PubMed Health⌕ Search

Biomedical subjects

M A Valverde

Publications and source records attributed to M A Valverde.

At least 19 recordsLinked to original sources
PubMed1999

Acute activation of Maxi-K channels (hSlo) by estradiol binding to the beta subunit.

Maxi-K channels consist of a pore-forming alpha subunit and a regulatory beta subunit, which confers the channel with a higher Ca(2+) sensitivity. Estradiol bound to the beta subunit and activated the Maxi-K channel (hSlo) only when both alpha and beta subunits were present. This activation was independent of the generation of intracellular signals and could be triggered by estradiol conjugated to a membrane-impenetrable carrier protein. This study documents the direct interaction of a hormone with a voltage-gated channel subunit and provides the molecular mechanism for the modulation of vascular smooth muscle Maxi-K channels by estrogens.

Animals↗
PubMed1999

ClC channels: leaving the dark ages on the verge of a new millennium.

The field of molecular physiology of ClC chloride channels has witnessed a tremendous surge in knowledge over the past few years; however, fundamental issues such as the stoichiometry of ClC channels and the identification of pore-lining sequences have only recently begun to be addressed. New studies have also provided important insights into the role of ClC channels in cell volume regulation and their function in intracellular organelles.

Animals↗
PubMed1999

Risk factors for atherosclerosis in students of a private university in São Paulo-Brazil.

OBJECTIVE: To characterize the risk profile for atherosclerosis (AS) in adolescents and young adults of a private university in São Paulo. METHODS: Clinical, nutritional, and laboratory parameters were evaluated in 209 students of both genders aged 17 to 25 years. In addition to determination of the lipid profile, the association of its abnormal values with other risk factors for AS was also investigated. RESULTS: Increased levels of total cholesterol, LDL-C and triglycerides (TG) were observed in 9.1%, 7.6% and 16.3% of the students, respectively, and decreased levels of HDL-C in 8.6% of them. Prevalence of the remaining risk factors analyzed was elevated: sedentary life style (78.9%); high intake of total fat (77.5%); high cholesterol intake (35.9%); smoking, hypertension (15.8%) and obesity (7.2%). There was an association between elevated LDL-C and TG levels and sedentary life style and body mass index. CONCLUSION: The high prevalence of risk factors for AS in young individuals draws attention to the need for adopting preventive plans.

Adolescent↗
PubMed1999

[Changes in lipid profile in obese children and adolescents].

Alterations in plasmatic lipid profile are known to be risk factors for atherosclerotic disease and have been associated with obesity. This research was designed in order to study the incidence of these alterations in obese children and adolescents according to two different reference patterns. Analyses of seric levels of Total Cholesterol (CT) and fractions and of Triglycerides (TG) were done. The sample included 74 obese children and adolescents with average age equal to 11 years and 10 months for boys and 10 years and 9 months for girls and with mean weight/height ratio (W/H) equal to 151 and 149% for boys and for girls, respectively. Plasmatic lipid values obtained were classified according to the American Heart Position Statement Circulation (AHPSC) and to Kwiterovich reference patterns. It was observed that patients with abnormal seric HDL-cholesterol (HDL) levels had a significantly greater (W/H) then the other group. It was also noticed that a greater number of individuals presented abnormal or borderline plasmatic lipid levels (91.9%), specially HDL (93.6%) and TG (67.6%), according to Kwiterovich than AHPSC. Obesity showed to be an important factor in determining lipid profile values and should be included as a variable to indicate screening of these lipoproteins in childhood and adolescence.

Adolescent↗
PubMed1998

Inhibition of voltage-gated cationic channels in rat embryonic hypothalamic neurones and C1300 neuroblastoma cells by triphenylethylene antioestrogens.

The effect of the non-steroidal antioestrogens tamoxifen and toremifene on voltage-gated cationic currents was examined in primary cultures of rat hypothalamic neurones and the C1300 mouse neuroblastoma cell line using the whole-cell patch clamp technique. When applied to the external bathing solution both tamoxifen and toremifene were able to inhibit TTX-sensitive sodium currents with IC50 values of 1-2 microM and delayed rectifier type potassium currents (IC50, 2-3 microM). However, only toremifene showed a significant inhibition of the I(A) current (IC50 3 microM). Inhibition of voltage-gated cationic currents was significantly impaired when tamoxifen was applied in a serum-containing solution. The steroidal antioestrogen ICI 182,780 did not inhibit any of the currents at 10 microM.

Animals↗
PubMed1998

Osmosensitive C1- currents and their relevance to regulatory volume decrease in human intestinal T84 cells: outwardly vs. inwardly rectifying currents.

1. The swelling-activated outwardly rectifying Cl- current (ICl(swell)) recorded in T84 human intestinal cells was completely blocked by 10 microM tamoxifen, while 300 microM Cd2+ had no effect. 2. A ClC-2-like, inwardly rectifying Cl- current was activated after strong hyperpolarization in T84 cells. This current was completely inhibited by 300 microM Cd2+, unaffected by 10 microM tamoxifen, and its magnitude increased slightly in response to cell swelling under hyposmotic conditions. However, the swelling-dependent modulation occurred only after prior activation by hyperpolarizing voltages. 3. T84 cells behaved initially close to perfect osmometers in response to changes in external osmolalities between +20 and -30 %. The cells underwent full regulatory volume decrease (RVD) within 16 min when exposed to 30 or 10 % hyposmotic shocks. 4. Pharmacological tools were used to determine the anionic pathway(s) involved in RVD in T84 cells. Tamoxifen (10 microM), 1,9-dideoxyforskolin (DDFSK; 100 microM) and 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS; 100 microM) blocked RVD while 300 microM Cd2+ had no effect upon RVD following a 30 % hyposmotic shock. The RVD response was similarly unaffected by Cd2+ when cells were exposed to a smaller (10 %) hyposmotic shock. 5. In conclusion, these data show that the anionic pathway primarily activated by cell swelling and relevant to RVD in T84 cells is the tamoxifen-, DDFSK- and DIDS-sensitive ICl(swell) and not the hyperpolarization-activated, Cd2+-sensitive Cl- current associated with the ClC-2 Cl- channel.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1998

Inhibition of ligand-gated cation-selective channels by tamoxifen.

The nonsteroidal antioestrogen tamoxifen has been shown to block a number of voltage-gated cation-selective channels but its effect on ligand-gated cation-selective channels has not been studied. We have investigated the action of tamoxifen and the related derivative toremifene on ligand-gated cationic nicotinic acetylcholine and 5-HT3 receptor channels. Tamoxifen and toremifene both inhibited cationic currents of adult-type human muscle nicotinic acetylcholine receptors expressed in Xenopus oocytes with similar IC50 values of 1.2 +/- 0.03 microM (nH = 0.84 +/- 0.02) and 1.2 +/- 0.1 microM (nH = 1.1 +/- 0.1), respectively. Tamoxifen could also block native 5-HT3 receptors in NG108-15 neuroblastoma/glioma hybrid cells with IC50 = 0.81 +/- 0.15 microM and nH of 1.3 +/- 0.3. The characteristics of block by tamoxifen at the 5-HT3 receptor were voltage- and use-independent. The inhibition of the 5-HT-evoked currents were not overcome by increasing concentrations of 5-HT consistent with a noncompetitive mechanism of block.

Animals↗
PubMed1998

Protein kinase C phosphorylation disengages human and mouse-1a P-glycoproteins from influencing the rate of activation of swelling-activated chloride currents.

1. Whole-cell, swelling-activated Cl- currents, ICl(swell), were characterized in Chinese hamster ovary (CHO) cells and found to exhibit time-dependent inactivation at depolarizing potentials, tamoxifen and dideoxyforskolin sensitivity, and an anion permeability sequence: SCN- > I- > Br- > Cl- > F- > gluconate-. 2. CHO cells permanently transfected with either the human MDR1 or mouse mdr1a cDNAs demonstrated an increased rate of activation of ICl(swell) compared with parental cells or those permanently transfected with the mouse mdr1b cDNA. However, no differences in the magnitude of the currents were observed at steady state. 3. Pretreatment with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) did not affect ICl(swell) in MDR1 or mdr1a permanently transfected CHO cells. In contrast, pretreatment with TPA reduced ICl(swell) in MDR1(G185V)-expressing transfected NIH3T3 fibroblasts. Subsequently, the CHO cell lines were shown to contain significantly reduced levels of protein kinase C (PKC), suggesting that PKC concentrations might be limiting in these cell lines, at least under whole-cell patch clamp conditions. 4. Addition of purified PKC to the pipette solution, followed by a pretreatment with TPA, reduced the rate of ICl(swell) activation in human Pgp- and mouse Pgp1a-expressing CHO cells to the levels observed in parental and mouse Pgp1b-expressing cells. This confirms that PKC is limiting in these cells under whole-cell, patch clamp conditions. Furthermore, these results suggest that PKC-mediated phosphorylation of human Pgp and mouse Pgp1a disengages the influence which these Pgps have on ICl(swell). 5. These studies also demonstrate a functional distinction between the two mouse homologues, Pgp1a and Pgp1b. Although both can function as drug efflux pumps, only Pgp1a can act like human Pgp to influence ICl(swell).

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

Outcomes of obese children and adolescents enrolled in a multidisciplinary health program.

OBJECTIVE: The study was designed to evaluate the impact of a multidisciplinary program on children and adolescents' weight control. DESIGN: Retrospective study regarding changes in relative weight of all patients treated regularly in an out-patient care public service between January 1992 and December 1993. SUBJECTS: 198 children and adolescents (108 girls and 90 boys; mean age: 9.25y; mean body mass index (BMI): 24.26 kg/m2, range 19.1-40.31). MEASUREMENTS: Anthropometric data collected at the visits were obtained until June 30 1994. BMI compared to reference data was used. Dual Photon X-ray Absorptiometry (DEXA) was used for 64 patients, to determine percent body fat. RESULTS: Relative weight at the last visit was significantly lower when compared with initial relative weight for the whole sample. Significantly better outcome of relative weight was obtained when six or more visits occurred for the whole sample, and for girls when the days' interval between visits was shorter than 52 d. Variables such as percent body fat, body shape at the first visit, family obesity pattern, length of obesity and pubertal stage, did not significantly influence the outcome of relative weight for the subjects during the treatment. CONCLUSION: Results obtained indicated that good outcomes can be obtained in a program using nutrition education focused on small modifications of eating habits in order to avoid excess energy intake. The best predictors of weight improvement for children and adolescents participating in the program were the higher frequency of visits and shorter intervals between them.

Adolescent↗
PubMed1998

Environmental estrogenic pollutants induce acute vascular relaxation by inhibiting L-type Ca2+ channels in smooth muscle cells.

There is an ongoing scientific debate concerning the potential threat of environmental estrogenic pollutants to animal and human health (1-5). Pollutants including the detergents 4-octylphenol and p-nonylphenol and chlorinated insecticides have recently been reported to modulate sexual differentiation by interacting with nuclear steroid receptors (6-8). So far, the focus has been on reproductive organs, but sex steroids have far more widespread actions. The lower incidence of cardiovascular disease in women has been attributed to estrogens (9-14), yet no information is available on the vascular actions of environmental estrogenic pollutants. In the present study we have investigated the effects of acute exposure to 17beta-estradiol, the antiestrogen ICI 182,780, and estrogenic pollutants on coronary vascular tone as well as on intracellular Ca2+ levels ([Ca2+]i) and Ca2+ and K+ channel activity in vascular smooth muscle cells. We report here that 4-octylphenol, p-nonylphenol, o.p'-DDT, and the antiestrogen ICI 182,780 inhibit L-type Ca2+ channels in vascular smooth muscle cells and evoke a rapid and endothelium-independent relaxation of the coronary vasculature similar to that induced by 17beta-estradiol. Thus, inhibition of Ca2+ influx via L-type Ca2+ channels in vascular smooth muscle cells may explain the acute, nongenomic vasodilator actions of environmental estrogenic pollutants.

Animals↗
PubMed1996

The multidrug resistance P-glycoprotein modulates cell regulatory volume decrease.

Cell volume is frequently down-regulated by the activation of anion channels. The role of cell swelling-activated chloride channels in cell volume regulation has been studied using the patch-clamp technique and a non-invasive microspectrofluorimetric assay for changes in cell volume. The rate of activation of these chloride channels was shown to limit the rate of regulatory volume decrease (RVD) in response to hyposmotic solutions. Expression of the human MDR1 or mouse mdr1a genes, but not the mouse mdr1b gene, encoding the multidrug resistance P-glycoprotein (P-gp), increased the rate of channel activation and the rate of RVD. In addition, P-gp decreased the magnitude of hyposmotic shock required to activate the channels and to elicit RVD. Tamoxifen selectively inhibited both chloride channel activity and RVD. No effect on potassium channel activity was elicited by expression of P-gp. The data show that, in these cell types, swelling-activated chloride channels have a central role in RVD. Moreover, they clarify the role of P-gp in channel activation and provide direct evidence that P-gp, through its effect on chloride channel activation, enhances the ability of cells to down-regulate their volume.

3T3 Cells↗
PubMed1995

Impaired cell volume regulation in intestinal crypt epithelia of cystic fibrosis mice.

Cystic fibrosis is a disease characterized by abnormalities in the epithelia of the lungs, intestine, salivary and sweat glands, liver, and reproductive systems, often as a result of inadequate hydration of their secretions. The primary defect in cystic fibrosis is the altered activity of a cAMP-activated Cl- channel, the cystic fibrosis transmembrane conductance regulator (CFTR) channel. However, it is not clear how a defect in the CFTR Cl- channel function leads to the observed pathological changes. Although much is known about the structural properties and regulation of the CFTR, little is known of its relationship to cellular functions other than the cAMP-dependent Cl- secretion. Here we report that cell volume regulation after hypotonic challenge is also defective in intestinal crypt epithelial cells isolated from CFTR -/- mutant mice. Moreover, the impairment of the regulatory volume decrease in CFTR -/- crypts appears to be related to the inability of a K+ conductance to provide a pathway for the exit of this cation during the volume adjustments. This provides evidence that the lack of CFTR protein may have additional consequences for the cellular function other than the abnormal cAMP-mediated Cl- secretion.

Animals↗
PubMed1995

Protein kinase C-mediated phosphorylation of the human multidrug resistance P-glycoprotein regulates cell volume-activated chloride channels.

The multidrug resistance P-glycoprotein (P-gp), which transports hydrophobic drugs out of cells, is also associated with volume-activated chloride currents. It is not yet clear whether P-gp is a channel itself, or whether it is a channel regulator. Activation of chloride currents by hypotonicity in cells expressing P-gp was shown to be regulated by protein kinase C (PKC). HeLa cells exhibited volume-activated chloride currents indistinguishable from those obtained in P-gp-expressing cells except that they were insensitive to PKC. HeLa cells did not express detectable P-gp but, following transient transfection with cDNA encoding P-gp, the volume-activated channels acquired PKC regulation. PKC regulation was abolished when serine/threonine residues in the consensus phosphorylation sites of the linker region of P-gp were replaced with alanine. Replacement of these residues with glutamate, in order to mimic the charge of the phosphorylated protein, also mimicked the effects of PKC on channel activation. These data demonstrate that PKC-mediated phosphorylation of P-gp regulates the activity of an endogenous chloride channel and thus indicate that P-gp is a channel regulator.

3T3 Cells↗
PubMed1995

Chloride channels: a state of flux.

Chloride channels play important functions in different aspects of cell physiology including volume regulation, transepithelial ion transport and stabilization of membrane potential. In recent years the molecular identity of the chloride channels defective in cystic fibrosis and myotonia congenita has been elucidated, highlighting the importance of anion-selective channels in cell and tissue function. Concurrently, several proteins have been identified as chloride channels along with proteins that possess channel regulatory behavior. Novel interactions with more potent pharmacological compounds have been reported with different chloride channels. This burgeoning field of interest is reviewed.

Animals↗
PubMed1995

Lens opacification by antioestrogens: tamoxifen vs ICI 182,780.

The antioestrogen, tamoxifen, blocks volume-regulated chloride channels and reduces transparency in bovine lenses maintained in vitro. In contrast to tamoxifen, the steroidal antioestrogen, ICI 182780, did not block volume-regulated chloride currents in three cultured cell lines and required 10 fold higher concentration to induce significant opacification of bovine lenses maintained in vitro. These data suggest that ocular toxic side effects will be minimized by use of the steroidal (ICI 182780) rather than nonsteroidal antioestrogens (tamoxifen).

Animals↗
PubMed1994

Cl- currents of unstimulated T84 intestinal epithelial cells studied by intracellular recording.

The ionic currents spontaneously present in T84 intestinal epithelial cells, a line of colonic carcinoma origin, have been studied using the whole-cell recording mode of the patch-clamp technique and the single-electrode voltage-clamp method. Patch-clamp experiments showed that nonstimulated T84 cells already possess large currents but that these tend to disappear during the course of the experiments, presumably through the dialysis of some essential cytoplasmic component against the micropipette solution. The main charge carrier in these experiments appears to be Cl- as judged from ion replacement. Microelectrode impalement of T84 cells gave a membrane potential of around -30 mV, similar to the equilibrium potential for Cl- estimated from previously published values for intracellular Cl- concentration. Voltage-clamp experiments with a single microelectrode revealed three kinetically distinguishable current patterns; currents decaying during hyperpolarizing voltage pulses, currents slowly activating during hyperpolarizing pulses and time-independent currents. The appearance of these distinct kinetic patterns was not predictable from cell to cell, and was not dependent on extracellular Ca2+. Ionic replacement experiments suggest that the charge carrier was always Cl-, regardless of the kinetic pattern observed. No K+ currents appear to be present in the non-stimulated T84 cells. Exposure of T84 cells to the muscarinic agonist carbachol induced a shift in the membrane potential towards more negative values, consistent with an activation of a K+ conductance. Thus, we suggest that the resting membrane potential in T84 cells is determined by the distribution of Cl-. This might imply that activation of K+ conductance could by itself support secretion by T84 monolayers through tonically active Cl- channels.

Carbachol↗