Biomedical subjects

C Sumners

Publications and source records attributed to C Sumners.

At least 19 recordsLinked to original sources

PubMed2001

Oxygen and glucose deprivation-induced neuronal apoptosis is attenuated by halothane and isoflurane.

UNLABELLED: Both in vitro and in vivo evidence supports the reduction of early ischemic, both global and focal, brain injury by volatile anesthetics. However, the protection afforded by volatile anesthetics in later neuronal death, i.e., apoptosis, caused by global ischemia has not been investigated. We induced oxygen and glucose deprivation in neuronal cortical cell cultures prepared from newborn rats on in vitro Days 10-14. This hypoxic (PO2 <50 mm Hg) condition was maintained continuously (30, 60, and 90 min). In a separate experiment, the neuronal cell cultures were exposed to isoflurane (1.13%, 2.3%, or 3.3%) or halothane (1.7%, 3.4%, or 5.1%) before oxygen and glucose deprivation, with continued exposure to isoflurane or halothane during oxygen and glucose deprivation. After 48 h, neuronal apoptosis was assessed with terminal deoxynucleotidyl transferase-mediated in situ nick-end labeling and DNA gel electrophoresis. Oxygen and glucose deprivation (30, 60, and 90 min) caused significant apoptosis of cerebral cortical cultured neurons. However, pretreatment and continued treatment during the period of oxygen and glucose deprivation with halothane or isoflurane resulted in a concentration-dependent attenuation of oxygen and glucose deprivation-induced neuronal apoptosis. IMPLICATIONS: This is the first investigation to evaluate the effect of volatile anesthetics on oxygen and glucose deprivation-induced neuronal apoptosis. Oxygen and glucose deprivation-induced neuronal apoptosis can be decreased by prior and continued administration of halothane or isoflurane.

Anesthetics, Inhalation↗

PubMed2001

ANG II-mediated inhibition of neuronal delayed rectifier K+ current: role of protein kinase C-alpha.

It was previously determined that ANG II and phorbol esters inhibit Kv current in neurons cultured from newborn rat hypothalamus and brain stem in a protein kinase C (PKC)- and Ca2+-dependent manner. Here, we have further defined this signaling pathway by investigating the roles of "physiological" activators of PKC and different PKC isozymes. The cell-permeable PKC activators, diacylglycerol (DAG) analogs 1,2-dioctanoyl-sn-glycerol (1 micromol/l, n = 7) and 1-oleoyl-2-acetyl-sn-glycerol (1 micromol/l, n = 6), mimicked the effect of ANG II and inhibited Kv current. These effects were abolished by the PKC inhibitor chelerythrine (1 micromol/l, n = 5) or by chelation of internal Ca2+ (n = 8). PKC antisense (AS) oligodeoxynucleotides (2 micromol/l) against Ca2+-dependent PKC isoforms were applied to the neurons to manipulate the endogenous levels of PKC. PKC-alpha-AS (n = 4) treatment abolished the inhibitory effects of ANG II and 1-oleoyl-2-acetyl-sn-glycerol on Kv current, whereas PKC-beta-AS (n = 4) and PKC-gamma-AS (n = 4) did not. These results suggest that the angiotensin type 1 receptor-mediated effects of ANG II on neuronal Kv current involve activation of PKC-alpha.

Alkaloids↗

PubMed2001

Chronotropic effect of angiotensin II via type 2 receptors in rat brain neurons.

Previously, we determined that angiotensin II (Ang II) elicits an Ang II type 2 (AT(2)) receptor-mediated increase of neuronal delayed rectifier K(+) (I(KV)) current in neuronal cultures from newborn rat hypothalamus and brain stem. This requires generation of lipoxygenase (LO) metabolites of arachidonic acid (AA) and activation of serine/threonine phosphatase type 2A (PP-2A). Enhancement of I(KV) results in a decrease in net inward current during the action potential (AP) upstroke as well as shortening of the refractory period, which may lead to alterations in neuronal firing rate. Thus, in the present study, we used whole-cell current clamp recording methods to investigate the AT(2) receptor-mediated effects of Ang II on the firing rate of cultured neurons from the hypothalamus and brain stem. At room temperature, these neurons exhibited spontaneous APs with an amplitude of 77.72 +/- 2.7 mV (n = 20) and they fired at a frequency of 0.8 +/- 0.1 Hz (n = 11). Most cells had a prolonged early after-depolarization that followed an initial fully developed AP. Superfusion of Ang II (100 nM) plus losartan (LOS, 1 microM) to block Ang II type 1 receptors elicited a significant chronotropic effect that was reversed by the AT(2) receptor inhibitor PD 123,319 (1 microM). LOS alone had no effect on any of the parameters measured. The chronotropic effect of Ang II was reversed by the general LO inhibitor 5,8,11,14-eicosatetraynoic acid (10 microM) or by the selective PP-2A inhibitor okadaic acid (1 nM) and was mimicked by the 12-LO metabolite of AA 12-(S)-hydroxy-(5Z, 8Z, 10E, 14Z)-eicosatetraynoic acid. These data indicate that Ang II elicits an AT(2) receptor-mediated increase in neuronal firing rate, an effect that involves generation of LO metabolites of AA and activation of PP-2A.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗

PubMed2001

Novel role of macrophage migration inhibitory factor in angiotensin II regulation of neuromodulation in rat brain.

Previously we determined that angiotensin II (Ang II) activates neuronal AT(1) receptors, located in the hypothalamus and the brainstem, to stimulate noradrenergic pathways. To link Ang II to the regulation of norepinephrine metabolism in neurons cultured from newborn rat hypothalamus and brainstem we have used cDNA arrays for high throughput gene expression profiling. Of several genes that were regulated, we focused on macrophage migration inhibitory factor (MIF), which has been associated with the modulation of norepinephrine metabolism. In the presence of the selective AT(2) receptor antagonist PD123,319 (10 microM), incubation of cultures with Ang II (100 nM; 1-24 h) elicited an increase in MIF gene expression. Western immunoblots further revealed that Ang II (100 nM; 1-24 h) increased neuronal MIF protein expression. This effect was inhibited by the AT(1) receptor antagonist losartan (10 microM), the PLC inhibitor U-73122 (10 or 25 microM), the PKC inhibitor chelerythrine (10 microM), and the Ca(2+) chelator 1,2-bis-[2-aminophenoxy]-ethane-N,N,N',N'-tetraacetic acid tetrakis acetoxymethyl ester (10 microM). Taken together with our observation that MIF is expressed in the terminal fields of noradrenergic neurons (hypothalamus) and that Ang II increases the expression of MIF in this region in vivo, our data may suggest a novel role of Ang II in norepinephrine metabolism.

Angiotensin II↗

PubMed2001

Gene expression profiling of rat brain neurons reveals angiotensin II-induced regulation of calmodulin and synapsin I: possible role in neuromodulation.

Angiotensin (Ang II) activates neuronal AT(1) receptors located in the hypothalamus and the brainstem and stimulates noradrenergic neurons that are involved in the control of blood pressure and fluid intake. In this study we used complementary DNA microarrays for high throughput gene expression profiling to reveal unique genes that are linked to the neuromodulatory actions of Ang II in neuronal cultures from newborn rat hypothalamus and brainstem. Of several genes that were regulated, we focused on calmodulin and synapsin I. Ang II (100 nM; 1-24 h) elicited respective increases and decreases in the levels of calmodulin and synapsin I messenger RNAs, effects mediated by AT(1) receptors. This was associated with similar changes in calmodulin and synapsin protein expression. The actions of Ang II on calmodulin expression involve an intracellular pathway that includes activation of phospholipase C, increased intracellular calcium, and stimulation of protein kinase C. Taken together with studies that link calmodulin and synapsin I to axonal transport and exocytotic processes, the data suggest that Ang II regulates these two proteins via a Ca(2+)-dependent pathway, and that this may contribute to longer term or slower neuromodulatory actions of this peptide.

Angiotensin II↗

PubMed2000

Antagonism of the positive dromotropic effect of isoproterenol by adenosine: role of nitric oxide, cGMP-dependent cAMP-phosphodiesterase and protein kinase G.

We hypothesized that nitric oxide (NO) plays an important role in mediating the anti-adrenergic effect of adenosine on atrioventricular (AV) nodal conduction. In guinea-pig hearts instrumented for measurement of AV nodal conduction time (atrium-to-His bundle, A-H, interval), the NO synthase (NOS) inhibitor, l-NMMA (100 microm), reversibly inhibited 80% (P=0.009, n=6) of adenosine's anti-adrenergic action on the positive dromotropic effect of isoproterenol (0.01 microm). In parallel studies carried out in rabbit AV nodal myocytes, intracellular mechanisms whereby NO mediates the inhibitory effect of adenosine on isoproterenol-induced A-H interval shortening were studied. Adenosine (3 microm) inhibited isoproterenol-stimulated (0.1 microm) I(Ca,L)(beta -I(Ca,L)) by 46+/-6% (P<0.001, n=17). Consistent with isolated heart data, the NOS inhibitors, l -NMMA (100 microm) and L-NNA (500 microm) attenuated the effect of adenosine on beta -I(Ca,L)by 69+/-8% (P<0.001, n=16) and 69+/-7% (P<0.001, n=10), respectively. An inhibitor of NO-stimulated guanylyl cyclase LY83538 (40 microm) reduced the inhibitory effect of adenosine on beta -I(Ca,L)by 97+/-6% (P=0.004, n=15). Similarly, the non-specific inhibitor of cAMP-phosphodiesterases IBMX (50 microm) decreased the anti-adrenergic effect of adenosine by 60% (P=0.02, n=6), whereas the extracellular application of the non-hydrolyzeable cAMP analog 8-Br-cAMP (500 microm) prevented this action of adenosine. Activation of cGMP-dependent protein kinase (PKG) by CPT-cGMP (300 microm) diminished beta -I(Ca,L), but to a significantly smaller degree (16+/-4%, P=0.025, n=12) than that caused by adenosine. NO mediates the anti-adrenergic effect of adenosine on AV nodal conduction by a mechanism predominately involving activation of cGMP-dependent cAMP-phosphodiesterase and to a lesser extent activation of PKG.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed2000

Expression of angiotensin AT(1) and AT(2) receptors in adult rat cardiomyocytes after myocardial infarction. A single-cell reverse transcriptase-polymerase chain reaction study.

The effector hormone of the renin-angiotensin system, angiotensin II, plays a major role in cardiovascular regulation. In rats, both angiotensin receptor subtypes, AT(1) and AT(2), are up-regulated after myocardial infarction but previous studies failed to identify the cell types which express the AT(2) receptor in the heart. To address this question we established a single-cell reverse transcriptase-polymerase chain reaction for AT(1) and AT(2) receptors to determine whether these receptor subtypes are expressed in adult rat cardiomyocytes before and 1 day after myocardial infarction. By laser-assisted cell picking, section profiles of single cells without genomic DNA contamination were isolated. After dividing samples into two identical aliquots, polymerase chain reaction amplification for AT(1) and AT(2) receptors was carried out and polymerase chain reaction products were subjected to gel electrophoresis. Compared to control (n = 4) and sham-operated animals (n = 4), the number of cardiomyocytes expressing the AT(1) receptor mRNA 1 day after myocardial infarction (n = 4) was not changed (42% and 33% versus 45%, respectively). On the other hand, AT(2) receptor mRNA was expressed in 8% and 13%, respectively, of cardiomyocytes gained from control (n = 4) and sham-operated animals (n = 4) and in 14% isolated after myocardial infarction (n = 4). These results demonstrate for the first time that the AT(2) receptor is expressed in adult cardiomyocytes in vivo. They further suggest that the previously observed up-regulation of cardiac AT(1) and AT(2) receptors after myocardial infarction involves cell types other than cardiomyocytes.

Animals↗

PubMed2000

Angiotensin II-induced decrease in expression of inducible nitric oxide synthase in rat astroglial cultures: role of protein kinase C.

Inducible nitric oxide synthase (iNOS) has been implicated as a mediator of cellular toxicity in a variety of neurodegenerative disorders. Nitric oxide, which is generated in high quantities following induction of iNOS, combines with other oxygen radicals to form highly reactive, death-inducing compounds. Given the frequency of neuronal death due to neurodegenerative diseases, cerebral trauma, and stroke, it is important to study the mechanisms of regulation of iNOS in the brain. We demonstrated previously that angiotensin II (Ang II) decreases the expression of iNOS produced by bacterial endotoxin or cytokines in cultured astroglia prepared from adult rat brain. Here, we have addressed the mechanisms by which Ang II negatively modulates iNOS. The inhibitory effects of Ang II on lipopolysaccharide-induced expression of iNOS mRNA and protein and nitrite accumulation were mimicked by the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate. Down-regulation of PKC produced by long-term treatment of astroglia with phorbol 12-myristate 13-acetate abolished the inhibitory effect of Ang II on lipopolysaccharide-stimulated expression of iNOS mRNA and nitrite accumulation. Finally, the reduction of lipopolysaccharide-induced nitrite accumulation by Ang II was attenuated by the selective PKC inhibitor chelerythrine. Collectively, these data indicate a role for PKC in the inhibitory actions of Ang II on iNOS expression in cultured astroglia.

Angiotensin II↗

PubMed2000

The angiotensin II type 2 receptor: an enigma with multiple variations.

Since it was discovered ten years ago, the angiotensin II (ANG II) type 2 (AT(2)) receptor has been an enigma. This receptor binds ANG II with a high affinity but is not responsible for mediating any of the classical physiological actions of this peptide, all of which involve the ANG II type 1 (AT(1)) receptor. Furthermore, the AT(2) receptor exhibits dramatic differences in biochemical and functional properties and in patterns of expression compared with the AT(1) receptor. During the past decade, much information has been gathered about the AT(2) receptor, and the steadily increasing number of publications indicates a growing interest in this new and independent area of research. A number of studies suggest a role of AT(2) receptors in brain, renal, and cardiovascular functions and in the processes of apoptosis and tissue regeneration. Despite these advances, nothing stands out as the major singular function of these receptors. The study of AT(2) receptors has reached a crossroads, and innovative approaches must be considered so that unifying mechanisms as to the function of these unique receptors can be put forward. In this review we will discuss the advances that have been made in understanding the biology of the AT(2) receptor. Furthermore, we will consider how these discoveries, along with newer experimental approaches, may eventually lead to the elusive physiological and pathophysiological functions of these receptors.

Animals↗

PubMed2000

Angiotensin II increases neuronal delayed rectifier K(+) current: role of 12-lipoxygenase metabolites of arachidonic acid.

Angiotensin II (Ang II) elicits an Ang II type 2 (AT(2)) receptor-mediated increase in voltage-dependent delayed rectifier K(+) current (I(KV)) in neurons cultured from newborn rat hypothalamus and brain stem. In previous studies, we have determined that this effect of Ang II is mediated via a Gi protein, activation of phospholipase A(2) (PLA(2)), and generation of arachidonic acid (AA). AA is rapidly metabolized within cells via lipoxygenases (LO), cyclooxygenase (COX) or p450 monooxygenase enzymes, and the metabolic products are known regulators of K(+) currents and channels. Thus in the present study, we have investigated whether the AT(2) receptor-mediated effects of Ang II on neuronal I(KV) require AA metabolism and if so, which metabolic pathways are involved. The data presented here indicate that the stimulatory actions of Ang II and AA on neuronal I(KV) are attenuated by selective blockade of 12-LO enzymes. However, the effects of Ang II are not altered by blockade of 5-LO or p450 monooxygenase enzymes. Furthermore, the actions of Ang II are mimicked by a 12-LO metabolite of AA, but 5-LO metabolites such as leukotriene B(4) and C(4) do not alter neuronal I(KV). These data indicate that the AT(2) receptor-mediated stimulation of neuronal I(KV) is partially mediated through 12-LO metabolites of AA.

5,8,11,14-Eicosatetraynoic Acid↗

PubMed1999

Enhanced transgene expression in rat brain cell cultures with a disulfide-containing cationic lipid.

The transfection efficiency of a disulfide-containing cationic lipid, 1',2' dioleoyl-sn-glycero-3'-succinyl-2-hydroxyethyl disulfide ornithine conjugate (DOGSDSO) and its non-disulfide analog (DOGSHDO) were compared in neuronal, astroglial and microglial cultures from newborn rat cerebral cortex. We hypothesized that the relatively high intracellular concentrations of reductive substances in the cytoplasm may help to cleave the reversible disulfide bond in DOGSDSO, thus increasing free DNA and decreasing toxicity due to rapid degradation of the lipid. We have demonstrated through mass spectrometric analysis that a reductive compound, e.g. dithiothreitol (DTT) could degrade the disulfide lipid. DOGSDSO was more efficient at transfecting each type of brain cell than were the non-disulfide DOGSHDO and DOTAP (1,2-dioleoyl-3-trimethyl-ammonium-propane) liposomes. These results demonstrate that disulfide-containing cationic liposomes facilitate gene transfection in cultured rat brain cells.

Animals↗

PubMed1999

Angiotensin II type 1 receptor-mediated inhibition of K+ channel subunit kv2.2 in brain stem and hypothalamic neurons.

Angiotensin II (Ang II) has powerful modulatory actions on cardiovascular function that are mediated by specific receptors located on neurons within the hypothalamus and brain stem. Incubation of neuronal cocultures of rat hypothalamus and brain stem with Ang II elicits an Ang II type 1 (AT1) receptor-mediated inhibition of total outward K+ current that contributes to an increase in neuronal firing rate. However, the exact K+ conductance(s) that is inhibited by Ang II are not established. Pharmacological manipulation of total neuronal outward K+ current revealed a component of K+ current sensitive to quinine, tetraethylammonium, and 4-aminopyridine, with IC50 values of 21.7 micromol/L, 1.49 mmol/L, and 890 micromol/L, respectively, and insensitive to alpha-dendrotoxin (100 to 500 nmol/L), charybdotoxin (100 to 500 nmol/L), and mast cell degranulating peptide (1 micromol/L). Collectively, these data suggest the presence of Kv2.2 and Kv3.1b. Biophysical examination of the quinine-sensitive neuronal K+ current demonstrated a macroscopic conductance with similar biophysical properties to those of Kv2.2 and Kv3.1b. Ang II (100 nmol/L), in the presence of the AT2 receptor blocker PD123,319, elicited an inhibition of neuronal K+ current that was abolished by quinine (50 micromol/L). Reverse transcriptase-polymerase chain reaction analysis confirmed the presence of Kv2.2 and Kv3.1b mRNA in these neurons. However, Western blot analyses demonstrated that only Kv2.2 protein was present. Coexpression of Kv2.2 and the AT1 receptor in Xenopus oocytes demonstrated an Ang II-induced inhibition of Kv2.2 current. Therefore, these data suggest that inhibition of Kv2.2 contributes to the AT1 receptor-mediated reduction of neuronal K+ current and subsequently to the modulation of cardiovascular function.

Angiotensin II↗

PubMed1999

Angiotensin II type 1 receptor-modulated signaling pathways in neurons.

Mammalian brain contains high densities of angiotensin II (Ang II) type 1 (AT1) receptors, localized mainly to specific nuclei within the hypothalamus and brainstem regions. Neuronal AT1 receptors within these areas mediate the stimulatory actions of central Ang II on blood pressure, water and sodium intake, and vasopressin secretion, effects that involve the modulation of brain noradrenergic pathways. This review focuses on the intracellular events that mediate the functional effects of Ang II in neurons, via AT1 receptors. The signaling pathways involved in short-term changes in neuronal activity, membrane ionic currents, norepinephrine (NE) release, and longer-term neuromodulatory actions of Ang II are discussed. It will be apparent from this discussion that the signaling pathways involved in these events are often distinct.

Angiotensin II↗

PubMed1999

Angiotensin II decreases neuronal delayed rectifier potassium current: role of calcium/calmodulin-dependent protein kinase II.

Angiotensin II (Ang II) acts at specific receptors located on neurons in the hypothalamus and brain stem to elicit alterations in blood pressure, fluid intake, and hormone secretion. These actions of Ang II are mediated via Ang II type 1 (AT1) receptors and involve modulation of membrane ionic currents and neuronal activity. In previous studies we utilized neurons cultured from the hypothalamus and brain stem of newborn rats to investigate the AT1 receptor-mediated effects of Ang II on neuronal K+ currents. Our data indicate that Ang II decreases neuronal delayed rectifier (Kv) current, and that this effect is partially due to activation of protein kinase C (PKC), specifically PKCalpha. However, the data also indicated that another Ca2+-dependent mechanism was also involved in addition to PKC. Because Ca2+/calmodulin-dependent protein kinase II (CaM KII) is a known modulator of K+ currents in neurons, we investigated the role of this enzyme in the AT1 receptor-mediated reduction of neuronal Kv current by Ang II. The reduction of neuronal Kv current by Ang II was attenuated by selective inhibition of either calmodulin or CaM KII and was mimicked by intracellular application of activated (autothiophosphorylated) CaM KIIalpha. Concurrent inhibition of CaM KII and PKC completely abolished the reduction of neuronal Kv by Ang II. Consistent with these findings is the demonstration that Ang II increases CaM KII activity in neuronal cultures, as evidenced by increased levels of autophosphorylated CaM KIIalpha subunit. Last, single-cell reverse transcriptase (RT)-PCR analysis revealed the presence of AT1 receptor-, CaM KIIalpha-, and PKCalpha subunit mRNAs in neurons that responded to Ang II with a decrease in Kv current. The present data indicate that the AT1 receptor-mediated reduction of neuronal Kv current by Ang II involves a Ca2+/calmodulin/CaM KII pathway, in addition to the previously documented involvement of PKC.

Angiotensin II↗

PubMed1999

Angiotensin II type 2 receptor-mediated apoptosis of cultured neurons from newborn rat brain.

Angiotensin II (Ang II) type 2 (AT2) receptors are highly expressed in neonate brain and may have a role in developmental processes such as apoptosis. Concurrent activation of c-Jun N-terminal kinase (JNK) and inhibition of Erk mitogen-activated protein kinase activities is important for apoptosis in many cells, and we previously demonstrated that stimulation of AT2 receptors causes decreased mitogen-activated protein kinase activity in neurons cultured from newborn rat hypothalamus and brain stem. Using such cultures we have employed terminal deoxynucleotidyl transferase-mediated deoxy-UTP nick end labeling and internucleosomal DNA fragmentation to assess the role of AT2 receptors in neuronal apoptosis. Ang II (100 nM; 4-72 h) alone produced no significant neuronal apoptosis, and AT2 receptor activation did not stimulate JNK activity. However, exposure of cultures to UV radiation (6 J/m2/sec for 4 sec) to stimulate JNK elicited neuronal apoptosis that was significantly enhanced by Ang II, an effect that was abolished by the AT2 receptor antagonist PD 123,319 (1 microM) or the serine/threonine phosphatase inhibitor okadaic acid (3 nM). Additionally, Ang II enhanced the UV radiation-induced decrease in the levels of the DNA repair enzyme poly-(ADP-ribose) polymerase. These data indicate that Ang II, via AT2 receptors and activation of a serine/threonine phosphatase, contributes to neuronal apoptosis.

Angiotensin II↗

PubMed1998

Angiotensin II in central nervous system physiology.

In summary, the prevailing concept is that brain Ang II increases blood pressure by activating AT1 receptors, and that these have a neuromodulating effect to increase the activity of autonomic nervous system. Pathways for Ang II stimulating thirst and blood pressure, increased vasopressin release and sympathetic activation have been outlined. Brain RAS synthesis, while incompletely understood, is active in the absence of a peripheral RAS. Angiotensin elicits specific receptor mediated signals in neurons, particularly in the hypothalamus and brainstem. These actions are due to neuronal membrane ionic currents and the regulation of transcription factors. The areas to be explored further are characterization and functional roles of the other AT receptor subtypes, such as AT4, AT(1-7) and nuclear AT-R. Their interactions with other peptides and transmitters, and their signaling pathways need to be investigated. The story that began 100 years ago with renin is certainly not ended and will continue to unfold as further investigations with new techniques progress.

Angiotensin II↗

PubMed1998

Angiotensin receptors and norepinephrine neuromodulation: implications of functional coupling.

The objective of this review is to examine the role of neuronal angiotensin II (Ang II) receptors in vitro. Two types of G protein-coupled Ang II receptors have been identified in cardiovascularly relevant areas of the brain: the AT1 and the AT2. We have utilized neurons in culture to study the signaling mechanisms of AT1 and AT2 receptors. Neuronal AT1 receptors are involved in norepinephrine (NE) neuromodulation. NE neuromodulation can be either evoked or enhanced. Evoked NE neuromodulation involves AT1 receptor-mediated, losartan-dependent, rapid NE release, inhibition of K+ channels and stimulation of Ca2+ channels. AT1 receptor-mediated enhanced NE neuromodulation involves the Ras-Raf-MAP kinase cascade and ultimately leads to an increase in NE transporter, tyrosine hydroxylase and dopamine beta-hydroxylase mRNA transcription. Neuronal AT2 receptors signal via a Gi protein and are coupled to activation of PP2A and PLA2 and stimulation of K+ channels. Finally, putative cross-talk pathways between AT1 and AT2 receptors will be discussed.

Animals↗

PubMed1998

Angiotensin II type 2 receptor stimulation of neuronal delayed-rectifier potassium current involves phospholipase A2 and arachidonic acid.

Angiotensin II (Ang II) elicits an Ang II type 2 (AT2) receptor-mediated increase in delayed-rectifier K+ current (IK) in neurons cultured from newborn rat hypothalamus and brainstem. This effect involves a pertussis toxin (PTX)-sensitive Gi protein and is abolished by inhibition of serine and threonine phosphatase 2A (PP-2A). Here, we determined that Ang II stimulates [3H]arachidonic acid (AA) release from cultured neurons via AT2 receptors. This effect of Ang II was blocked by inhibition of phospholipase A2 (PLA2) and by PTX. Because AA and its metabolites are powerful modulators of neuronal K+ currents, we investigated the involvement of PLA2 and AA in the AT2 receptor-mediated stimulation of IK by Ang II. Single-cell reverse transcriptase (RT)-PCR analyses revealed the presence of PLA2 mRNA in neurons that responded to Ang II with an increase in IK. The stimulation of neuronal IK by Ang II was attenuated by selective inhibitors of PLA2 and was mimicked by application of AA to neurons. Inhibition of lipoxygenase (LO) enzymes significantly reduced both Ang II- and AA-stimulated IK, and the 12-LO metabolite of AA 12S-hydroxyeicosatetraenoic acid (12S-HETE) stimulated IK. These data indicate the involvement of a PLA2, AA, and LO metabolite intracellular pathway in the AT2 receptor-mediated stimulation of neuronal IK by Ang II. Furthermore, the demonstration that inhibition of PP-2A abolished the stimulatory effects of Ang II, AA, and 12S-HETE on neuronal IK but did not alter Ang II-stimulated [3H]-AA release suggests that PP-2A is a distal event in this pathway.

Angiotensin II↗