RESUMEN
The mechanisms by which NaCl raises blood pressure (BP) in hypertension are unresolved, but much evidence indicates that endogenous ouabain is involved. In rodents, arterial smooth muscle cell (ASMC) Na(+) pumps with an α(2)-catalytic subunit (ouabain EC(50) ≤1.0 nM) are crucial for some hypertension models, even though ≈80% of ASMC Na(+) pumps have an α(1)-subunit (ouabain EC(50) ≈ 5 µM). Human α(1)-Na(+) pumps, however, have high ouabain affinity (EC(50) ≈ 10-20 nM). We used immunoblotting, immunocytochemistry, and Ca(2+) imaging (fura-2) to examine the expression, distribution, and function of Na(+) pump α-subunit isoforms in human arteries and primary cultured human ASMCs (hASMCs). hASMCs express α(1)- and α(2)-Na(+) pumps. Further, α(2)-, but not α(1)-, pumps are confined to plasma membrane microdomains adjacent to sarcoplasmic reticulum (SR), where they colocalize with Na/Ca exchanger-1 (NCX1) and C-type transient receptor potential-6 (receptor-operated channels, ROCs). Prolonged inhibition (72 h) with 100 nM ouabain (blocks nearly all α(1)- and α(2)-pumps) was toxic to most cultured hASMCs. Treatment with 10 nM ouabain (72 h), however, increased NCX1 and sarco(endo)plasmic reticulum Ca(2+)-ATPase expression and augmented ATP (10 µM)-induced SR Ca(2+) release in 0 Ca(2+), ouabain-free media, and Ca(2+) influx after external Ca(2+) restoration. The latter was likely mediated primarily by ROCs and store-operated Ca(2+) channels. These hASMC protein expression and Ca(2+) signaling changes are comparable with previous observations on myocytes isolated from arteries of many rat hypertension models. We conclude that the same structurally and functionally coupled mechanisms (α(2)-Na(+) pumps, NCX1, ROCs, and the SR) regulate Ca(2+) homeostasis and signaling in hASMCs and rodent ASMCs. These ouabain/endogenous ouabain-modulated mechanisms underlie the whole body autoregulation associated with increased vascular resistance and elevation of BP in human, salt-sensitive hypertension.
Asunto(s)
Señalización del Calcio/efectos de los fármacos , Músculo Liso Vascular/efectos de los fármacos , Miocitos del Músculo Liso/efectos de los fármacos , Ouabaína/farmacología , Cloruro de Sodio/farmacología , Intercambiador de Sodio-Calcio/efectos de los fármacos , Resistencia Vascular/efectos de los fármacos , Adolescente , Adulto , Anciano , Animales , Presión Sanguínea/efectos de los fármacos , Western Blotting , Cardenólidos/metabolismo , Membrana Celular/efectos de los fármacos , Membrana Celular/metabolismo , Forma de la Célula/efectos de los fármacos , Supervivencia Celular/efectos de los fármacos , Células Cultivadas , Relación Dosis-Respuesta a Droga , Femenino , Homeostasis , Humanos , Hipertensión/inducido químicamente , Hipertensión/metabolismo , Hipertensión/fisiopatología , Inmunohistoquímica , Receptores de Inositol 1,4,5-Trifosfato/efectos de los fármacos , Receptores de Inositol 1,4,5-Trifosfato/metabolismo , Masculino , Arterias Mamarias/efectos de los fármacos , Arterias Mamarias/metabolismo , Ratones , Ratones Endogámicos C57BL , Microscopía Fluorescente , Persona de Mediana Edad , Músculo Liso Vascular/metabolismo , Músculo Liso Vascular/fisiopatología , Miocitos del Músculo Liso/metabolismo , Ratas , Saponinas/metabolismo , Retículo Sarcoplasmático/efectos de los fármacos , Retículo Sarcoplasmático/metabolismo , ATPasas Transportadoras de Calcio del Retículo Sarcoplásmico/metabolismo , Cloruro de Sodio/toxicidad , Intercambiador de Sodio-Calcio/metabolismo , ATPasa Intercambiadora de Sodio-Potasio/antagonistas & inhibidores , ATPasa Intercambiadora de Sodio-Potasio/metabolismo , Canales Catiónicos TRPC/efectos de los fármacos , Canales Catiónicos TRPC/metabolismo , Factores de Tiempo , Regulación hacia Arriba , Adulto JovenRESUMEN
Mice with smooth muscle (SM)-specific knockout of Na(+)/Ca(2+) exchanger type-1 (NCX1(SM-/-)) and the NCX inhibitor, SEA0400, were used to study the physiological role of NCX1 in mouse mesenteric arteries. NCX1 protein expression was greatly reduced in arteries from NCX1(SM-/-) mice generated with Cre recombinase. Mean blood pressure (BP) was 6-10 mmHg lower in NCX1(SM-/-) mice than in wild-type (WT) controls. Vasoconstriction was studied in isolated, pressurized mesenteric small arteries from WT and NCX1(SM-/-) mice and in heterozygotes with a global null mutation (NCX1(Fx/-)). Reduced NCX1 activity was manifested by a marked attenuation of responses to low extracellular Na(+) concentration, nanomolar ouabain, and SEA0400. Myogenic tone (MT, 70 mmHg) was reduced by approximately 15% in NCX1(SM-/-) arteries and, to a similar extent, by SEA0400 in WT arteries. MT was normal in arteries from NCX1(Fx/-) mice, which had normal BP. Vasoconstrictions to phenylephrine and elevated extracellular K(+) concentration were significantly reduced in NCX1(SM-/-) arteries. Because a high extracellular K(+) concentration-induced vasoconstriction involves the activation of L-type voltage-gated Ca(2+) channels (LVGCs), we measured LVGC-mediated currents and Ca(2+) sparklets in isolated mesenteric artery myocytes. Both the currents and the sparklets were significantly reduced in NCX1(SM-/-) (vs. WT or NCX1(Fx/-)) myocytes, but the voltage-dependent inactivation of LVGCs was not augmented. An acute application of SEA0400 in WT myocytes had no effect on LVGC current. The LVGC agonist, Bay K 8644, eliminated the differences in LVGC currents and Ca(2+) sparklets between NCX1(SM-/-) and control myocytes, suggesting that LVGC expression was normal in NCX1(SM-/-) myocytes. Bay K 8644 did not, however, eliminate the difference in myogenic constriction between WT and NCX1(SM-/-) arteries. We conclude that, under physiological conditions, NCX1-mediated Ca(2+) entry contributes significantly to the maintenance of MT. In NCX1(SM-/-) mouse artery myocytes, the reduced Ca(2+) entry via NCX1 may lower cytosolic Ca(2+) concentration and thereby reduce MT and BP. The reduced LVGC activity may be the consequence of a low cytosolic Ca(2+) concentration.
Asunto(s)
Presión Sanguínea/fisiología , Canales de Calcio Tipo L/fisiología , Músculo Liso Vascular/fisiología , Intercambiador de Sodio-Calcio/genética , Intercambiador de Sodio-Calcio/fisiología , Vasoconstricción/fisiología , Ácido 3-piridinacarboxílico, 1,4-dihidro-2,6-dimetil-5-nitro-4-(2-(trifluorometil)fenil)-, Éster Metílico/farmacología , Compuestos de Anilina/farmacología , Animales , Arterias/anatomía & histología , Arterias/fisiología , Western Blotting , Agonistas de los Canales de Calcio/farmacología , Señalización del Calcio/efectos de los fármacos , Electrofisiología , Proteínas Fluorescentes Verdes , Indicadores y Reactivos , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Tono Muscular/fisiología , Miocitos del Músculo Liso/fisiología , Técnicas de Placa-Clamp , Éteres Fenílicos/farmacología , Intercambiador de Sodio-Calcio/antagonistas & inhibidores , TelemetríaRESUMEN
Natriuretic peptides are a family of three structurally related hormone/ paracrine factors. Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) are secreted from the cardiac atria and ventricles, respectively. ANP signals in an endocrine and paracrine manner to decrease blood pressure and cardiac hypertrophy. BNP acts locally to reduce ventricular fibrosis. C-type natriuretic peptide (CNP) primarily stimulates long bone growth but likely serves unappreciated functions as well. ANP and BNP activate the transmembrane guanylyl cyclase, natriuretic peptide receptor-A (NPR-A). CNP activates a related cyclase, natriuretic peptide receptor-B (NPR-B). Both receptors catalyze the synthesis of cGMP, which mediates most known effects of natriuretic peptides. A third natriuretic peptide receptor, natriuretic peptide receptor-C (NPR-C), clears natriuretic peptides from the circulation through receptor-mediated internalization and degradation. However, a signaling function for the receptor has been suggested as well. Targeted disruptions of the genes encoding all natriuretic peptides and their receptors have been generated in mice, which display unique physiologies. A few mutations in these proteins have been reported in humans. Synthetic analogs of ANP (anaritide and carperitide) and BNP (nesiritide) have been investigated as potential therapies for the treatment of decompensated heart failure and other diseases. Anaritide and nesiritide are approved for use in acute decompensated heart failure, but recent studies have cast doubt on their safety and effectiveness. New clinical trials are examining the effect of nesiritide and novel peptides, like CD-NP, on these critical parameters. In this review, the history, structure, function, and clinical applications of natriuretic peptides and their receptors are discussed.
Asunto(s)
Natriuréticos/farmacología , Péptidos Natriuréticos/metabolismo , Receptores del Factor Natriurético Atrial/metabolismo , Secuencia de Aminoácidos , Animales , Factor Natriurético Atrial/farmacología , Historia del Siglo XX , Humanos , Péptido Natriurético Encefálico/farmacología , Péptidos Natriuréticos/historia , Péptidos Natriuréticos/farmacología , Fragmentos de Péptidos/farmacologíaRESUMEN
Natriuretic peptide receptors A (NPR-A) and B (NPR-B) mediate most effects of natriuretic peptides by synthesizing cGMP. ATP increases the activity of these receptors by an unknown mechanism. We recently reported that a nonhydrolyzable form of ATP, adenylyl imidodiphosphate (AMPPNP), stabilizes but is not required for the activation of NPR-A and NPR-B in membranes from highly overexpressing cells. Here, we repeated these studies on receptors expressed in endogenous settings. Kinetic analysis indicated that both AMPPNP and ATP dramatically decrease the apparent K(m) of both receptors for GTP but had little effect on the V(max). The EC(50) for AMPPNP decreased as substrate concentration increased whereas the magnitude of the effect was greater at lower GTP concentrations. ATP increased the activity of a mutant receptor containing glutamates substituted for all known phosphorylation sites similarly to the wild-type receptor, consistent with a phosphorylation independent mechanism. Finally, the putative ATP binding sites were investigated. Mutation of the ATP modulatory domain region had no effect, but mutation of K535A dramatically diminished ANP-dependent cyclase activity in a manner that was unresponsive to ATP. Mutation of the highly conserved 630-KSS to AAA (all alanines) resulted in an expressed receptor that had no detectable guanylyl cyclase activity. We conclude that ATP is not required for the initial activation of NPRs but does increase activity over time by reducing the apparent K(m) for GTP.
Asunto(s)
Nucleótidos de Adenina/farmacología , Guanosina Trifosfato/metabolismo , Receptores del Factor Natriurético Atrial/metabolismo , Adenosina Trifosfato/análogos & derivados , Adenosina Trifosfato/análisis , Adenosina Trifosfato/farmacología , Adenilil Imidodifosfato/farmacología , Regulación Alostérica , Sitio Alostérico , Animales , Factor Natriurético Atrial/farmacología , Catálisis/efectos de los fármacos , Bovinos , Línea Celular , Membrana Celular/química , Membrana Celular/efectos de los fármacos , Membrana Celular/metabolismo , Guanosina Trifosfato/farmacología , Guanilato Ciclasa/genética , Guanilato Ciclasa/metabolismo , Humanos , Cinética , Ratones , Mutación , Células 3T3 NIH , Péptido Natriurético Tipo-C/farmacología , Receptores del Factor Natriurético Atrial/genética , TransfecciónRESUMEN
Natriuretic peptide receptor A (NPR-A) is an essential cardiovascular regulator that is stimulated by atrial natriuretic peptide and B-type natriuretic peptide, whereas natriuretic peptide receptor B (NPR-B) stimulates long bone growth in a C-type natriuretic peptide-dependent manner. Many reports indicate that ATP is essential for NPR-A and NPR-B activation. Current models suggest that natriuretic peptide binding to receptor extracellular domains causes ATP binding to intracellular kinase homology domains, which derepresses adjacent catalytic domains. Here, we report 100-fold activations of natriuretic peptide receptors in the absence of ATP. The addition of a nonhydrolyzable ATP analog had no effect at early time periods (measured in seconds) but increased cGMP production about 2-fold after longer incubations (measured in minutes), consistent with a stabilization, not activation, mechanism. These data indicate that ATP does not activate natriuretic peptide receptors as has been repeatedly reported. Instead, ATP increases activity primarily by maintaining proper receptor phosphorylation status but also serves a previously unappreciated enzyme stabilizing function.
Asunto(s)
Adenosina Trifosfato/farmacología , Guanilato Ciclasa/metabolismo , Receptores del Factor Natriurético Atrial/metabolismo , Adenosina Trifosfato/análogos & derivados , Animales , Línea Celular , GMP Cíclico/metabolismo , Estabilidad de Enzimas/efectos de los fármacos , Humanos , Cinética , Ratones , Células 3T3 NIH , Fosforilación/efectos de los fármacosRESUMEN
Natriuretic peptide receptor A (NPR-A/GC-A) and B (NPR-B/GC-B) are members of the transmembrane guanylyl cyclase family that mediate the effects of natriuretic peptides via the second messenger, cGMP. Despite numerous reports of these receptors being down-regulated in response to various pathological conditions, no studies have actually measured desensitization and receptor internalization in the same cell line. Furthermore, the ligand-dependent trafficking properties of NPR-A remain controversial, whereas nothing is known about the trafficking of NPR-B. In this report, we tested whether down-regulation explains the ligand-dependent desensitization of NPR-A and NPR-B and characterized their trafficking properties using a combination of hormone-binding and antibody-based assays. Quantitative partition analysis indicated that (125)I-atrial natriuretic peptide (ANP) was rapidly released into the medium after 293T cells stably expressing NPR-A were warmed from 4 degrees to 37 degrees C. High-performance liquid chromatography fractionation of medium supplemented with the protease inhibitor phosphoramidon indicated that the (125)I-ANP was mostly intact. In contrast, (125)I-ANP purified from medium bathing cells expressing NPR-C, a receptor known to internalize natriuretic peptides, was degraded. Cleavable biotinylation and noncleavable biotinylation assays indicated that neither NPR-A nor NPR-B was internalized or degraded in response to natriuretic peptide binding. In contrast, agonist-dependent internalization of a G protein-coupled receptor was clearly apparent in the same cell line. Finally, we show that NPR-A and NPR-B are desensitized in cells in which they are not internalized. We suggest that mechanisms other than receptor down-regulation account for the desensitization of NPR-A and NPR-B that occurs in response to various physiological and pathological stimuli.
Asunto(s)
Regulación hacia Abajo/fisiología , Guanilato Ciclasa/metabolismo , Guanilato Ciclasa/fisiología , Receptores del Factor Natriurético Atrial/fisiología , Factor Natriurético Atrial/farmacocinética , Transporte Biológico , Línea Celular , ADN Complementario , Glicopéptidos/farmacología , Humanos , Radioisótopos de Yodo , Transporte de Proteínas , TransfecciónRESUMEN
C-type natriuretic peptide binding to natriuretic peptide receptor-B (NPR-B) stimulates cGMP synthesis, which regulates vasorelaxation, cell proliferation, and bone growth. Here, we investigated the mechanistic basis for hyperosmotic and lysophosphatidic acid-dependent inhibition of NPR-B. Whole cell cGMP measurements and guanylyl cyclase assays indicated that acute hyperosmolarity decreased NPR-B activity in a reversible, concentration- and time-dependent manner, whereas chronic exposure had no effect. Acute hyperosmolarity elevated intracellular calcium in a concentration-dependent fashion that paralleled NPR-B desensitization. A calcium chelator, but not a protein kinase C inhibitor, blocked both calcium elevations and desensitization. Hyperosmotic medium stimulated NPR-B dephosphorylation, and the receptor was rapidly rephosphorylated and resensitized when the hypertonic media was removed. Lysophosphatidic acid also inhibited NPR-B in a calcium- and phosphorylation-dependent process, consistent with calcium being a universal regulator of NPR-B. The absolute requirement of dephosphorylation in this process was demonstrated by showing that a receptor with glutamates substituted at all known NPR-B phosphorylation sites is unresponsive to hyperosmotic stimuli. This is the first study to measure the phosphorylation state of an endogenous guanylyl cyclase and to link intracellular calcium elevations with its dephosphorylation.