RESUMEN
Angiotensin II (AngII) is the final active product of the renin enzymatic cascade, which is responsible for sustaining blood pressure. To investigate the effect of N-terminal cyclization on AT1 activation and tachyphylaxis, we designed conformationally constrained analogues with an i-(i + 1) lactam bridge. All analogues presented the same binding coefficient and tachyphylactic index, but some of them such as Cyclo (0-1a) [Glu0 , endo-(Lys1a )]-AngII and Cyclo (0-1a) [Asp0 , endo-(Orn1a )]-AngII showed higher potency. The same tachyphylactic index presented by AngII and cyclic analogues was surprising. We expected a variation after the modification of AngII N-terminal region.
Asunto(s)
Angiotensina II/análogos & derivados , Lactamas/química , Receptor de Angiotensina Tipo 1/metabolismo , Secuencia de Aminoácidos , Angiotensina II/síntesis química , Angiotensina II/metabolismo , Angiotensina II/farmacología , Animales , Células CHO , Dicroismo Circular , Cricetinae , Cricetulus , Ciclización , Fundus Gástrico/efectos de los fármacos , Fundus Gástrico/fisiología , Ligandos , Ratones , Ratones Endogámicos C57BL , Péptidos/síntesis química , Péptidos/química , Péptidos/farmacología , Unión Proteica , Estructura Secundaria de Proteína , Receptor de Angiotensina Tipo 1/química , Receptor de Angiotensina Tipo 1/genética , Taquifilaxis/fisiologíaRESUMEN
Tachyphylaxis, defined as the acute loss of response of some smooth muscles upon repeated stimulations with angiotensin II (Ang II), has been shown to be dependent mainly on the N-terminal region of the ligand. To further study the structural requirements for the induction of tachyphylaxis we have synthesized Ang II analogs containing the bulky and very lipophilic substituents 9-fluorenylmethyloxycarbonyl (Fmoc) and 9-fluorenylmethyl ester (OFm) at the alpha-amino (Nalpha-Fmoc-Ang II) or the beta-carboxyl ([Asp(OFm)1]-Ang II) groups of the Asp1 residue, respectively. In binding assays with Chinese hamster ovary cells transfected with the AT1 Ang II receptor, Nalpha-Fmoc-Ang II bound with high affinity, whereas [Asp(OFm)1]-Ang II showed lower affinity. In biological assays, these two analogs were full agonists and showed 30 and 3%, respectively, of the Ang II potency in contracting the guinea-pig ileum smooth muscle. The two analogs induced tachyphylaxis, in spite of the lack of a free amino group in Nalpha-Fmoc-Ang II. Thus, analogs with Fmoc- or OFm-type groups coupled to the Asp1 residue, whether at the amino or carboxyl functions, induce tachyphylaxis through an unreported mechanism. Based in these findings and those available from the literature, an alternate molecular interaction mode between Ang II N-terminal portion and the AT1 receptor is proposed to explain the tachyphylactic phenomenon.
Asunto(s)
Angiotensina II/análogos & derivados , Oligopéptidos/farmacología , Receptor de Angiotensina Tipo 1/efectos de los fármacos , Taquifilaxis/fisiología , Angiotensina II/farmacología , Animales , Unión Competitiva , Células CHO , Cricetinae , Relación Dosis-Respuesta a Droga , Femenino , Cobayas , Interacciones Hidrofóbicas e Hidrofílicas , Íleon/efectos de los fármacos , Técnicas In Vitro , Contracción Muscular/efectos de los fármacos , Músculo Liso/efectos de los fármacos , Oligopéptidos/síntesis química , Ensayo de Unión Radioligante , Relación Estructura-ActividadRESUMEN
We have previously demonstrated that Chinese hamster ovary (CHO) cells transfected with the angiotensin II AT1 receptor gene containing only the coding region, presented tachyphylaxis to the total inositol phosphate (InsPs) and Ca2+ responses mediated by angiotensin II and [2-lysine]angiotensin II ([Lys2]angiotensin II). Now we have evaluated the possible role of the 3'-untranslated region of the angiotensin AT1 receptor mRNA in modulating the angiotensin AT1 receptor-mediated cellular responses. The binding parameters, as well as the Ca2+ and InsPs responses induced by angiotensin II and [Lys2]angiotensin II were similar in cells transfected with the angiotensin AT1 receptor with or without the 3'-untranslated region sequence. In cells transfected with the receptor containing the 3'-untranslated region sequence, angiotensin II-induced Ca2+ and InsPs responses were desensitized by repeated stimulations, whereas [Lys2]angiotensin II caused desensitization of InsPs production but not of Ca2+ uptake in these cells. Our results suggest that the 3'-untranslated region plays a role in modulating cell signalling involved in the tachyphylaxis of angiotensin AT1 receptor-mediated Ca2+ responses.
Asunto(s)
Regiones no Traducidas 3'/fisiología , Angiotensina II/análogos & derivados , Angiotensina II/metabolismo , Receptor de Angiotensina Tipo 1/fisiología , Angiotensina II/farmacología , Animales , Sitios de Unión , Células CHO , Calcio/metabolismo , Cricetinae , Fosfatos de Inositol/biosíntesis , Ratas , Receptor de Angiotensina Tipo 1/genética , Receptor de Angiotensina Tipo 1/metabolismo , Taquifilaxis/genética , Taquifilaxis/fisiología , TransfecciónRESUMEN
The manifestation of tachyphylaxis to angiotensin II in Chinese hamster ovary (CHO) cells expressing the rat angiotensin II AT(1) receptor was investigated. The cells were transfected with a cDNA fragment containing the complete coding region of the angiotensin II AT(1A) receptor gene, as well as 56 bp of its 3'- and 52 bp of its 5'-untranslated regions. These cells (CHO-AT(1)) responded to angiotensin II by increases in intracellular Ca(2+) concentration and inositol phosphate turnover, which were inhibited upon repeated administrations, characterizing the tachyphylaxis phenomenon. In contrast to smooth muscle cells, which are rendered tachyphylactic to angiotensin II but not to [2-lysine]angiotensin II ([Lys(2)]angiotensin II), this analogue induced responses in CHO-AT(1) cells that were also inhibited upon repeated administrations. A smooth muscle cell line, which showed tachyphylaxis only to angiotensin II, became tachyphylactic also to [Lys(2)]angiotensin II after transfection with the angiotensin II AT(1) receptor gene. Our findings suggest that posttranscriptional control directed by the 3'- or the 5'-untranslated regions in the angiotensin II AT(1) receptor gene may play a role in modulating the signal transduction pathways involved in the mechanism of angiotensin II tachyphylaxis.
Asunto(s)
Angiotensina II/análogos & derivados , Receptores de Angiotensina/fisiología , Taquifilaxis/fisiología , Adenosina Trifosfato/farmacología , Angiotensina II/farmacología , Animales , Células CHO , Calcio/metabolismo , Cricetinae , ADN Recombinante/genética , Expresión Génica , Glicina/farmacología , Fosfatos de Inositol/metabolismo , Soluciones Isotónicas/farmacología , Músculo Liso Vascular/citología , Músculo Liso Vascular/efectos de los fármacos , Músculo Liso Vascular/metabolismo , Conejos , Ratas , Receptor de Angiotensina Tipo 1 , Receptores de Angiotensina/efectos de los fármacos , Receptores de Angiotensina/genética , TransfecciónRESUMEN
The importance of residues 9 and 10 in endothelin-1 was assessed by studying the responses of the guinea-pig ileum to [Ala9]endothelin-1 and [Ala10]endothelin-1. Both analogues induced relaxation followed by contraction. [Ala9]Endothelin-1 showed similar ED50 values and maximum response to those of endothelin-1, whereas [Ala10]endothelin-1 showed a larger ED50 value and was a partial agonist. Endothelin-1 and [Ala10]endothelin-1 induced similar degrees of tachyphylaxis, whereas [Ala9]endothelin-1 induced very little tachyphylaxis, indicating that Lys9 is important for inducing tachyphylaxis. Apamin inhibited the relaxation induced by endothelin-1 and [Ala9]endothelin-1 but not that induced by [Ala10]endothelin-1. BQ-123 (cyclo[D-Trp-D-Asp-Pro-D-Val-Leu), a specific endothelin ETA receptor antagonist, inhibited [Ala9]endothelin-1-, but not [Ala10]endothelin-1-induced contraction. Cross-tachyphylaxis and additivity studies indicated that [Ala9]endothelin-1, like endothelin-1, acts at the endothelin ETA receptor, whereas [Ala10]endothelin-1 behaved as an endothelin ETB receptor agonist, like sarafotoxin S6c. Thus, the residue at position 10 plays a significant role in receptor activation and is a candidate for further exploration of receptor antagonism.
Asunto(s)
Endotelinas/química , Endotelinas/farmacología , Receptores de Endotelina/efectos de los fármacos , Secuencia de Aminoácidos , Animales , Apamina/farmacología , Antagonistas de los Receptores de Endotelina , Endotelina-1/análogos & derivados , Femenino , Cobayas , Íleon/efectos de los fármacos , Técnicas In Vitro , Contracción Isométrica/efectos de los fármacos , Contracción Isotónica/efectos de los fármacos , Masculino , Datos de Secuencia Molecular , Contracción Muscular/efectos de los fármacos , Péptidos Cíclicos/farmacología , Receptores de Endotelina/agonistas , Sodio/metabolismo , Taquifilaxis/fisiologíaAsunto(s)
Humanos , Asma/tratamiento farmacológico , Broncodilatadores/farmacología , Espasmo Bronquial/tratamiento farmacológico , Broncodilatadores/efectos adversos , Sistema Nervioso Central/efectos de los fármacos , Hipopotasemia/etiología , Simpatomiméticos/metabolismo , Taquifilaxis/fisiologíaRESUMEN
1. In the guinea-pig ileum the C-terminal hexapeptide of the endothelins, endothelin (16-21), induced a biphasic effect (relaxation followed by contraction) qualitatively similar to that seen in the responses to endothelins 1 and 3. Both components of the response were concentration-dependent in the range studied (2-100 microM). 2. The response induced by endothelin (16-21) was inhibited in low-sodium (80 mM) medium. 3. Repeated administration of endothelin (16-21) induced no desensitization of the preparation, contrasting with the tachyphylaxis induced by endothelin-1 and endothelin-3 in the guinea-pig ileum. 4. Tissues rendered tachyphylatic to endothelin-1 or endothelin-3 responded normally to endothelin (16-21). 5. The results suggest that the C-terminal tail of the endothelins contains the message for the biphasic response, whereas the N-terminal domain may be responsible for the strong binding to the receptor and for the tachyphylactic properties of endothelin-1 and endothelin-3, in the guinea-pig isolated ileum. However, the possibility that endothelin (16-21) may be acting on a site other than the endothelin receptor cannot be ruled out.
Asunto(s)
Endotelinas/farmacología , Músculo Liso/efectos de los fármacos , Fragmentos de Péptidos/farmacología , Secuencia de Aminoácidos , Animales , Femenino , Cobayas , Íleon/efectos de los fármacos , Técnicas In Vitro , Contracción Isométrica/efectos de los fármacos , Masculino , Datos de Secuencia Molecular , Receptores de Endotelina/efectos de los fármacos , Sodio/fisiología , Taquifilaxis/fisiologíaRESUMEN
Simultaneous recordings of the tension and intracellular Ca2+ concentration of guinea-pig ileum longitudinal smooth muscle strips, as well as 24Na+ and 45Ca2+ influx measurements in cultured myocytes from the same tissue, were used to investigate the mechanisms underlying angiotensin-induced desensitization and tachyphylaxis. Angiotensin II and [2-lysine]-angiotensin II (Lys2All), incubated for prolonged periods (10 min) with muscle strips, induced fading of the contractile response (desensitization) and reappearance of the intracellular Ca2+ concentration oscillations, which were inhibited during the initial increase in cytosolic Ca2+. The desensitization was paralleled, in cultured myocytes, by inhibition of the 45Ca2+ but not of the 24Na+ influxes which were initially stimulated by the peptides. On the other hand, repeated administrations of angiotensin II (but not of Lys2All) caused gradual reduction of the contractile response and of the 24Na+ influx stimulation evoked by the agonist (tachyphylaxis). Treatment with phorbol 12-13 dibutyrate accelerated the desensitization induced by both angiotensin II and by Lys2All and aggravated the tachyphylaxis to angiotensin II. The results support the hypothesis that activation of protein kinase C is responsible for the desensitization and that tachyphylaxis is due to the slow dissociation of angiotensin II from a postulated Na(+)-dependent regulatory site on the receptor.
Asunto(s)
Angiotensina II/farmacología , Íleon/efectos de los fármacos , Contracción Muscular/efectos de los fármacos , Proteína Quinasa C/fisiología , Sodio/fisiología , Taquifilaxis/fisiología , Animales , Calcio/metabolismo , Células Cultivadas , Femenino , Cobayas , Masculino , Contracción Muscular/fisiología , Forbol 12,13-Dibutirato/farmacología , Sodio/metabolismoRESUMEN
Normal and alloxan treated diabetic rabbit kidneys were perfused with Krebs-Henseleit solution in a non-recirculating system and the effects of norepinephrine (NOR) 10(-6)M were tested by infusion of this drug for three subsequent periods of 20 min each, with an interval of 10 min for drug wash-out. In the control kidneys the infusion of NOR promoted an intense vasoconstriction, which was less intense during the second and the third periods. This was known as tachyphylaxis. In contrast to the controls, kidneys from diabetic animals did not show tachyphylaxis to NOR, but when insulin was added to the perfusate, tachyphylaxis appeared. Normal kidneys perfused with hyperosmolar solutions show, as in controls, the same phenomenon. The data presented here demonstrate a defect of adrenergic vascular receptors in alloxan treated kidneys, which can be acutely reversed by insulin. These facts are of importance for the understanding of the vascular disease in diabetes.