Biomedical subjects

T J Resink

Publications and source records attributed to T J Resink.

At least 55 records · Page 3Linked to original sources

PubMed1991

Low- and high-density lipoproteins as hormonal regulators of platelet, vascular endothelial and smooth muscle cell interactions: relevance to hypertension.

The major risk factors for cardiovascular disease include hypertension, hyperlipidemia, hyperinsulinemia and smoking. They promote the development of atherosclerosis and thromboembolic complications, i.e. strokes and heart attacks. There are diverse interactions between these factors, the outstanding common denominator being alterations in serum lipoproteins, mainly elevated low-density lipoprotein (LDL)-cholesterol and reduced high-density lipoprotein (HDL)-cholesterol concentrations, which results in disturbed cholesterol homeostasis (transport and metabolism) and eventually in perturbations of cellular integrity/function. In addition to their roles as cholesterol-transporting molecules, LDL and HDL directly influence inter- and intracellular communication via stimulation of pivotal signal transduction processes. The 'hormonal' effects of LDL on platelets, endothelial cells and vascular smooth muscle cells are potentially harmful, whereas the effects of HDL may be protective in as much as HDL can antagonize LDL-mediated stimulation of cells. Therapy aimed at reducing serum LDL-cholesterol levels and increasing HDL-cholesterol levels will have multifactorial beneficial effects on cardiovascular disease.

Animals↗

PubMed1990

Inducible endothelin mRNA expression and peptide secretion in cultured human vascular smooth muscle cells.

This study demonstrates the induction of endothelin (ET) mRNA expression and synthesis of functional ET peptide in cultured human vascular smooth muscle cells (hVSMC). Compounds eliciting such responses in hVSMC include the vasoconstrictor hormones angiotensin II and arginine-vasopressin and the growth factors transforming growth factor beta, platelet derived growth factor AA and epidermal growth factor. Induction of ET mRNA expression in hVSMC exhibited transient kinetics (peak at 3-5 hrs. and return to basal within 7 hrs.) which differed from the more sustained ET transcript induction observed for porcine endothelial cells. ET peptide (determined by both radioimmuno- and radioreceptor assays) produced by stimulated hVSMC attained levels (approximately 120-160 pg/10(6) cells/4 hrs.; concentration approximately 3 x 10(-11) M) within the biologically effective concentration range of ET. Stimulated secretion of ET from hVSMC was abolished in the presence of the protein synthesis inhibitor cycloheximide. Sep-pak C18 extracts of medium from stimulated hVSMC elicited a concentration-dependent phosphoinositide catabolic response in myo-[2-3H]-inositol-prelabelled hVSMC. Our findings invoke a role for ET which extends beyond the paracrine regulation by peptide synthesized and secreted by endothelial cells. We propose that VSMC-synthesized ET may function in an autocrine manner to regulate both tone and structural modelling of vasculature.

Angiotensin II↗

PubMed1990

Activation of multiple signal transduction pathways by endothelin in cultured human vascular smooth muscle cells.

Cellular responses to the vasoconstrictor peptide, endothelin, have been investigated in quiescent cultured human vascular smooth muscle cells (hVSMC). Endothelin caused intracellular alkalinization and activation of the protein synthetic enzyme S6-kinase, but such responses were not associated with any mitogenic effects of endothelin on hVSMC. In myo-[3H]inositol-prelabelled hVSMC endothelin elicited a rapid increase in inositol bis- and tris-phosphates and concomitant hydrolysis of polyphosphoinositol lipids. In [3H]arachidonate-prelabelled hVSMC endothelin promoted production of diacylglycerol, the early kinetics of which parallelled polyphosphoinositol lipid hydrolysis. Such phospholipase C activation by endothelin was sustained in hVSMC with accumulation of inositol polyphosphates being markedly protracted and the decay of diacylglycerol slow. Endothelin promoted extracellular release of [3H]arachidonate-labelled material from hVSMC which derived via deacylation of both phosphatidylinositol and phosphatidylcholine. This process was inhibited by phospholipase A2 and lipoxygenase inhibitors, but insensitive to phospholipase C and cyclooxygenase inhibitors. Endothelin-induced activation of phospholipase C and phospholipase A2 signal transduction pathways (EC50 approximately 5-8 nM for both) in hVSMC apparently proceed in an independent parallel manner rather than a sequential one.

Arachidonic Acid↗

PubMed1990

Phorbol ester promotes a sustained down-regulation of endothelin receptors and cellular responses to endothelin in human vascular smooth muscle cells.

The effect of phorbol ester pretreatment of human vascular smooth muscle cells (hVSMC) was studied with respect to regulation of endothelin (ET)-receptor binding and cellular responses to ET. The capacity of hVSMC to bind ET was decreased (by approximately 50% at maximum) after phorbol exposure, and this reductive effect was both rapid (t 1/2 approximately 10 min.) and sustained (for up to 24 hrs. of chronic phorbol exposure). Phorbol pretreatment inhibited both inositol phosphate and diacylclycerol production responses of hVSMC to ET in a manner that was time-dependent and sustained. Phorbol pretreatment also produced a persistent reduction in the ability of ET to release isotopically-labelled arachidonic and/or its metabolites from hVSMC, but importantly ionomycin-stimulated release was similarly negatively affected. Furthermore, ET-induced accumulation of the phospholipase A2/phospholipase B-derived inositol phospholipid metabolite, glycerophosphoinositol, was not different between control and phorbol-treated hVMSC. The mechanism whereby phorbol exerts differential, but notably sustained inhibitory effects on ET-promoted signal transduction pathways are thus complex and illustrative of the selectivity of protein kinase C in regulating cellular responses.

Arachidonic Acid↗

PubMed1990

Specific growth stimulation of cultured smooth muscle cells from spontaneously hypertensive rats by platelet-derived growth factor A-chain homodimer.

Cultured vascular smooth muscle cells (VSMC)1 from spontaneously hypertensive rats (SHR) possess specific cell surface receptors for both homodimeric forms of platelet-derived growth factor (PDGF-AA and PDGF-BB), in contrast to cells from normotensive Wistar Kyoto (WKY) animals, which express receptors only for the B-chain form of PDGF. Stimulation of quiescent VSMC from SHR with PDGF-AA resulted in activation of S6-kinase and induction of phosphoinositide catabolism, as well as cellular proliferation when cultures were maintained for prolonged periods with daily supplementation of the growth factor. WKY-derived VSMC showed no response to PDGF-AA, which was consistent with their lack of specific receptors for this homodimer. The responsiveness of quiescent cells from SHR and WKY to the B-chain homodimer was similar. The enhanced growth responsiveness of SHR-derived cells to fetal calf serum, as compared with cells from their normotensive counterparts, may be accounted for in part by their expression of receptors for the AA homodimer of PDGF.

Animals↗

PubMed1990

Stimulation of endothelin mRNA and secretion in rat vascular smooth muscle cells: a novel autocrine function.

Endothelin (ET), a peptide originally isolated from the supernatants of cultured endothelial cells, exerts a wide variety of biological effects in different tissues. Endothelial-cell-synthesized ET-1 has been proposed to act in a paracrine manner on adjacent smooth muscle cells (SMC) in vivo, with effects that include both vascular reactivity (vasodilation/vasoconstriction) and mitogenesis. This study, by the use of immunocytochemically characterized SMC (rVSMC) isolated from the aortas of spontaneously hypertensive rats, has investigated a possible autocrine role for ET in regulation of the vasculature. Although quiescent cultures of rVSMC apparently did not constitutively express prepro ET-1mRNA, ET-specific transcripts could be induced by a variety of growth factors (transforming growth factor beta [TGF-beta]; platelet-derived growth factor-AA homodimer [PDGF-A chain]) and vasoactive hormones (angiotensin II [Ang II], arginine-vasopressin, and ET-1 itself). The kinetics for prepro ET-1mRNA induction in rVSMC were characteristically rapid in onset and transient. Down-regulation of protein kinase C by 48 h pretreatment of rVSMC with phorbol ester markedly reduced the subsequent ability of rVSMC to express ET-1 transcripts and secrete ET-1 peptide in response to Ang II. Inducible prepro ET-1mRNA expression was accompanied by a cycloheximide-inhibitable release of ET-1 peptide into the medium of rVSMC. ET-1 peptide was determined by both radioreceptor- and radioimmunoassay. Stimulated rVSMC accumulated ET-1 (approximately 200 pg.10(6) cells-1 x 4 h-1) at levels that attained biological relevance (approximately 10(-10) M). Sep-pak C18 extracts of medium from stimulated rVSMC elicited contraction of isolated endothelium-denuded rat mesenteric resistance vessels, and this response was characteristically protracted and difficult to "wash out." Synthetic (porcine) ET-1 promoted the expression of transcripts for PDGF-A chain, TGF-beta, and thrombospondin in quiescent rVSMC. Such effects of ET-1 on gene expression may be relevant to the mitogenic potential of ET-1 on VSMC. Our findings imply a role for ET-1 in the control of vascular function via both paracrine and autocrine regulatory mechanisms. The expression of prepro ET-1mRNA and peptide biosynthesis by rVSMC may have both short-term (e.g., vasoconstriction) and long-term (e.g., structural remodeling) consequences. A sustained loop of autocrine stimulation by ET-1 in SMC could contribute toward the pathogenesis of vasospasm and/or atherosclerosis.

Animals↗

PubMed1990

Endothelin messenger RNA and receptors are differentially expressed in cultured human breast epithelial and stromal cells.

Paracrine regulation is implicit in the biosynthesis and secretion of milk in the breast. An important determinant for this regulation in vivo is proximate cellular location as exemplified by stromal and epithelial cells in breast tissue. Cultured human breast epithelial cells exhibited low constitutive expression of mRNA for endothelin which was enhanced 20-fold after prolactin stimulation. Human breast stromal cells did not express measurable levels of endothelin mRNA under similar conditions. In a similar differential manner, the stimulated release of immunoreactive endothelin into medium overlay was observed only for breast epithelial and not stromal cells. Specific cell-surface receptors for endothelin and biochemical responsiveness to the peptide were observed only in the stromal cells.

Breast↗

PubMed1990

Modulation of extracellular matrix by angiotensin II: stimulated glycoconjugate synthesis and growth in vascular smooth muscle cells.

A role for angiotensin II (Ang II) in the pathogenesis of hypertension and atherosclerosis was studied using cultured vascular smooth muscle cells from spontaneously hypertensive rats. Chronic exposure of vascular smooth muscle cells, cultured in the presence of 1% plasma-derived serum, to Ang II resulted in a dose-dependent stimulation in growth and incorporation of radiolabeled matrix precursors into extracellular matrix-associated glycoconjugate material. The hormone also stimulated the incorporation of [3H]glycine into extracellular matrix glycoproteins and proteoglycans synthesized by cultures rendered quiescent by maintenance on serum-free medium for 48 h prior to exposure to Ang II. This was negated in the presence of saralasin. In quiescent cultures, a single exposure to angiotensin induced a rapid induction of mRNA coding for the extracellular matrix glycoprotein thrombospondin. Similar results were obtained with cells maintained on medium containing 1% plasma-derived serum; however, the levels of induction were reduced by this procedure. This study demonstrated that Ang II was capable of stimulating both growth and matrix elaboration by cultured vascular smooth muscle cells. These observations are indicative of a pathophysiological role for the vasoconstrictor peptide, which may contribute significantly to the development of hypertension.

Angiotensin II↗

PubMed1990

Induction of thrombospondin expression in vascular smooth muscle cells by angiotensin II.

Vascular smooth muscle cells (VSMCs), unlike cardiac or skeletal myocytes, are capable of undergoing reversible phenotypic modulation from "contractile" to "proliferative/synthetic" cells in vivo. We have investigated the ability of angiotensin II (Ang II) to influence this process via modulation of extracellular matrix synthesis. Ang II induced a rapid (within 2 h), dose (10(-6)-10(-9) M)-dependent stimulation (14-fold) of thrombospondin (TSP) gene expression in rat VSMCs in the absence of additional factors. This was followed by an enhanced platelet-derived growth factor (PDGF) A chain and transforming growth factor-beta (TGF beta) gene expression. These effects of Ang II could be negated by the simultaneous addition of saralasin (IC50 approximately 10(-9) M for Ang II at 10(-7) M) to cells. Transcription levels for TSP were further enhanced (to 28 X control values) by 6 h, at which time the synthesis of PDGF A chain mRNA was maximal. Although exposure of cells to TSP (5 X 10(-8) M) stimulated signal transduction pathways, it did not enhance levels of either PDGFA or TGF beta transcripts. The glycoconjugate content of extracellular matrices elaborated by cells chronically exposed to Ang II was elevated compared to control cultures and there was a small increase in cell number.

Angiotensin II↗

PubMed1990

Internalization of endothelin by cultured human vascular smooth muscle cells: characterization and physiological significance.

The binding and internalization of 125I-endothelin (125I-ET-1) was studied in cultured human vascular smooth muscle cells (hVSMC). Discrimination between surface-bound and internalized radiolabeled ligand was achieved using either acetic acid or trypsin treatment of cell layers, with the two procedures yielding comparable results. Total cellular 125I-ET-1 binding hVSMC at 37 degrees was rapid and reached near equilibrium within 30 min. Such binding could be resolved into surface-bound (acid/trypsin-sensitive) and internalized (acid/trypsin-resistant) components. The accumulation of internalized 125I-ET-1 was temperature dependent and occurred at 37 degrees (t1/2 approximately 15 min) but not at 4 degrees. Internalization of 125I-ET-1 by hVSMC was reversibly inhibited by the transglutaminase inhibitor dansylcadaverine (half-maximal inhibitory concentration, approximately 400 microM). Cytosolic acidification of hVSMC (from pH approximately 6.8 to approximately 6.3) by incubation with potassium acetate in a choline buffer also inhibited 125I-ET-1 internalization. Our observation indicate that smooth muscle cells internalize ET-1 via the clathrin-mediated endocytotic pathway. Dansylcadaverine and other inhibitors of transglutaminase inhibited ET-1-stimulated inositol phospholipid hydrolysis in hVSMC and decreased ET-1-induced vasoconstriction in isolated endothelium-denuded blood vessels. Internalization of ET-1 may, therefore, be relevant to the characteristically protracted physiological effects of this peptide on the vasculature.

Cadaverine↗

PubMed1989

Induction of growth-related metabolism in human vascular smooth muscle cells by low density lipoprotein.

Human vascular smooth muscle cells (hVSMC) rendered quiescent by maintenance under serum-free culture conditions for 48 h exhibited several metabolic responses, normally associated with proliferation, following exposure to low density lipoprotein (LDL). LDL induced a time- and dose- (half-maximally effective concentration, ED50 25.0 +/- 8 nM) dependent activation of S6 kinase which could be negated following pretreatment of hVSMC with 12-O-tetradecanoylphorbol-13-acetate (TPA) for 48 h. In myo-[3H]inositol-prelabeled hVSMC, LDL caused a rapid (maximum within 1 min) decrease in phosphatidylinositol 4,5-bisphosphate (35% p less than 0.001) and phosphatidylinositol 4-phosphate (20%, p less than 0.01) with a return to prestimulated levels within 5-10 min. LDL induced a concomitant increase in [3H]inositol phosphates for which the order of generation was inositol-tris greater than -bis greater than -mono phosphate and which reached threshold levels of significance (p less than 0.05) above control values within 1, 2, and 10 min, respectively. The effect of LDL on hVSMC phosphoinositide metabolism was dose-dependent (half-maximally effective concentration, ED50 32.1 +/- 5.0 nM). This concentration, like that for S6 kinase, approximates with the KD (5-21 nM) for high affinity binding of 125I-LDL to specific receptors (1.5 x 10(4) sites/cell) on hVSMC. LDL induced a rapid but transient translocation of protein kinase C from the cytosol to membranes as assessed using both immunoblotting and [3H] 4-beta-phorbol-12-13-dibutyrate-binding procedures. Exposure of quiescent hVSMC to LDL elevated intracellular pH (delta pH 0.30 +/- 0.03, p less than 0.001). Such alkalinization was prevented in the presence of Na+/K+ exchange inhibitors such as amiloride, dimethylamiloride, and ethylisopropylamiloride. In an investigation of the nuclear action of LDL, a time-dependent induction of both c-myc and c-fos was observed. Such LDL-induced expression of these nuclear proto-onco-genes was not detectable in protein kinase C down-regulated hVSMC. Nevertheless, in spite of the cascade of "growth-promotional" responses elicited by LDL in quiescent hVSMC, this lipoprotein alone (under serum-free conditions) was neither mitogenic in nuclear labeling experiments, nor could it support growth of hVSMC in culture. We demonstrate that LDL might function in a complementary/synergistic fashion with other weakly mitogenic (to VSMC) growth factors and suggest that activation of protein kinase C (vis à vis intrinsic tyrosine kinase characteristic of other growth factor receptors) may be crucial to the signal transduction pathway for LDL.

Arterioles↗

PubMed1989

Differential stimulation of growth related metabolism in cultured smooth muscle cells from SHR and WKY rats by combinations of EGF and LDL.

We have reported previously that vascular smooth muscle cells from spontaneously hypertensive rats (SHR) were more responsive to epidermal growth factor (EGF) than their normotensive derived Wistar Kyoto (WKY) controls. This differential responsiveness is evident for several cellular processes including activation of S6-kinase, elevation of intracellular pH and stimulation of both phosphoinositide metabolism and DNA synthesis. Quiescent smooth muscle cells exposed to low density lipoprotein (LDL) exhibited a similar differential responsiveness (SHR greater than WKY) in terms of S6-kinase activation, which was time- and dose-dependent (10(-10)-10(7) M), but neither cell type responded appreciably to LDL in terms of a stimulation in [3H]-thymidine incorporation. Exposure of the same cells to EGF and LDL in combination elicited a marked synergistic stimulation in DNA synthesis, the extent of which was greater for SHR than WKY. The sensitivity of both cell types to EGF was increased in the presence of LDL, although cells from hypertensive animals still exhibited their greater (vs. WKY) sensitivity. In both cell types, activation of nuclear protooncogenes c-fos and c-myc by LDL was minimal, whereas oncogene induction by EGF was approximately five-fold greater for SHR-derived cells compared to those from WKY animals. No marked synergistic effect on the time-dependent induction of either entity was observed for cells exposed to EGF and LDL simultaneously, and the response of SHR-cells remained greater than WKY-cells.

Animals↗

PubMed1989

Activation of phospholipase A2 by endothelin in cultured vascular smooth muscle cells.

The ability of endothelin to promote phospholipid hydrolysis has been studied in myo-[2-3H]-inositol-, [3H]-arachidonic acid- or methyl-[3H]choline chloride-prelabelled cultured vascular smooth muscle cells (VSMC) from rat and bovine thoracic aortae and human omental vessels. The biochemical responses to endothelin were comparable between the different VSMC isolates. Endothelin promoted the accumulation of glycerolphospho[3H]inositol and concomitant loss of [3H]-inositol label from phosphatidylinositol. Exposure of [3H]choline-labelled VSMC to endothelin resulted in a loss of radioactivity from phosphatidylcholine that was inversely parallelled by an increase in water-soluble [3H]-choline metabolites. In [3H]-arachidonic acid ([3H]-AA)-labelled VSMC, endothelin induced extracellular release of [3H]-AA which derived from both phosphatidylcholine and phosphatidylinositol. Half-maximally effective concentrations of endothelin for all these responses were approximately 2-7 nM and did not vary between VSMC types. Endothelin-induced release of [3H]-AA into VSMC medium-overlay was inhibited by quinacrine and nordihydroguaiaretic acid but not by neomycin or indomethacin. The data herein implicate activation of phospholipase A2 by endothelin with subsequent metabolism of arachidonic acid via the lipoxygenase pathway.

Animals↗

PubMed1989

Decreased susceptibility of cultured smooth muscle cells from SHR rats to growth inhibition by heparin.

Smooth muscle cell proliferation is regulated through the coordinated action of growth inhibitors and growth factors/mitogens; a specific heparin-epidermal growth factor (EGF) complementation has been proposed (Reilly et al., 1987, J. Cell. Physiol., 131:149-157). In culture, vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) proliferate more rapidly than VSMC from control Wistar Kyoto rats (WKY). We observed that, compared with WKY-derived VSMC, cells from SHR were markedly less susceptible to growth inhibition both by heparin and its homopolysaccharide analogue pentosan polysulphate (PPS). SHR-derived VSMC exhibited a reduced capacity for binding of [3H]heparin to specific extracellular surface receptors, whereas affinities for heparin were comparable between both VSMC isolates. The early (0-2 hr at 37 degrees C) kinetics of internalization did not differ between SHR- and WKY-derived VSMC, but both internalized equivalent proportions (approximately 10%) of initially surface-bound heparin. VSMC from SHR exhibited a greater capacity, without a changed affinity, for [I125]EGF binding than VSMC from WKY. Pre-exposure of VSMC to heparin or PPS decreased, in a time-dependent manner, the EGF binding capacity for both SHR and WKY (by 40-50% after 72 hr). However, in absolute terms, the EGF-binding capacity of VSMC from SHR exposed to heparinoids was similar to that of nonexposed VSMC from WKY.

Animals↗

PubMed1989

Extracellular matrix: differential influence on growth and biosynthesis patterns of vascular smooth muscle cells from SHR and WKY rats.

Smooth muscle cells from spontaneously hypertensive rats (SHR) elaborated extracellular matrix (ECM) material in culture that was more stimulatory to growth of cells from normotensive (WKY) animals than their own matrix. Both cell types elaborated ECMs consisting of glycoconjugate material (proteoglycans, glycopeptides) elastin, and collagens, but there were differences in the relative proportions of the compounds synthesized. Cells from SHR produced an ECM richer in elastin than that synthesized by WKY derived cells (approximately 19% vs. 11%, respectively). However, the latter elaborated ECMs containing more (approximately 45% for WKY vs. 29% for SHR) glycoconjugate material than the former. The lysyloxidase-mediated cross-linking of elastin was more rapid in cultured cells from SHR animals than from their normotensive counterparts and may be as a consequence of increased substate (tropoelastin) availability in ECMs from SHR animals. The relative proportions and sulphate levels of the glycosaminoglycans associated with matrix material elaborated by the two cell types were similar. Radiolabelled glycoconjugate material was degraded by cells (SHR/WKY) when they were plated upon pre-formed ECMs, and their patterns of synthesis of new matrix was markedly altered under such conditions. New matrix material elaborated by cells plated upon ECM-coated dishes consisted predominantly of glycopeptide and proteoglycan matrix components. Epidermal growth factor promoted the incorporation of [3H]-thymidine into DNA by quiescent cells, and this was also markedly stimulated when cells were plated onto ECM-coated plasticware rather than onto plastic substratum.

Animals↗

PubMed1989

Regulation of phosphoinositide turnover in endothelium from human pulmonary artery, aorta and umbilical vein. Antagonistic action on the beta-adrenoceptor coupled adenylate cyclase system.

Ca2+-mobilizing receptor-induced inositol phospholipid hydrolysis has been studied in cultured endothelial cells (EC) from human aorta, pulmonary artery, and umbilical vein. It was shown that in EC the release of inositol phosphates can be stimulated by histamine, thrombin, serotonin, acetylcholine, carbachol, bradykinin, vasopressin, angiotensin II, platelet-activating factor (PAF), the thromboxane A2 mimetic, U46619, and prostaglandin E2. The most effective agonists were thrombin, histamine, and PAF, producing two- to five-fold increases in inositol phosphate level, and a 50-90% elevation of the level of inositol trisphosphate within 5 min. Effects of other agonists were smaller, although significant. Incubation of EC with histamine or PAF for 1 h resulted in a four- to eight-fold decrease of beta-adrenoreceptor density in the plasma membranes. The activity of isoproterenol-stimulated adenylate cyclase was depressed, and the degree of stimulation by isoproterenol was reduced. Similar effects were obtained after treatment of EC with the protein kinase C activator 4 beta-phorbol 12 beta-myristate 13 alpha-acetate, suggesting a role of protein kinase C in receptor desensitization. It is concluded, that stimulation of inositol phospholipid hydrolysis, and, consequently, activation of protein kinase can cause receptor imbalance in human vascular endothelium. This mechanism may play a pivotal role in the pathogenesis of cardiovascular and pulmonary diseases.

Adenylyl Cyclases↗

PubMed1989

Synergistic potentiation of polyphosphoinositide breakdown by adenylate cyclase coupled receptors in human endothelial cells.

Histamine induces dose-dependent increases in inositol-monophosphate, inositol-bisphosphate, and inositol-triphosphate in cultured human pulmonary artery and umbilical vein endothelial cells. Preincubation with isoproterenol results in synergistic potentiation of polyphosphoinositide breakdown. Isoproterenol does not change the effect of histamine, however, it does increase the potency of histamine in stimulating phosphoinositide turnover. This effect of isoproterenol is time-dependent reaching 350% at 120 min of preincubation. A synergistic potentiation of histamine-induced polyphosphoinositide breakdown by cyclic AMP stimulators has been observed after pretreatment of cultured endothelial cells with forskolin, dibutyryl cyclic AMP and cholera toxin. Our data suggest that isoproterenol potentiates histamine-induced polyphosphoinositide breakdown by operating via the adenylate cyclase system. This is the first evidence of synergistic potentiation of polyphosphoinositide breakdown by adenylate cyclase-coupled receptors in cultured human endothial cells.

Adenylyl Cyclases↗

PubMed1989

Atrial natriuretic peptide: binding and cyclic GMP response in cultured vascular smooth muscle cells from spontaneously hypertensive rats.

Atrial natriuretic peptide (ANP) is vasodilatory and natriuretic, but whereas increased plasma ANP levels occur in spontaneously hypertensive rats, their elevated vascular resistance suggests inappropriate target tissue responsiveness to ANP. This study examines ANP-receptor binding properties (at 25 degrees C and 4 degrees C) in cultured vascular aortic smooth muscle cells from spontaneously hypertensive (SHR) and control Wistar-Kyoto (WKY) rats. [I125]-human ANP saturation (0.0625-12.0 nmol) profiles were analyzed using nonlinear regression (LIGAND). Vascular smooth muscle cells from WKY possessed both high affinity (KD1 0.3 nmol; R1 33 fmol/10(5) cells) and low affinity (KD2 15 nmol; R2 400 fmol/10(5) cells) binding sites for ANP. In contrast, for smooth muscle cells from SHR, two receptor forms could not be resolved using identical analytical protocols. Parameter estimates at 25 degrees C and 4 degrees C were not different for either SHR or WKY. The number of receptors for SHR (Bmax approximately 100 fmol/10(5) cells) was lower than the total number of receptors for WKY (high plus low affinity approximately 430 fmol/10(5) cells). The intermediary KD value (approximately 1.0 nmol) for ANP binding in SHR suggests an ANP-receptor interconversion from high affinity to low affinity in smooth muscle cells from SHR. Competition-binding experiments also revealed a decreased affinity for ANP in SHR-derived smooth muscle cells. The cyclic GMP response (intracellular accumulation and extracellular levels) was decreased in SHR smooth muscle cells compared to WKY, although this difference was evident only after prolonged (one hour) stimulation with ANP. Our data indicate a reduced sustained vascular responsiveness to ANP in hypertension.

Animals↗