VALIDACIÓN NUMÉRICA Y EXPERIMENTAL DE UN ARO DE FIJACIÓN EXTERNA ILIZAROV PARA FRACTURAS

La validación numérica de sistemas biomecánicos sigue siendo un tema de interés. Por lo anterior, este trabajo tiene como objetivo determinar y analizar el comportamiento mecánico del sistema de fijación externa circular Ilizarov (F.E.C) y su validación numérica por M.E.F con resultados de pruebas experimentales por extensometria basadas en ASTM F-1541-02 A.3 (Standard Specification and Test Methods for External Skeletal Fixation Device) [1], en donde previamente se fabricaron probetas en base a ASTM-E8M [3]. A través de este trabajo se obtuvieron el diagrama fuerza-deformación de la prueba experimental, por medio de un  sistema adquisitor, utilizando extensometria con strain-gages [2], y se compararon los resultados contra un análisis numérico del tipo multi-lineal isotrópico, Los resultados presentan una comparación entre los resultados por simulación numérica y experimental, se muestran  la rigidez, curvas de fuerza versus desplazamiento,  esfuerzo y fuerza versus deformación unitaria, en donde se obtuvo  el diagrama fuerza- desplazamiento, con una fuerza al punto de fluencia de 1800 N, con su respectivo desplazamiento de 3.4 mm, de lo que se calcula la rigidez del fijador y se obtiene el valor de 530 N/mm, con lo cual , se excede el criterio interno T.D.I, el cual define parámetros de rigidez y fuerza para la aceptación de dispositivos médicos, la simulación del aro y su validación son parte de las pruebas requeridas por la COFEPRIS, para la regulación sanitaria correspondiente a pruebas biomecánicas en dispositivos médicos.Este trabajo permitió observar los efectos estructurales del aro de fijación externa de manera experimental y la validación de su modelo numérico. Adicionalmente se lograron simular las no-linealidades por contacto en la región de unión del aro, obteniendo buenos resultados no solo cualitativos, si no también cuantitativos. Finalmente, los resultados obtenidos en este trabajo permitirán simular de manera confiable, el sistema completo de fijación externa circular Ilizarov y con ello tener un modelo numérico completo de este sistema para estudios e investigación posteriores.Palabra(s) Clave(s): F.E.C. Ilizarov, Aro, Strain-gage, Traumatología por osteosíntesis, Prueba de compresión, Elemento finito

Probing the bradycardic drug binding receptor of HCN-encoded pacemaker channels

If (or Ih), encoded by the hyperpolarization-activated, cyclic nucleotide-gated (HCN1–4) channel gene family, contributes significantly to cardiac pacing. Bradycardic agents such as ZD7288 that target HCN channels have been developed, but the molecular configuration of their receptor is poorly defined. Here, we probed the drug receptor by systematically introducing alanine scanning substitutions into the selectivity filter (C347A, I348A, G349A, Y350A, G351A in the P-loop), outer (P355A, V356A, S357A, M358A in the P-S6 linker), and inner (M377A, F378A, V379A in S6) pore vestibules of HCN1 channels. When heterologously expressed in human embryonic kidney 293 cells for patch-clamp recordings, I348A, G349A, Y350A, G351A, P355A, and V356A did not produce measurable currents. The half-blocking concentration (IC50) of wild type (WT) for ZD7288 was 25.8 ± 9.7 μM. While the IC50 of M358A was identical to WT, those of C347A, S357A, F378A, and V379A markedly increased to 137.6 ± 56.4, 113.3 ± 34.1, 587.1 ± 167.5, and 1726.3 ± 673.4 μM, respectively (p < 0.05). Despite the proximity of the S6 residues studied, M377A was hypersensitive (IC50 = 5.1 ± 0.7 μM; p < 0.05) implicating site specificity. To explore the energetic interactions among the S6 residues, double and triple substitutions (M377A/F378A, M377A/V379A, F378A/V379A, and M377A/F378A/V379A) were generated for thermodynamic cycle analysis. Specific interactions with coupling energies (ΔΔG) >1 kT for M377–F378 and F378–V379 but not M377–V379 were identified. Based on these new data and others, we proposed a refined drug-blocking model that may lead to improved antiarrhythmics and bioartificial pacemaker designs

Helical secondary structure of the external S3-S4 linker of pacemaker (HCN) channels revealed by site-dependent perturbations of activation phenotype

If, encoded by the hyperpolarization-activated cyclic nucleotide-modulated channel family (HCN1-4), contributes significantly to neuronal and cardiac pacing. Recently, we reported that the S3-S4 residue Glu-235 of HCN1 influences activation by acting as a surface charge. However, it is uncertain whether other residues of the external S3-S4 linker are also involved in gating. Furthermore, the secondary conformation of the linker is not known. Here we probed the structural and functional role of the HCN1 S3-S4 linker by introducing systematic mutations into the entire linker (defined as 229-237) and studying their effects. We found that the mutations K230A (-62.2 ± 3.4 mV versus -72.2 ± 1.7 mV of wild type (WT)), G231A (-64.4 ± 1.3 mV), M232A (V1/2 = -63.1 ± 1.1 mV), and E235G (-65.4 ± 1.5 mV) produced depolarizing activation shifts. Although E229A and M232A decelerated gating kinetics ( 0.05). Shortening the linker (EVY235-237ΔΔΔ) caused depolarizing activation shift and slowed kinetics that could not be explained by removing the charge at position 235 alone. Secondary structural predictions by the modeling algorithms SSpro2 and PROF, along with refinements by our experimental data, suggest that part of the S3-S4 linker conforms a helical structure with the functionally important residues Met-232, Glu-235, and Gly-231 (|ΔΔG|>1 kcal/mol) clustered on one side.link_to_subscribed_fulltex

Critical intra-linker interactions of HCN1-encoded pacemaker channels revealed by interchange of S3-S4 determinants

Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels contribute to the spontaneous rhythmic activities in cardiac and neuronal cells. Recently, we reported that the S3-S4 linker of HCN1 channels influences activation, and that part of the linker is helical with the determinants G231, M232, and E235 clustered on one side. Here we explored the undefined role of the G 231E 235M 232 triplet by systematic substitutions. Replacing G231 or M232 next to the "neighboring" E235 in the S3-S4 helix with an anionic residue (i.e., G231E, M232E) rendered channels non-functional although they were localized on the membrane surface. Interestingly, this loss of function could be readily rescued either by introducing a countercharge at position 235 (G231E/E235R, M232E/E235R) or by interchanging residues 231 or 232 and 235 (G231E/E235G, M232E/E235M). We conclude that residues 231, 232, and 235 are in close spatial proximity to each other, and uniquely interact with one another to shape the phenotypes of HCN channels. © 2004 Elsevier Inc. All rights reserved.link_to_subscribed_fulltex

Dissecting the structural and functional roles of the S3-S4 linker of pacemaker (hyperpolarization-activated cyclic nucleotide-modulated) channels by systematic length alterations

I f or I h, a key player in neuronal and cardiac pacing, is encoded by the hyperpolarization-activated cyclic nucleotide-modulated (HCN) channel gene family. We have recently reported that the S3-S4 linker (i.e. residues 229EKGMDSEVY 237 of HCN1) prominently influences the activation phenotypes of HCN channels and that part of the linker may conform a secondary helical structure. Here we further dissected the structural and functional roles of this linker by systematic alterations of its length. In contrast to voltage-gated K + channels, complete deletion of the S3-S4 linker (Δ229-237) did not produce functional channels. Similarly, the deletions Δ229-234, Δ232-234, and Δ232-237 also abolished normal current activity. Interestingly, Δ229-231, Δ233-237, Δ234-237, Δ235-237, Δ229-231/Δ233-237, Δ229-231/Δ234-237, and Δ229-231/Δ235-237 all yielded robust hyperpolarization-activated inward currents, indicating that loss-of-function caused by deletion could be rescued by keeping the single functionally important residue Met 232 alone. Whereas shortening the linker by deletion generally shifted steady-state activation in the depolarizing direction (e.g. ΔV 1/2 of Δ229-231, Δ233-237, Δ235-237 >+10 mV relative to wild type), linker prolongation by duplicating the entire linker (Dup229-237) or by glutamine insertion (InsQ233Q, InsQQ233QQ and InsQQQ233QQQ, or Ins237QQQ) produced length-dependent progressive hyperpolarizing activation shifts (-35 mV < ΔV 1/2 < -4 mV). Based on these results, we conclude that only Met 232 is prerequisite for channels to function, but the length and other constituents of the S3-S4 linker shape the ultimate activation phenotype. Our results also highlight several evolutionary similarities and differences between HCN and voltage-gated K + channels. Manipulations of the S3-S4 linker length may provide a flexible approach to customize HCN gating for engineering electrically active cells (such as stem cell-derived neuronal and cardiac pacemakers) for gene- and cell-based therapies.link_to_subscribed_fulltex

Dissecting the structural and functional roles of the S3-S4 linker of pacemaker (hyperpolarization-activated cyclic nucleotide-modulated) channels by systematic length alterations

I f or I h, a key player in neuronal and cardiac pacing, is encoded by the hyperpolarization-activated cyclic nucleotide-modulated (HCN) channel gene family. We have recently reported that the S3-S4 linker (i.e. residues 229EKGMDSEVY 237 of HCN1) prominently influences the activation phenotypes of HCN channels and that part of the linker may conform a secondary helical structure. Here we further dissected the structural and functional roles of this linker by systematic alterations of its length. In contrast to voltage-gated K + channels, complete deletion of the S3-S4 linker (Δ229-237) did not produce functional channels. Similarly, the deletions Δ229-234, Δ232-234, and Δ232-237 also abolished normal current activity. Interestingly, Δ229-231, Δ233-237, Δ234-237, Δ235-237, Δ229-231/Δ233-237, Δ229-231/Δ234-237, and Δ229-231/Δ235-237 all yielded robust hyperpolarization-activated inward currents, indicating that loss-of-function caused by deletion could be rescued by keeping the single functionally important residue Met 232 alone. Whereas shortening the linker by deletion generally shifted steady-state activation in the depolarizing direction (e.g. ΔV 1/2 of Δ229-231, Δ233-237, Δ235-237 >+10 mV relative to wild type), linker prolongation by duplicating the entire linker (Dup229-237) or by glutamine insertion (InsQ233Q, InsQQ233QQ and InsQQQ233QQQ, or Ins237QQQ) produced length-dependent progressive hyperpolarizing activation shifts (-35 mV < ΔV 1/2 < -4 mV). Based on these results, we conclude that only Met 232 is prerequisite for channels to function, but the length and other constituents of the S3-S4 linker shape the ultimate activation phenotype. Our results also highlight several evolutionary similarities and differences between HCN and voltage-gated K + channels. Manipulations of the S3-S4 linker length may provide a flexible approach to customize HCN gating for engineering electrically active cells (such as stem cell-derived neuronal and cardiac pacemakers) for gene- and cell-based therapies.link_to_subscribed_fulltex

An evaluation of the factors affecting the quality of highway runoff in the Austin, Texas area

Center for Research in Water Resource

Texas Business Review, July 1974

The Business Situation in Texas; The Effect of Crude-Oil Production on the Economy of Texas; Texas Construction: Housing for the Elderly in Texas, Part 2. Retirement LifestylesBureau of Business Researc

Texas Business Review, January 1974

The Business Situation in Texas; The Input-Output Model for the State of Texas; The Bureau of Business Research, 1926-1974; Texas Construction: Budget MotelsBureau of Business Researc