to inhibit the activity of extracellular BDNF, suggesting that BDNF plays a major role in NMDA-mediated survival. These results demonstrate that low level stimulation of NMDA receptors protect neurons against glutamate excitotoxicity via a BDNF autocrine loop in hippocampal neurons and suggest that activation of neurotrophin signaling pathways plays a key role in the neuroprotection of NMDA.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2005

Autocrine activation of EGF receptor promotes oscillation of glutamate-induced calcium increase in astrocytes cultured in rat cerebral cortex.

We previously reported that astrocytes cultured for more than 2 days in a defined medium containing epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) showed calcium oscillation in response to glutamate, whereas the response pattern was transient in the absence of the exogenous growth factors. In the present study, we found that astrocytes showed glutamate-induced calcium oscillation, even in growth factor-free medium, if the cells had been cultured for more than 5 days. The calcium oscillation promoted by the prolonged culture period was suppressed by an inhibitor of EGF receptor tyrosine kinase, but not by a neutralizing antibody to bFGF, indicating that the accumulation of an autocrine factor that activates the EGF receptor leads to calcium oscillation. Astrocytes in our culture system expressed EGF, transforming growth factor alpha (TGFalpha), bFGF and acidic fibroblast growth factor (aFGF). Exogenous aFGF, which induced astrocyte immediate early gene expression to the same extent as EGF or bFGF, did not affect calcium oscillation. Exogenous EGF and bFGF promoted astrocyte hypertrophic morphology and proliferation, as well as calcium oscillation. In contrast, these properties did not accompany calcium oscillation induced by the prolonged culture period. These results suggest that astrocytes possess the ability to promote their own calcium oscillation, which is independent of hypertrophic changes to reactive astrocytes.

Animals↗
PubMed2005

Secretion of brain-derived neurotrophic factor from PC12 cells in response to oxidative stress requires autocrine dopamine signaling.

Expression of brain-derived neurotrophic factor (BDNF) is sensitive to changes in oxygen availability, suggesting that BDNF may be involved in adaptive responses to oxidative stress. However, it is unknown whether or not oxidative stress actually increases availability of BDNF by stimulating BDNF secretion. To approach this issue we examined BDNF release from PC12 cells, a well-established model of neurosecretion, in response to hypoxic stimuli. BDNF secretion from neuronally differentiated PC12 cells was strongly stimulated by exposure to intermittent hypoxia (IH). This response was inhibited by N-acetyl-l-cysteine, a potent scavenger of reactive oxygen species (ROS) and mimicked by exogenous ROS. IH-induced BDNF release requires activation of tetrodotoxin sensitive Na+ channels and Ca2+ influx through N- and L-type channels, as well as mobilization of internal Ca2+ stores. These results demonstrate that oxidative stress can stimulate BDNF release and that underlying mechanisms are similar to those previously described for activity-dependent BDNF secretion from neurons. Surprisingly, we also found that IH-induced secretion of BDNF was blocked by dopamine D2 receptor antagonists or by inhibition of dopamine synthesis with alpha-methyl-p-tyrosine. These data indicate that oxidative stress can stimulate BDNF release through an autocrine or paracrine loop that requires dopamine receptor activation.

Animals↗
PubMed2000

Autocrine effects of nitric oxide on HCO(3)(-) transport by rat thick ascending limb.

BACKGROUND: In vivo and in vitro studies have shown that nitric oxide (NO) is an important modulator of transport processes along the nephron. The thick ascending limb (TAL) plays a significant role in the urine-concentrating mechanism and in the maintenance of acid/base balance. METHODS: TALs from male Sprague-Dawley rats were isolated and perfused, and net bicarbonate flux (J(HCO3)(-) was determined. RESULTS: In perfused TALs, 0.5 mmol/L L-arginine (L-Arg), the substrate for NO synthase, significantly lowered J(HCO3)(-) from 35.4 +/- 4.6 to 23.2 +/- 2.9 pmol. mm(-1). min(-1), a decrease of 36.9 +/- 11.6% (P < 0.025). D-Arg (0.5 mmol/L) had no effect on J(HCO3)(-) (N = 7). In the presence of 5 mmol/L L-NAME, an NO synthase (NOS) inhibitor, the addition of L-Arg did not affect TAL J(HCO3)(-) (43.4 +/- 4.4 vs. 44.6 +/- 5.0 pmol. mm(-1). min(-1)). L-NAME alone (5 mmol/L) did not affect TAL J(HCO3)(-). After removing L-Arg from the bath, J(HCO3)(-) increased from 26.2 +/- 3.9 to 34.8 +/- 3.2 pmol. mm(-1). min(-1) (P < 0.01), indicating no cytotoxicity of NO. We next investigated the effect of cGMP analogues on TAL J(HCO3)(-). 8-Br-cGMP (50 micromol/L) and db-cGMP (50 micromol/L) significantly decreased J(HCO3)(-) by 26.3 +/- 9.1% and 35.1 +/- 11.6%, respectively. In the presence of cGMP (50 micromol/L), the addition of L-Arg had no effect on J(HCO3)(-). In the presence of KT-5823 (2 mircromol/L), a protein kinase G inhibitor, the addition of L-Arg did not change TAL J(HCO3)(-) (N = 5). CONCLUSIONS: We conclude that (1) endogenously produced NO inhibits TAL J(HCO3)(-) in an autocrine manner, (2) cGMP mediates all the effects of NO, and (3) this effect is mediated by protein kinase G activation.

Alkaloids↗