Biomedical subjects

P Gorostiza

Publications and source records attributed to P Gorostiza.

11 recordsLinked to original sources

PubMed2006

Water exclusion at the nanometer scale provides long-term passivation of silicon (111) grafted with alkyl monolayers.

This work is a quantitative study of the conditions required for a long-term passivation of the interface silicon-alkyl monolayers prepared by thermal hydrosilyation of neat 1-alkenes on well-defined H-Si(111) surfaces. We present electrochemical capacitance measurements (C-U) in combination with ex situ atomic force microscopy (AFM) observations and X-ray photoelectron spectroscopy (XPS) measurements. Capacitance measurements as a function of the reaction time and XPS data reveal close correlations between the chemical composition at the interface and its electronic properties. A very low density of states is found if suboxide formation is carefully prevented. The monitoring of C-U plots and AFM imaging upon exposure of the sample in diverse conditions indicate that the initial electronic properties and structure of the interface are long-lasting only when the monolayer surface coverage is theta > 0.42. A model demonstrates that this threshold value corresponds to a monolayer with intermolecular channels narrower than approximately 2.82 A, which is equal to the diameter of a water molecule. Water exclusion from the monolayer promotes long-term passivation of the silicon surface against oxidation in air and water as well as perfect corrosion inhibition in 20% NH(4)F. We provide two criteria to assess when a sample is optimized: The first one is an effective dielectric constant <2.5, and the second one is a very characteristic energy diagram at open circuit potential.

Alkenes↗

PubMed2002

Sequential atomic force microscopy imaging of a spontaneous nanoencapsulation process.

Since hydrophilic matrices were proposed for controlled drug delivery, many polymeric excipients have been studied in order to make drug release fit the desired profiles. It has been pointed out that lambda-carrageenan, a sulphated polymer from algae, can suitably control the release rate of basic drugs from hydrophilic matrices with no need for complex technological processes. In this work, we propose a method to monitor morphologically the interaction between lambda-carrageenan and dexchlorpheniramine maleate (D-CPM), in order to find out how the release profiles can be so easily controlled. To this end, solutions of both polymer and drug were prepared at very low concentration. Solutions were mixed and samples were taken every hour over a period of 20 h. The characterization technique employed, atomic force microscopy (AFM), provides a high resolution, allowing to show the three-dimensional morphology of the samples within the nanometric scale. The results demonstrate that lambda-carrageenan is able to nanoencapsulate spontaneously D-CPM molecules, which offers the possibility to easily control the release rate of the drug. This work has moreover demonstrated the suitability of AFM for the specific case of the on-time monitoring of interaction processes that happen in pharmaceutical systems.

Carrageenan↗

PubMed2002

Nanoindentation: Toward the sensing of atomic interactions.

The mechanical properties of surfaces of layered materials (highly oriented pyrolytic graphite, InSe, and GaSe) and single-crystal ionic materials (NaCl, KBr, and KCl) have been investigated at the nanometer scale by using nanoindentations produced with an atomic force microscope with ultrasharp tips. Special attention has been devoted to the elastic response of the materials before the onset of plastic yield. A new model based on an equivalent spring constant that takes into account the changes in in-plane interactions on nanoindentation is proposed. The results of this model are well correlated with those obtained by using the Debye model of solid vibrations.

Journal Article↗

PubMed2001

Self-assembly of the amphipathic helix (VHLPPP)8. A mechanism for zein protein body formation.

gamma-Zein, a maize storage protein with an N-terminal proline-rich repetitive domain (gamma-ZNPRD), is located at the periphery of protein bodies. This domain appears to be indispensable for the aggregation of the protein on the surface of the organelle. The peptide (VHLPPP)8, spanning the gamma-ZNPRD, adopts a polyproline II (PPII) conformation that gives an amphipathic helix different from the alpha-helix. We used atomic force microscopy to study the surface organisation of the octamer, and transmission electron microscopy to visualise aggregates of the peptide in aqueous solution. We consider two self-assembly patterns that take account of the observed features. The micellar one fits best with the experimental results presented. Moreover, we found that this peptide has properties associated with surfactants, and form micelles in solution. This spontaneous amphipathic arrangement of the gamma-ZNPRD suggests a mechanism of gamma-zein deposition inside maize protein bodies.

Amino Acid Sequence↗

PubMed1995

Effects of alpha adrenergic stimulation on time independent potassium current of isolated ventricular myocytes.

The role of alpha adrenergic receptor stimulation on ventricular electrical activity is controversial. The aim of the present paper was to study a wide range of concentrations of alpha adrenergic agonists on the electrical properties of guinea pig's heart isolated ventricular myocytes. The experiments were performed according to the single electrode voltage clamp technique. Phenylephrine and epinephrine (in the presence of propranolol) were used at concentrations from 1 x 10(-9) to 10(-5) M. It was observed that both agonists induce an increase in the time independent inward rectifying potassium current (IK1), that could explain the shortening of the action potential. All the observed effects were dose-dependent and disappeared during washout. These results could explain, at least partially, some of the electrical changes observed during ischemia.

Action Potentials↗

PubMed1994

Different mechanism for insulin induced and contraction induced increases in skeletal muscle glucose uptake.

Glucose facilitated diffusion into cells depends on concentration gradients between intracellular and extracellular spaces and can be modified by several factors such as insulin and contractions. Calmodulin participates in the insulin induced recruitment of vesicles containing glucose transporter molecules and its inhibition by trifluoperazine blocks insulin increases in glucose uptake. In the present study we tested if calmodulin inhibition with trifluoperazine blocks hindlimb muscle glucose uptake increase induced by contractions. Trifluoperazine does not inhibit exercise induced increases in glucose uptake; therefore, the mechanisms by which insulin and functional activity increase glucose uptake are different.

Animals↗

PubMed1994

Regulation by glucose availability of tension development and electrical activity in fetal and neonatal rat hearts.

The aim of the present article was to study if changes in glucose availability modify the functional activity of the glucose-dependent developing heart. Our data indicate that a decrease in glucose availability increases tension development and action potential duration at early fetal stages. This fact could probably be explained by the enhancement of Ca2+ movements that regulate the number and turnover rate of membrane glucose transporters in muscle cells. The sensitivity to glucose availability decreases postnatally as the heart becomes fatty acid-dependent.

Action Potentials↗

PubMed1993

Trifluoperazine inhibition of insulin-induced increase in skeletal muscle glucose uptake.

The ability of trifluoperazine, a calmodulin blocker, to prevent increases in skeletal muscle glucose uptake induced by insulin was tested. Insulin significantly increased glucose uptake by the rat hindlimb and trifluoperazine (10(-6) M) completely inhibited this increase. We conclude that calmodulin is a factor involved in the regulation of insulin-mediated glucose transport in muscle cells.

Animals↗

PubMedDate not supplied

[Usefulness of electrophysiologic studies. Report of 224 cases].

Two hundred and twenty four electrophysiologic studies were performed in 194 patients during a two-year period. One hundred and six (54.6%) had tachyarrhythmias: 21 had atrial tachycardia, 28 had the Wolff-Parkinson-White syndrome. Of 51 patients with a normal electrocardiogram a concealed left Kent bundle was observed in 21 cases and only one concealed right Kent bundle; functional James fibers were seen in 7 patients and Mahaim fibers in two. In 15 patients A-V nodal reentry was diagnosed and functional ectopy was observed in 5 patients. The sick-sinus-syndrome was seen in 24 patients and atrial arrest in three. Thirty patients underwent a second electrophysiologic study to evaluate proper antiarrhythmic therapy. Atrioventricular conduction was evaluated in 52 patients. A "suprahisian" delay was found in 34%, troncular lesions were diagnosed in 31%, a distal delay in 25% and mixed conduction disturbances in 10%. We conclude that electrophysiologic studies are a useful procedure to: 1) establish the etiologic diagnosis of tachyarrhythmias; 2) evaluate their potential danger; 3) objectively evaluate antiarrythmic therapy; 4) establish the need for surgical treatment; 5) give the topographic diagnosis and severity of A-V conduction disturbances and 6) indicate the need for definitive pacemaker implant.

Arrhythmias, Cardiac↗

PubMedDate not supplied

[Effects of adenosine on automaticity and post-potential oscillations in Purkinje fibers of mammals].

The aim of the present paper was to study the effects of adenosine (ADO) on automaticity and after potential oscillations on canine cardiac Purkinje fibers. ADO concentrations from 10(-8) to 10(-5) M were used. The intracellular electrical activity was recorded with conventional microelectrodes. ADO increased during the first two minutes the basic cycle length (BLC) with concentrations higher than 10(-8) M, to a value 50% above control, later there is a progression to a steady state. The dose-response curve in the steady state is sigmoidal and resembles those of receptor occupation. The slopes of pacemaker potentials have a tendency to decrease along with the increase in BLC length. After potential oscillations decrease with 10(-8) M of ADO but not with larger concentrations. There results supports the hypothesis that ADO produces an increase in the time independent potassium current similar to the one described for atrial and ventricular myocytes. This effect probably depends on specific receptor stimulation. The biphasic time course suggests the existence of subtypes of A1 receptor with different dissociation constants and affinities but with similar actions. The idea that the ADO effects depend mainly on the potassium currents and not on I(f) is supported by the absence of a dose-dependent effects in the oscillatory after potentials.

Adenosine↗

PubMedDate not supplied

[Mathematics and the heart].

Mathematical modeling in biomedical sciences is particularly difficult because of the great amount of variables that the biological phenomena imply, the difficulty in observation and experimentation, and the scarceness of mathematical methods suitable for incorporating all of these variables. Even so, many mathematical models can be found in biology which include reduccionist, structural or integrative approaches. Theoretical models in biology are designed upon clearly defined purposes and may extent from the molecular level to the intact organism. For a model to be useful, its variables, levels and links must be very explicit. Observable and measurable aspects of the heart allow a modeling approach of this organ, in normal or in pathological conditions. A few examples are mentioned. Mathematical modeling of the heart may help orient experimental research, join existing data and theories and it may also be of assistance as therapeutic guidance.

Humans↗