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F Valenzuela

Publications and source records attributed to F Valenzuela.

At least 19 recordsLinked to original sources
PubMed2002

Study of the influence of the pH media dissolution, degree of polymerization, and degree of swelling of the polymers on the mechanism of release of diltiazem from matrices based on mixtures of chitosan/alginate.

The dissolution profiles of formulations based on mixtures of chitosan/alginate depend on the pH. It is possible to distinguish two processes: (a) a fast kinetic drug release up to 180 min, where the pH value changes from 1.17 to 2.21 and the drug released is controlled by the degree of polymerization and the quantity of chitosan in the formulation; (b) a low kinetic drug release between 210 and 480 min, where the pH value changes from 5.52 to 8.72 and the drug release from the matrix is controlled by the interpolymeric complex. In all formulations the order of release, according to Peppas's model in the range of fast kinetic drug release, was between 0.5 and 1.0. The mechanism of release was non-fickian diffusion, which corresponds to a coupling mechanism of diffusion and relaxation of the polymer.

Alginates↗
PubMed2000

[Use of amphotericin B in lipid emulsions: does it prevent its toxicity in critically ill patients?].

BACKGROUND: Amphotericin B is efficacious for the treatment of systemic candidiasis, however it has potentially serious toxic effects. Administration as lipid emulsions has been advocated to decrease its toxicity. AIM: To compare the safety and tolerance of amphotericin B administered as lipid emulsion or dissolved in dextrose in water. PATIENTS AND METHODS: Forty five patients with confirmed or highly suspected systemic candidiasis were studied. Between January 1996 and June 1997 amphotericin B was administered in dextrose in water to 17 patients (group 1). Between July 1997 and December 1998, the drug was delivered in lipid emulsions (Intralipid, group 2). Clinical and laboratory parameters (serum creatinine, urea nitrogen and potassium), were assessed daily. RESULTS: Both treatment groups were clinically comparable and had the same survival. Accumulative amphotericin B dose administered was 343.2 +/- 197 and 414.6 +/- 518 mg respectively. Hypokalemia was more frequent in group 2 (52 and 25% respectively, p < 0.05). There were no differences in the outcome of renal function or other adverse reactions. CONCLUSIONS: Administration of amphotericin B as lipid emulsions did not reduce its toxicity in critical patients (Rev Méd Chile 2000; 128: 1101-07).

APACHE↗
PubMed1998

Involvement of different Ca2+ pools during the canine bronchial sustained contraction in Ca2+-free medium: lack of effect of PKC inhibition.

We evaluated the role of protein kinase C (PKC) in the sustained bronchial contraction (SBC) induced by carbachol (Cch) or histamine in a Ca2+-free medium and the possibility that each agonist uses a different Ca2+ store for this response. We studied third-order bronchi and airway smooth muscle (ASM) from first-order bronchi dissected free of cartilage and epithelium. Bronchial and ASM responsiveness to Cch or histamine were evaluated in Krebs solution (2.5 mM Ca2+) and in Ca2+-free medium. Cch and histamine induced an SBC in bronchial tissues in Ca2+-free medium. In ASM each agonist produced a transient contraction, but the response to histamine was much smaller. Cch induced a concentration-dependent accumulation of inositol phosphates (IPs) in both bronchi and ASM; however, histamine did not induce significant accumulation of IPs. Repeated exposure to histamine in bronchial rings abolished contractile responses in Ca2+-free media, but Cch added afterwards still produced a sustained contraction. This response was blocked when bronchial tissues were preincubated with 10 microM cyclopiazonic acid (CPA). Brief incubation of these preparations with a high EGTA concentration (1 mM) abolished the histamine-induced SBC. The SBC induced by Cch or histamine in Ca2+-free medium was not affected by the preincubation of the tissues with calphostin C, chelerythrine or staurosporine. We concluded that Cch mobilizes Ca2+ from two different sources during the SBC in Ca2+-free medium: from a CPA-sensitive one from sarcoplasmic reticulum (SR) and from a putative extracellular membrane Ca2+ pool sensitive to 1 mM EGTA, and neither process involved PKC activation. Histamine appeared to utilize the extracellular membrane pool only.

Animals↗
PubMed1997

Estrogenic effects of p-hydroxybenzoic acid in CD1 mice.

Xenobiotic estrogens in the environment or diet have received much attention as a possible source of certain hormonal disease states in human and wildlife. Therefore, the detection of estrogenic activity of any substance, especially those related to the food industry, is important. The estrogenic activity of p-hydroxybenzoic acid (PHBA), a compound related to a commonly used group of preservatives in food, cosmetic, and pharmaceutical preparations, was evaluated with immature and adult ovariectomized female mice (CD1) using two well-known bioassays. Subcutaneous administrations (s.c.) of different doses of PHBA were compared with estradiol (E2), and their effects on vaginal cornification and uterotrophic activities were evaluated. Different groups of animals were treated s.c. daily for 3 days with vehicle (corn oil, 0.3 ml/100 g), E2 (1 microgram/100 g), and PHBA (0.5, 5, 50, and 500 micrograms/100 g). Four days after treatment, PHBA produced a dose-dependent response on vaginal cornification and uterotrophic activity in both immature and adult ovariectomized mice. The relative uterotrophic potency of PHBA (500 micrograms/100 g) to E2 (1 microgram/100 g) was 0.0011 in immature mice and 0.0018 in ovariectomized animals.

Animals↗
PubMed1997

A JAVA-based multimedia tool for clinical practice guidelines.

We have developed a specific language for the representation of Clinical Practice Guidelines (CPGs) and Windows C++ and platform independent JAVA applications for multimedia presentation and edition of electronically stored CPGs. This approach facilitates translation of guidelines and protocols from paper to computer-based flowchart representations. Users can navigate through the algorithm with a friendly user interface and access related multimedia information within the context of each clinical problem. CPGs can be stored in a computer server and distributed over the World Wide Web, facilitating dissemination, local adaptation, and use as a reference element in medical care. We have chosen the Agency for Health Care and Policy Research's heart failure guideline to demonstrate the capabilities of our tool.

Computer Communication Networks↗
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↗
PubMed1991

Role of membrane potential in Ba2+ induced automaticity in guinea pig cardiac myocytes.

STUDY OBJECTIVE: The aim was to study in isolated myocardial cells the role of membrane potential in barium induced spontaneous activity and the ionic mechanism of the underlying pacemaker current. DESIGN: The membrane potential and resistance of single myocytes were studied at different voltage levels by means of current and voltage clamp steps in the absence and presence of barium (Ba). EXPERIMENTAL MATERIAL: The membrane potentials and currents of single guinea pig ventricular myocytes were recorded by means of an intracellular microelectrode through which current could also be passed. MEASUREMENTS AND MAIN RESULTS: In the presence of Ba (0.1-0.2 mM), stepwise depolarisations induced a transient overshoot and initiated action potentials followed by an undershoot, diastolic depolarisation and spontaneous discharge. During progressive depolarisations, membrane resistance (Rm) increased, decreased transiently at the end of the action potential, and reincreased during diastole. Stepwise repolarisations had opposite effects. Hyperpolarisations reversed diastolic depolarisation and could unmask oscillatory potentials (Vos). Voltage clamp steps to +20 mV were followed by outward tail currents during which Rm increased. Larger or longer depolarisations were followed by larger outward tail currents at resting potential level. The outward tail current reversed at potentials negative to EK. CONCLUSIONS: In the presence of Ba, applied depolarisation facilitates the induction of spontaneous activity through an interplay between voltage dependent and time dependent Ba block and unblock of gK1, voltage dependent increase in Rm, increased potassium driving force, and negative shift in the slow inward current threshold and sometimes Vos. The pacemaker potential underlying spontaneous activity is due to the slow re-establishment of Ba block of IK1 during diastole.

Action Potentials↗
PubMed1989

On the mechanism of barium induced diastolic depolarisation in isolated ventricular myocytes.

Barium can induce spontaneous activity in cardiac non-pacemaker cells. The mechanism of barium induced diastolic depolarisation was studied in isolated ventricular myocytes, using a microelectrode technique. Barium (0.05-0.2 mmol.litre-1) decreased resting potential and caused the membrane potential at the end of the action potential to undershoot the diminished resting value temporarily, thereby inducing diastolic depolarisation. Resting membrane resistance was increased by Ba but at the end of phase 3 repolarisation the resistance temporarily decreased below its steady state diastolic value. In presence of Ba, hyperpolarisation abolished or reversed diastolic depolarisation. At the end of phase 3 repolarisation, membrane resistance was decreased, whether diastolic depolarisation was present, absent or reversed. A high [K]o (15.4 mmol.litre-1) decreased Ba effects on action potential, membrane resistance and diastolic depolarisation. Caesium decreased the Ba induced diastolic depolarisation and the associated increase in membrane resistance, but had little effect on spontaneous activity at depolarised levels. Barium induced an oscillatory potential, with increased membrane resistance. Noradrenaline plus low [Ba]o, and high [Ba]o alone (1-5 mmol.litre-1), can induce spontaneous activity. Thus, in myocardial cells barium induces diastolic depolarisation at polarised levels by a voltage and time dependent block of potassium conductance, which is modulated by action potential voltage changes. However, as [Ba]o is increased, spontaneous activity at a depolarised level may be related to the decay of potassium currents and to oscillatory potentials.

Action Potentials↗
PubMed1985

The two components in the shortening of unloaded ventricular myocytes: their voltage dependence.

In isolated myocytes from mammalian ventricles a fast and a slow component in the contractile response to depolarizing voltage clamp steps were identified. The potential dependence of the slow component was identical to the activation curve of iCa. The fast component, however, remained at its maximal amplitude at potentials positive to +10 mV (up to +100 mV), in which potential range iCa declined and eventually disappeared. The results suggest that the slow component may be activated by Ca++ entering through sarcolemmal Ca channels, whereas the fast component depends on Ca release from intracellular sites and may depend on both Cai and voltage.

Animals↗
PubMed1985

Overdrive excitation and cellular calcium load in canine cardiac Purkinje fibers.

The induction of spontaneous activity by drive ("overdrive excitation") was studied by means of a microelectrode technique in canine cardiac Purkinje fibers exposed to an enhanced calcium load. The following results were obtained: 1) in quiescent fibers, a single action potential is followed by a prolonged transitory depolarization ("slow afterdepolarization") that may initiate a slow spontaneous rhythm; 2) during short drives, the maximum diastolic potential (Emax) gradually decreases and diastolic depolarization becomes steeper due to a superimposed oscillatory potential of progressively greater amplitude; 3) after the drive, the oscillatory potential either initiates a fast repetitive activity or is followed by a slow repolarization to the original resting level; 4) the cessation of induced activity is associated with an increase in Emax; 5) during longer and faster drives, Emax increases and the oscillatory potential becomes smaller, peaks sooner and may fail to excite; 6) repetitive activity may also be induced at a depolarized level. We conclude that overdrive excitation involves an increased cellular calcium, can occur at normal or depolarized levels, and is induced by an oscillatory potential superimposed on a slow afterdepolarization. It is most easily initiated by a short and fast drive because at that time the oscillatory potential and slow afterdepolarization are optimally combined to induce activity.

Animals↗