Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0043167 (pertussis)
 19,595 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

As a target site for angiotensin II (A-II), renal proximal tubule is unique in that it may be equipped with a local A-II generating system and that both basolateral and apical membranes may be accessible for A-II's action. We have recently conducted studies to examine these possibilities. With in vitro cultured proximal tubular cells, we have demonstrated de novo synthesis of angiotensinogen and renin. With isolated renal brush border membrane (BBM), we have confirmed the presence of A-II receptors and found that A-II directly stimulated BBM Na(+)-H+ exchange. In search of the signal transduction mechanism, we have found that A-II also activated BBM phospholipase A2 (PLA) and that BBM contained a pertussis toxin-sensitive guanine nucleotide binding protein (G-protein) which mediates the effects of A-II. Further studies showed that prevention of PLA activation abolished A-II's effect on Na(+)-H+ exchange, and that activation of PLA by mellitin and addition of arachidonic acid similarly enhanced Na(+)-H+ exchange activity, suggesting that PLA activation may mediate the stimulatory effect of A-II on Na(+)-H+ exchange. These results thus indicate that a local signal transduction mechanism involving G-protein mediated PLA activation exists in renal BBM which mediates A-II's effect on Na(+)-H+ exchange. Taken together, we propose that, independent of A-II in the circulation, local luminal A-II may serve as an important regulatory system on sodium transport in renal proximal tubule.
 ...
PMID:Angiotensin II and proximal tubule sodium transport. 170 7

The alpha subunits of the heterotrimeric guanine nucleotide-binding proteins Gi1, Gi2, Gi3, G0, and Gs have been overexpressed in Sf9 cells using a baculovirus expression system. The Gi1 alpha, Gi2 alpha, Gi3 alpha, and G0 alpha have been purified to homogeneity from infected Spodoptera frugiperda (SF9) cells and characterized. Yields of up to 1.8 mg of purified recombinant G alpha have been obtained from 300-ml cultures of infected cells. The recombinant alpha subunits are myristoylated and are ADP-ribosylated by pertussis toxin only in the presence of beta gamma subunits. They bind guanosine 5'-3-O-(thio)triphosphate (GTP gamma S) with low nM dissociation constants and stoichiometries of 0.8 mol/mol or greater. The rGi1 alpha, rGi2 alpha, and rGi3 alpha are capable of interacting with angiotensin II receptors based on their ability to restore high affinity angiotensin II binding in rat liver membranes shifted to a low affinity state with GTP gamma S.
 ...
PMID:Expression and purification of functional G protein alpha subunits using a baculovirus expression system. 173 Jun 49

Systemic infusion of angiotensin II, a potent agonist, using doses that are initially subpressor, eventually produces sustained blood pressure elevation and reductions in glomerular capillary ultrafiltration coefficient characterized by enhanced signal transduction to angiotensin II and other agonists. In this setting, there is a significant increased affinity of angiotensin II binding to smooth muscle and glomerular mesangial receptors and enhanced sensitivity and magnitude of angiotensin II-induced decrements in cyclic AMP. Since G proteins are important modulators of binding and signal transduction, the present studies were designed to test the hypothesis that differences in the relative amounts of G proteins may be present and have accounted for differences observed. G proteins were identified and quantitated by isoelectric focusing/sodium dodecyl sulfate-polyacrylamide gel electrophoresis, radiolabeling in the presence of activated toxins with [gamma-32P]NAD+, immunoprecipitation, and immunoblotting. A 168% and 465% increase in pertussis toxin-catalyzed ADP ribosylation of alpha 40-41 was found in angiotensin II-treated groups over control groups for glomerular and mesenteric membranes, respectively. Immunoblotting revealed a 250% and 35% increase in the levels of the Gi isoforms alpha i-2 and alpha i-3, respectively, and a decrease of 53% in alpha i-1 from the angiotensin II-treated group. No differences were observed in cholera toxin labeling or immunoblotting of Gs. These results demonstrate multiple mechanisms whereby angiotensin-induced signal transduction can be modulated involving both the receptors and G proteins. These observed differences in G proteins in systemic and renal vasculature accompanying angiotensin II infusion suggest the possibility of a regulatory role in the pathophysiology of angiotensin II-induced hypertension and renal disease.
 ...
PMID:Angiotensin II-induced changes in guanine nucleotide binding and regulatory proteins. 173 48

The effects of angiotensin II on cytosolic free Ca2+ ion concentrations ([Ca2+]i) were studied in single porcine granulosa cells using the calcium-sensitive fluorescent dye fura-2 and high temporal resolution fluorescent videomicroscopy. Angiotensin II initiated specific, rapid, transient and topographically organized increases in [Ca2+]i in a subpopulation of single swine granulosa cells. The Ca2+ source for this angiotensin II-mediated [Ca2+]i transient appeared to be internal stores, and a pertussis toxin-sensitive guanine nucleotide binding protein was implicated in this receptor-mediated Ca2+ rise. Our single-cell studies also revealed a striking functional heterogeneity among granulosa cells, since follicle-stimulating hormone-responsive cells were not angiotensin II responsive. We conclude that single swine granulosa cells are targets of specific angiotensin II action on intracellular pools of Ca2+.
 ...
PMID:Angiotensin II induces calcium release in a subpopulation of single ovarian (granulosa) cells. 179 80

Cyclic GMP mediates vascular smooth muscle relaxation to a variety of drugs and naturally-occurring substances. The reduction of intracellular Ca2+ levels is believed to underlie this action, but the mechanism of this effect is unknown. In order to test the hypothesis that inhibition of guanine nucleotide-binding protein function is involved in the actions of cGMP, the effects of cGMP-dependent protein kinase on the phosphorylation of both pertussis toxin-sensitive (Gi/Go) and insensitive (Gz) G-proteins were examined in vitro. None of these proteins were effective substrates for either cGMP- or cAMP-dependent protein kinases, despite the fact that assay conditions were designed to detect poorly phosphorylated substrate proteins. In line with these observations, atriopeptin II did not inhibit angiotensin II-treated inositol phosphate formation in cultured vascular smooth muscle cells. These results suggest that phosphorylation by cGMP-dependent protein kinase of these G-proteins is not the major mechanism by which cGMP reduces intracellular Ca2+ levels in vascular smooth muscle.
 ...
PMID:Pertussis toxin-sensitive and insensitive guanine nucleotide binding proteins (G-proteins) are not phosphorylated by cyclic GMP-dependent protein kinase. 183 99

In a previous study, we have shown that freshly isolated glomerulosa cells possess dopamine (DA) receptors from both DA-1 and DA-2 subclasses, whereas in cultured conditions, cells exhibit dopamine receptors from the DA-1 subclass only. In the present work, we have studied the effect of DA on angiotensin-stimulated glomerulosa cells in these two experimental conditions. Our results demonstrate that in isolated cells, angiotensin II (AT) stimulates inositol phosphate accumulation, calcium influx and steroid secretion. Treatment with pertussis toxin completely blocks AT-stimulated steroid secretion and calcium influx and partially reduces inositol phosphate accumulation. DA alone has no effect on cAMP accumulation. However, in the presence of a specific DA-1 antagonist (SCH 23390), DA reduces intracellular cAMP content. Similarly, DA-like pertussis toxin produces the same inhibitory effects on AT-stimulated cells. The combined influence of DA and pertussis toxin is not additive suggesting that a 'Gi' GTP-binding protein is involved in the DA action. Specific DA antagonists indicate that these inhibitory processes are mediated through the DA-2 receptor subtype. DA may act by decreasing the intracellular calcium concentration since it reduces AT-stimulated Ca2+ influx and that both phospholipase C (PLC) and steroid accumulation are calcium dependent. Yet a direct inhibitory coupling between the DA-2 receptor and PLC may represent a second alternative since DA inhibitory effects are always present when calcium influx is artificially increased or decreased. In cultured cells, we observe an additive effect of DA and AT on aldosterone secretion, which is the result of additive interactions of the second messengers involved, namely cAMP for dopamine and inositol phosphates for angiotensin II. From these studies, we conclude that DA may exert a more versatile effect on aldosterone secretion than previously suspected.
 ...
PMID:Mechanisms involved in the interaction of dopamine with angiotensin II on aldosterone secretion in isolated and cultured rat adrenal glomerulosa cells. 183 52

As a target site for angiotensin II (A-II), renal proximal tubule is unique in that it may be equipped with a local A-II generating system and that both basolateral and apical membranes may be accessible for the action of A-II. We have recently conducted studies to examine these possibilities. With in vitro cultured proximal tubular cells, we have demonstrated de novo synthesis of angiotensinogen and renin. With isolated renal brush border membrane (BBM), we have confirmed the presence of A-II receptors and found that A-II directly stimulated BBM Na+/H+ exchange. In search of the signal transduction mechanism, we have found that A-II also activated BBM phospholipase A2 (PLA) and that BBM contained a pertussis toxin-sensitive guanine nucleotide binding protein (G-protein) which mediates the effects of A-II. Further studies showed that prevention of PLA activation abolished the effect of A-II on Na+/H+ exchange, and that activation of PLA by mellitin and the addition of arachidonic acid similarly enhanced BBM Na+/H+ exchange activity, suggesting that PLA activation may mediate the stimulatory effect of A-II on BBM Na+/H+ exchange. These results thus indicate that a local signal transduction mechanism involving G-protein mediated PLA activation exists in renal BBM which mediates the effect of A-II on Na+/H+ exchange. Taken together, we propose that, independent of A-II in the circulation, local luminal A-II may serve as an important regulatory system on sodium transport in renal proximal tubule.
 ...
PMID:Potential role for local luminal angiotensin II in proximal tubule sodium transport. 188 Oct 47

Angiotensin II can inhibit hormone-stimulated adenylyl cyclase in intact hepatocytes or in hepatic membrane preparations. Because the response can be blocked by pertussis toxin, the object of the present study was to determine which of the known variants of Gi can couple angiotensin II receptors to inhibition of adenylyl cyclase. The potential candidates were identified by probing RNA isolated from rat hepatocytes with cDNAs specific for the alpha subunits of known toxin-sensitive guanine nucleotide-binding regulatory proteins (G proteins). Hepatocytes contained no detectable RNA for the Go or Gi1 alpha subunits and similar levels of RNA coding for the Gi2 and Gi3 alpha subunits. To determine whether Gi3 could couple angiotensin receptors to inhibition of cyclase, membranes were prepared from hepatocytes whose G proteins were fully ADP-ribosylated with pertussis toxin, and the Gi3 holoprotein purified from rabbit liver was reconstituted into the membranes. The nature of the Gi3 reconstituted into the membrane was assessed by immunoblotting with antibodies specific for the Gi alpha subunits. Reconstitution of 6-10 pmol of Gi3/mg of membrane protein into the toxin-treated membranes restored the ability of 10 nM angiotensin II to inhibit adenylyl cyclase. Because pertussis toxin has nonspecific effects, an assay was developed to measure the interaction of the angiotensin receptor with reconstituted G proteins in normal membranes. In the presence of Mg2+, guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) caused a reduction of the affinity of the angiotensin II receptor for 125I-angiotensin II that was stable to washing and the detergents used to reconstitute G proteins into the membranes. Using this protocol to activate G proteins and "uncouple" receptors, the ability of the GDP-liganded form of Gi to restore high affinity binding was examined. Reconstitution of about 10-15 pmol of oligomeric Gi3/mg of membrane protein restored both the high affinity state of the angiotensin II receptor and the ability of GTP gamma S to shift the affinity to a lower state. The same shift in receptor affinity could be accomplished by reconstituting the Gi3 alpha subunit, resolved free of beta gamma subunits, into the membranes. Reconstitution of up to 50 pmol of Gs/mg of membrane protein had no effect on angiotensin II receptor affinity. The results suggest that a major form of Gi in hepatocytes is Gi3 and that it can couple angiotensin receptors to inhibition of adenylyl cyclase.
 ...
PMID:Inhibitory GTP-binding regulatory protein Gi3 can couple angiotensin II receptors to inhibition of adenylyl cyclase in hepatocytes. 190 48

When cultured in the presence of fetal calf serum, arterial smooth muscle cells from spontaneously hypertensive rats (SHR) proliferate more rapidly and are more numerous at confluency than cells from normotensive Wistar-Kyoto (WKY) animals. The phenomenon has been demonstrated in several laboratories but its molecular origin remains unclear. On the other hand phospholipase C activation and c-fos transcription are early events able to trigger cell mitosis. Therefore, the enhancement of inositol phosphates formation induced in SHR cells by various vasoactive agents and growth factors suggests that this enzyme might be implicated in the abnormal proliferation triggered by serum. In this case a unique molecular abnormality would be responsible for both arterial hypercontractility and dystrophy encountered in hypertension. In order to test this hypothesis we have compared DNA replication, phospholipase C activation, and c-jun and c-fos nuclear protooncogene transcriptions stimulated by fetal calf serum (FCS), vasoactive agents (angiotensin II and vasopressin), and epithelial growth factor (EGF) in SHR and WKY rat cells. The results obtained with these various agonists tested under the same experimental conditions confirm that the classical pathogenic diagram: (PLC hyperactivation----increase in c-fos transcription----enhanced cell proliferation) may apply to the action of vasoactive agents which are only slightly mitogenic on SHR cells, but not to the very important effect of fetal calf serum. Indeed, FCS stimulated inositol phosphate formation and c-jun and c-fos transcription, but none of these parameters was enhanced in SHR cells. Phospholipase C activation may exert some control upon DNA replication, as its partial inhibition by pertussis toxin coincided with an equivalent decrease in thymidine incorporation. It is, however, not absolutely required for the onset of DNA replication in aortic smooth muscle cells, as shown by the results obtained with EGF under the same experimental conditions. An abnormal molecular reaction different from PLC activation is therefore responsible for the enhanced proliferation of cultured SHR aortic smooth muscle cells, and several cell alterations may concur to the formation of the hypertensive arteriopathy.
 ...
PMID:Hyperactivation of phospholipase C does not support the enhanced proliferation of aortic smooth muscle cells from spontaneously hypertensive rats. 193 Aug 47

The carboxy terminal homologue of angiotensin II (Ang II), Ang-(3-8) or hexapeptide, was used as a model peptide to examine the types of receptor mechanisms involved in calcium mobilization in cultured vascular smooth muscle cells. Hexapeptide did not produce tachyphylaxis but did produce a sustained increase in intracellular calcium. Differences in the increase in intracellular calcium [( Ca2+]i) and the pattern of inositol phosphate production indicate that Ang-(3-8) and maximal concentrations of Ang II mobilize calcium through different mechanisms. The calcium-mobilizing mechanisms that predominate appear to depend on the concentration of angiotensin. Concentrations of Ang II greater than 10(-8) M produce sharp calcium transients in which the [Ca2+]i returns close to baseline within 1 minute after stimulation, but concentrations of Ang II equal to or less than 3 x 10(-9) M result in a plateau increase in calcium. Pretreatment with Bordetella pertussis toxin does not abolish either the calcium transient induced by Ang II or the plateau phase induced by Ang-(3-8), indicating that the GTP-transducing protein that couples the receptor to phospholipase C or, possibly, a receptor-operated calcium channel is not Bordetella pertussis toxin sensitive.
 ...
PMID:Regulation of cytosolic calcium by angiotensins in vascular smooth muscle. 211 11


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>