RESUMEN
The extracellular calcium-sensing receptor CaSR is expressed in blood vessels where its role is not completely understood. In this study, we tested the hypothesis that the CaSR expressed in vascular smooth muscle cells (VSMC) is directly involved in regulation of blood pressure and blood vessel tone. Mice with targeted CaSR gene ablation from vascular smooth muscle cells (VSMC) were generated by breeding exon 7 LoxP-CaSR mice with animals in which Cre recombinase is driven by a SM22α promoter (SM22α-Cre). Wire myography performed on Cre-negative [wild-type (WT)] and Cre-positive (SM22α)CaSR(Δflox/Δflox) [knockout (KO)] mice showed an endothelium-independent reduction in aorta and mesenteric artery contractility of KO compared with WT mice in response to KCl and to phenylephrine. Increasing extracellular calcium ion (Ca(2+)) concentrations (1-5 mM) evoked contraction in WT but only relaxation in KO aortas. Accordingly, diastolic and mean arterial blood pressures of KO animals were significantly reduced compared with WT, as measured by both tail cuff and radiotelemetry. This hypotension was mostly pronounced during the animals' active phase and was not rescued by either nitric oxide-synthase inhibition with nitro-l-arginine methyl ester or by a high-salt-supplemented diet. KO animals also exhibited cardiac remodeling, bradycardia, and reduced spontaneous activity in isolated hearts and cardiomyocyte-like cells. Our findings demonstrate a role for CaSR in the cardiovascular system and suggest that physiologically relevant changes in extracellular Ca(2+) concentrations could contribute to setting blood vessel tone levels and heart rate by directly acting on the cardiovascular CaSR.
Asunto(s)
Presión Sanguínea , Señalización del Calcio , Calcio/metabolismo , Hipotensión/metabolismo , Músculo Liso Vascular/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Vasoconstricción , Vasodilatación , Animales , Aorta/metabolismo , Presión Sanguínea/efectos de los fármacos , Presión Sanguínea/genética , Bradicardia/genética , Bradicardia/metabolismo , Bradicardia/fisiopatología , Señalización del Calcio/efectos de los fármacos , Señalización del Calcio/genética , Relación Dosis-Respuesta a Droga , Predisposición Genética a la Enfermedad , Frecuencia Cardíaca , Hipotensión/genética , Hipotensión/fisiopatología , Arterias Mesentéricas/metabolismo , Ratones de la Cepa 129 , Ratones Endogámicos C57BL , Ratones Noqueados , Músculo Liso Vascular/efectos de los fármacos , Músculo Liso Vascular/fisiopatología , Miocitos Cardíacos/metabolismo , Fenotipo , Receptores Sensibles al Calcio , Receptores Acoplados a Proteínas G/deficiencia , Receptores Acoplados a Proteínas G/genética , Vasoconstricción/efectos de los fármacos , Vasoconstricción/genética , Vasoconstrictores/farmacología , Vasodilatación/efectos de los fármacos , Vasodilatación/genética , Vasodilatadores/farmacología , Remodelación VentricularRESUMEN
Atrial myocytes in a number of species lack transverse tubules. As a consequence the intracellular calcium signals occurring during each heartbeat exhibit complex spatio-temporal dynamics. These calcium patterns arise from saltatory calcium waves that propagate via successive rounds of diffusion and calcium-induced calcium release. The many parameters that impinge on calcium-induced calcium release and calcium signal propagation make it difficult to know a priori whether calcium waves will successfully travel, or be extinguished. In this study, we describe in detail a mathematical model of calcium signalling that allows the effect of such parameters to be independently assessed. A key aspect of the model is to follow the triggering and evolution of calcium signals within a realistic three-dimensional cellular volume of an atrial myocyte, but with low computational costs. This is achieved by solving the linear transport equation for calcium analytically between calcium release events and by expressing the onset of calcium liberation as a threshold process. The model makes non-intuitive predictions about calcium signal propagation. For example, our modelling illustrates that the boundary of a cell produces a wave-guiding effect that enables calcium ions to propagate further and for longer, and can subtly alter the pattern of calcium wave movement. The high spatial resolution of the modelling framework allows the study of any arrangement of calcium release sites. We demonstrate that even small variations in randomly positioned release sites cause highly heterogeneous cellular responses. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.
Asunto(s)
Señalización del Calcio/fisiología , Modelos Cardiovasculares , Miocitos Cardíacos/metabolismo , Atrios Cardíacos/citología , Atrios Cardíacos/metabolismo , Humanos , Miocitos Cardíacos/citologíaRESUMEN
Herein, we report the synthesis and characterization of nanospheres of a biodegradable zinc-imidazolate polymers (ZIPs) as a proof-of-concept delivery vehicle into human brain endothelial cells, the main component of the blood-brain barrier (BBB). The ZIP particles can readily encapsulate functional molecules such as fluorophores and inorganic nanoparticles at the point of synthesis producing stable colloidal dispersions. Our results show that these biodegradable particles are not cytotoxic, and are able to penetrate and release cargo species to human brain capillary endothelial cells in vitro thus exhibiting significant potential as a novel platform for brain targeting treatments.
RESUMEN
The salivary glands in the cockroach Periplaneta americana secrete protein-containing saliva when stimulated by serotonin (5-HT) and protein-free saliva upon dopamine stimulation. In order to obtain information concerning the signalling pathways involved in 5-HT-induced protein secretion, we have determined the protein content of saliva secreted after experimental manipulations that potentially elevate intracellular Ca2+ and cyclic nucleotide concentrations in isolated glands. We have found that 5-HT stimulates the rate of protein secretion in a dose-dependent manner (threshold: 3 x 10(-8)M; EC50 1.5 x 10(-6)M). The maximal rate of 5-HT-induced protein secretion was 2.2 +/- 0.2 microg/min. Increasing intracellular Ca2+ or cAMP by bath application of ionomycin (5 microM), db cAMP (10mM), forskolin (100 microM) or IBMX (100 microM), respectively, stimulated protein secretion at significantly lower rates, whereas db cGMP (1mM) did not activate protein secretion. The high rates and the kinetics of 5-HT-induced protein secretion could only be mimicked by either applying forskolin together with IBMX (with or without ionomycin) or by applying IBMX together with ionomycin. Our measurements suggest that 5-HT-induced protein secretion is mediated by an elevation of [cAMP]i and that Ca2+ may function as a co-agonist and augment the rate of protein secretion.
Asunto(s)
Calcio/metabolismo , AMP Cíclico/metabolismo , Proteínas de Insectos/metabolismo , Periplaneta/fisiología , Glándulas Salivales/metabolismo , Proteínas y Péptidos Salivales/metabolismo , 1-Metil-3-Isobutilxantina/farmacología , Animales , Bucladesina/farmacología , Colforsina/farmacología , Dopamina/fisiología , Relación Dosis-Respuesta a Droga , Iminas/farmacología , Ionomicina/farmacología , Ionóforos/farmacología , Masculino , Periplaneta/metabolismo , Inhibidores de Fosfodiesterasa/farmacología , Glándulas Salivales/efectos de los fármacos , Serotonina/farmacologíaRESUMEN
Isolated salivary glands of Periplaneta americana were used to measure secretion rates and, by quantitative capillary electrophoresis, Na(+), K(+), and Cl(-) concentrations in saliva collected during dopamine (1 micro M) and serotonin (1 micro M) stimulation in the absence and presence of ouabain (100 micro M) or bumetanide (10 micro M). Dopamine stimulated secretion of a NaCl-rich hyposmotic saliva containing (mM): Na(+) 95 +/- 2; K(+) 38 +/- 1; Cl(-) 145 +/- 3. Saliva collected during serotonin stimulation had a similar composition. Bumetanide decreased secretion rates induced by dopamine and serotonin; secreted saliva had lower Na(+), K(+) and Cl(-) concentrations and osmolarity. Ouabain caused increased secretion rates on a serotonin background. Saliva secreted during dopamine but not serotonin stimulation in the presence of ouabain had lower K(+) and higher Na(+) and Cl(-) concentrations, and was isosmotic. We concluded: The Na(+)-K(+)-2Cl(-) cotransporter is of cardinal importance for electrolyte and fluid secretion. The Na(+)/K(+)-ATPase contributes to apical Na(+) outward transport and Na(+) and K(+) cycling across the basolateral membrane in acinar P-cells. The salivary ducts modify the primary saliva by Na(+) reabsorption and K(+) secretion, whereby Na(+) reabsorption is energized by the basolateral Na(+)/K(+)-ATPase which imports also some of the K(+) needed for apical K(+) extrusion.