DSpace Repository :: Browsing by Author "Martínez, Agustín"

Browsing by Author "Martínez, Agustín"

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Carbon monoxide: A new player in the redox regulation of connexin hemichannels
(International Union of Biochemistry and Molecular Biology, 2015) Retamal, Mauricio; León-Paravic, Carmen; Ezquer, Marcelo; Ezquer, Fernando; Del Río, Rodrigo; Pupo, Amaury; Martínez, Agustín; González, Carlos
Carbon monoxide (CO) is a gaseous transmitter that is known to be involved in several physiological processes, but surprisingly it is also becoming a promising molecule to treat several pathologies including stroke and cancer. CO can cross the plasma membrane and activate guanylate cyclase, increasing the cGMP concentration and activating some kinases, including PKG. The other mechanism of action involves induction of protein carbonylation. CO is known to directly and indirectly modulate the function of ion channels at the plasma membrane, which in turn have important repercussions in the cellular behavior. One group of these channels is hemichannels, which are formed by proteins known as connexins (Cxs). Hemichannel allows not only the flow of ions through their pore but also the release of molecules such as ATP and glutamate. Therefore, their modulation not only impacts cellular function but also cellular communication, having the capability to affect tissular behavior. Here, we review the most recent results regarding the effect of CO on Cx hemichannels and their possible repercussions on pathologies.
Charged Residues at the First Transmembrane Region Contribute to the Voltage Dependence of the Slow Gate of Connexins
(American Society for Biochemistry and Molecular Biology by Sage, 2016) Pinto, Bernardo; García, Isaac; Pupo, Amaury; Retamal, Mauricio; Martínez, Agustín; Latorre, Ramón; González, Carlos
Connexins (Cxs) are a family of membrane-spanning proteins that form gap junction channels and hemichannels. Connexin-based channels exhibit two distinct voltage-dependent gating mechanisms termed slow and fast gating. Residues located at the C terminus of the first transmembrane segment (TM-1) are important structural components of the slow gate. Here, we determined the role of the charged residues at the end of TM-1 in voltage sensing in Cx26, Cx46, and Cx50. Conductance/voltage curves obtained from tail currents together with kinetics analysis reveal that the fast and slow gates of Cx26 involves the movement of two and four charges across the electric field, respectively. Primary sequence alignment of different Cxs shows the presence of well conserved glutamate residues in the C terminus of TM-1; only Cx26 contains a lysine in that position (lysine 41). Neutralization of lysine 41 in Cx26 increases the voltage dependence of the slow gate. Swapping of lysine 41 with glutamate 42 maintains the voltage dependence. In Cx46, neutralization of negative charges or addition of a positive charge in the Cx26 equivalent region reduced the slow gate voltage dependence. In Cx50, the addition of a glutamate in the same region decreased the voltage dependence, and the neutralization of a negative charge increased it. These results indicate that the charges at the end of TM-1 are part of the slow gate voltage sensor in Cxs. The fact that Cx42, which has no charge in this region, still presents voltage-dependent slow gating suggests that charges still unidentified also contribute to the slow gate voltage sensitivity.
Contribution of Connexin Hemichannels to the Decreases in Cell Viability Induced by Linoleic Acid in the Human Lens Epithelial Cells (HLE-B3)
(2019) Figueroa, Vania; Jara, Oscar; Oliva, Carolina; Ezquer, Marcelo; Ezquer, Fernando; Retamal, Mauricio; Martínez, Agustín; Altenberg, Guillermo; Vargas, Aníbal
Connexin (Cx) proteins form hemichannels that a allow bidirectional flow of ions and metabolites between the cytoplasm and extracellular space. Under physiological conditions, hemichannels have a very low probability of opening, but in certain pathologies, hemichannels activity can increase and induce and/or accelerate cell death. Several mechanisms control hemichannels activity, including phosphorylation and oxidation (i.e., S-nitrosylation). Recently, the effect of polyunsaturated fatty acids (PUFAs) such as linoleic acid (LA), were found to modulate Cxs. It has been seen that LA increase cell death in bovine and human lens cells. The lens is a structure allocated in the eye that highly depends on Cx for the metabolic coupling between its cells, a condition necessary for its transparency. Therefore, we hypothesized that LA induces lens cells death by modulating hemichannel activity. In this work, we characterized the effect of LA on hemichannel activity and survival of HLE-B3 cells (a human lens epithelial cell line). We found that HLE-B3 cells expresses Cx43, Cx46, and Cx50 and can form functional hemichannels in their plasma membrane. The extracellular exposure to 10–50 μM of LA increases hemichannels activity (dye uptake) in a concentration-dependent manner, which was reduced by Cx-channel blockers, such as the Cx-mimetic peptide Gap27 and TATGap19, La3+, carbenoxolone (CBX) and the Akt kinase inhibitor. Additionally, LA increases intracellular calcium, which is attenuated in the presence of TATGap19, a specific Cx43-hemichannel inhibitor. Finally, the long exposure of HLE-B3 cells to LA 20 and 50 μM, reduced cell viability, which was prevented by CBX. Moreover, LA increased the proportion of apoptotic HLE-B3 cells, effect that was prevented by the Cx-mimetic peptide TAT-Gap19 but not by Akt inhibitor. Altogether, these findings strongly suggest a contribution of hemichannels opening in the cell death induced by LA in HLE-B3 cells. These cells can be an excellent tool to develop pharmacological studies in vitro.
Extracellular gentamicin reduces the activity of con nexin hemichannels and interferes with purinergic Ca2+ signaling in HeLa cells
(Frontiers Research Foundation, 2014) Figueroa, Vania; Retamal, Mauricio; Cea, Luis; Salas, José; Vargas, Aníbal; Verdugo, Christián; Jara, Oscar; Martínez, Agustín; Sáez, Juan
Gap junction channels (GJCs) and hemichannels (HCs) are composed of protein subunits termed connexins (Cxs) and are permeable to ions and small molecules. In most organs, GJCs communicate the cytoplasm of adjacent cells, while HCs communicate the intra and extracellular compartments. In this way, both channel types coordinate physiological responses of cell communities. Cx mutations explain several genetic diseases, including about 50% of autosomal recessive non-syndromic hearing loss. However, the possible involvement of Cxs in the etiology of acquired hearing loss remains virtually unknown. Factors that induce post-lingual hearing loss are diverse, exposure to gentamicin an aminoglycoside antibiotic, being the most common. Gentamicin has been proposed to block GJCs, but its effect on HCs remains unknown. In this work, the effect of gentamicin on the functional state of HCs was studied and its effect on GJCs was reevaluated in HeLa cells stably transfected with Cxs. We focused on Cx26 because it is the main Cx expressed in the cochlea of mammals where it participates in purinergic signaling pathways. We found that gentamicin applied extracellularly reduces the activity of HCs, while dye transfer across GJCs was not affected. HCs were also blocked by streptomycin, another aminoglycoside antibiotic. Gentamicin also reduced the adenosine triphosphate release and the HC-dependent oscillations of cytosolic free-Ca2+ signal. Moreover, gentamicin drastically reduced the Cx26 HC-mediated membrane currents in Xenopus laevis oocytes. Therefore, the extracellular gentamicin-induced inhibition of Cx HCs may adversely affect autocrine and paracrine signaling, including the purinergic one, which might partially explain its ototoxic effects.
Percepción de los apoderados sobre la salud visual de niños del jardín infantil institucional de Gendarmería de Chile
(Facultad de Medicina Clínica Alemana Universidad del Desarrollo, 2020) Arbat, Catalina; Conrads, Benjamín; Hernández, Javiera; Martínez, Agustín
Introducción: La visión es fundamental para el desarrollo humano. Existen alteraciones visuales reversibles si son tratadas tempranamente. De lo contrario, la pérdida de visión puede ser irrecuperable. En ello radica la importancia del control oftalmológico temprano, sin embargo, los apoderados acuden a él de manera tardía. Se hipotetiza que esto ocurre debido a que no perciben los signos y síntomas de las alteraciones visuales de sus niños. Objetivo: Determinar si los apoderados perciben los signos y síntomas visuales de los niños. Metodología: participaron apoderados de niños no diagnosticados previamente al screening, entre 2 a 5 años, del Jardín Infantil de Gendarmería. Se les aplicó un cuestionario que evaluó la percepción de estos sobre la salud visual de los niños, para compararla con en su screening oftalmológico. Para el análisis, se utilizó el estadístico exacto de Fisher, con 95% de confianza. Resultado: 18 cuestionarios fueron respondidos, en los que se señaló percepción de 21% y 25% de los apoderados de niños con ausencia y presencia de alteraciones visuales, respectivamente. No existe relación entre la presencia de alguna alteración visual y la percepción de los signos y síntomas por parte de los apoderados, ambas variables se comportan independientemente. Discusión: La mayoría de los apoderados no tienen percepción de alteraciones visuales en los niños. Además, las alteraciones visuales en un niño no determinan, ni condicionan, la percepción de los apoderados, lo que es compatible con la consulta tardía al oftalmólogo. Conclusión: la existencia de una alteración visual del niño no determina la percepción de sus apoderados.

Browsing by Author "Martínez, Agustín"

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