Biomedical subjects

A Hafezi

Publications and source records attributed to A Hafezi.

8 recordsLinked to original sources

PubMed1998

Subcellular localization and cytotoxic activity of the GroEL-like protein isolated from Actinobacillus actinomycetemcomitans.

The subcellular locations, ultrastructure, and cytotoxic activity of the GroEL-like protein from Actinobacillus actinomycetemcomitans were investigated. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) clearly indicated that synthesis of the GroEL-like protein is substantially increased after a thermal shock. Analysis of the purified native GroEL-like protein by transmission electron microscopy revealed the typical 14-mer cylindrical molecule, which had a diameter of about 12 nm. A. actinomycetemcomitans cells grown at 35 degreesC and heat shocked at 43 degreesC were fractionated, and fractions were separated by SDS-PAGE and analyzed by Western immunoblotting using antibodies to GroEL- and DnaK-like proteins. The GroEL-like protein was found in both the soluble and membrane fractions, whereas the DnaK-like protein was mostly found in the cytoplasm. An increase in specific proteins, including the GroEL- and DnaK-like proteins, was found in heat-shocked cells. The subcellular localization of the GroEL-like protein was examined by immunoelectron microscopy of whole cells. More GroEL-like protein was detected in stressed cells than in unstressed cells, and most of it was found not directly associated with outer membranes but rather in extracellular material. The native GroEL-like protein was assessed for cytotoxic activities. The GroEL-like protein increased the proliferation of periodontal ligament epithelial cells at concentrations between 0.4 and 1.0 microgram/ml. The number of cells in the culture decreased significantly at higher concentrations. A cell viability assay using HaCaT epithelial cells indicated that the GroEL-like protein was strongly toxic for the cells. These studies suggest the extracellular nature of the GroEL-like protein and its putative role in disease initiation.

Aggregatibacter actinomycetemcomitans↗

PubMed1992

Trunk muscle cocontraction: the effects of moment direction and moment magnitude.

This study investigated the cocontraction of eight trunk muscles during the application of asymmetric loads to the torso. External moments of 10, 20, 30, 40, and 50 Nm were applied to the torso via a harness system. The direction of the applied moment was varied by 30 degrees increments to the subjects' right side between the sagittally symmetric orientations front and rear. Electromyographic (EMG) data from the left and right latissimus dorsi, erector spinae, external oblique, and rectus abdominus were collected from 10 subjects. The normalized EMG data were tested using multivariate and univariate analyses of variance procedures. These analyses showed significant interactions between the moment magnitude and the moment direction for seven of the eight muscles. Most of the interactions could be characterized as due to changes in muscle recruitment with changes in the direction of the external moment. Analysis of the relative activation levels, which were computed for each combination of moment magnitude and direction, indicated large changes in muscle recruitment due to asymmetry, but only small adjustments in the relative activation levels due to increased moment magnitude.

Adult↗

PubMed1992

Coactivation of the trunk muscles during asymmetric loading of the torso.

Materials handling tasks in industry are rarely performed in the midsagittal plane. Often these tasks, labeled nonsagittally symmetric or asymmetric lifting tasks, can be expected to lead to an unequal distribution of forces between the left and right sides of the body. Because of the large number of muscles capable of resisting loads in the torso, researchers are forced to make simplifications when using biomechanical models to estimate mechanical loading of the spine during such tasks. Simplifications and assumptions regarding the coactivation of antagonistic muscles are frequently used because sufficient experimental data do not exist. The present study was designed to quantify coactivation of the trunk musculature in response to applied asymmetric loads. This load was varied in direction from an anterior midsagittal plane orientation to a posterior midsagittal plane orientation in 15-deg increments. The results showed little coactivation when the applied load directions were anterior and within 45 deg of the midsagittal orientation. When load directions were greater than 45 deg, coactivation was quantifiable in ipsilateral and posterior muscle groups.

Electromyography↗

PubMed1987

Alpha 2 adrenergic agonists stimulate Na+-H+ antiport activity in the rabbit renal proximal tubule.

The role of adrenergic agents in augmenting proximal tubular salt and water flux, was studied in a preparation of freshly isolated rabbit renal proximal tubular cells in suspension. Norepinephrine (NE, 10(-5) M) increased sodium influx (JNa) 60 +/- 5% above control value. The alpha adrenergic antagonist, phentolamine (10(-5) M), inhibited the NE-induced enhanced JNa by 90 +/- 2%, while the beta adrenergic antagonist, propranolol, had a minimal inhibitory effect (10 +/- 2%). The alpha adrenergic subtype was further defined. Yohimbine (10(-5) M), an alpha2 adrenergic antagonist but not prazosin (10(-5) M), an alpha1 adrenergic antagonist completely blocked the NE induced increase in JNa. Clonidine, a partial alpha2 adrenergic agonist, increased JNa by 58 +/- 2% comparable to that observed with NE (10(-5) M). Yohimbine, but not prazosin, inhibited the clonidine-induced increase in JNa, confirming that alpha2 adrenergic receptors were involved. Additional alpha2 adrenergic agents, notably p-amino clonidine and alpha-methyl-norepinephrine, imparted a similar increase in JNa. The clonidine-induced increase in JNa could be completely blocked by the amiloride analogue, ethylisopropyl amiloride (EIPA, 10(-5) M). The transport pathway blocked by EIPA was partially inhibited by Li and cis H+, but stimulated by trans H+, consistent with Na+-H+ antiport. Radioligand binding studies using [3H]prazosin (alpha1 adrenergic antagonist) and [3H]rauwolscine (alpha2 adrenergic antagonist) were performed to complement the flux studies. Binding of [3H]prazosin to the cells was negligible. In contrast, [3H]rauwolscine showed saturable binding to a single class of sites, with Bmax 1678 +/- 143 binding sites/cell and KD 5.4 +/- 1.4 nM. In summary, in the isolated rabbit renal proximal tubular cell preparation, alpha2 adrenergic receptors are the predominant expression of alpha adreno-receptors, and in the absence of organic Na+-cotransported solutes, alpha2 adrenergic agonists enhance 22Na influx into the cell by stimulating the brush border membrane Na+-H+ exchange pathway.

Adrenergic alpha-Agonists↗

PubMed1986

Characteristics of the Na+-H+ antiporter in the intact renal proximal tubular cell.

The characteristics of the proximal tubular Na+-H+ antiporter were determined in isolated proximal tubular cells to ascertain whether the features of this transport system in intact cells are comparable with those previously described for isolated brush-border membrane vesicles. A method is described for the rapid isolation of a purified preparation of cells that demonstrate morphological and functional characteristics of the renal proximal tubule. The cells maintain their polarity while in suspension, and adenylate cyclase activity is enhanced by parathyroid hormone but not by arginine vasopressin. The cells display gluconeogenic function and Na+-dependent alpha-methyl-D-glucose and organic phosphate cotransport, processes that confirm their proximal tubule origin. O2 consumption rates and cytosolic adenosine triphosphate levels indicate functional integrity. Na+-H+ antiport activity was defined in these cells by measuring amiloride-sensitive Na+ uptake. At intracellular pH = 6.4 vs. extracellular pH = 7.4, KtNa was 10.1 +/- 2.8 mM, and maximal sodium flux was 0.89 +/- 0.13 nmol X 10(6) cells-1 X K0.5 for amiloride and ethyl-isopropyl amiloride, measured at an external Na+ concentration of 1 mM, was observed at 2.5 X 10(-5) M and 2.9 X 10(-6) M, respectively. The external and internal loci of the exchanger displayed asymmetric affinity for the hydrogen ion: the apparent pK for the external site was 7.20-7.26 vs. less than 6.5 for the internal site. The internal site demonstrated features of positive cooperativity. In summary, the Na+-H+ antiporter present in the luminal membrane of the renal proximal tubule has been characterized in the intact cell and displays functional and kinetic parameters closely resembling those described in isolated brush-border membrane vesicles.

Adenylyl Cyclases↗

PubMed1985

pH gradient-dependent increased Na+-H+ antiport capacity of the rabbit remnant kidney.

The adaptative response of the renal proximal tubule to a reduction of renal mass was studied in brush border membrane vesicles prepared from the solitary remnant kidney (RK) of subtotally nephrectomized rabbits. The in vivo acid-base status of RK and sham-operated controls (SK) was similar. In the absence of organic solutes, Na+ flux across the membrane demonstrated features of Na+-H+ antiport, i.e., stimulation by a transmembrane pH gradient and inhibition by amiloride. Kinetic parameters for Na+-H+ antiport were derived with different experimental protocols. In the presence of an opposing H+ gradient and over a limited range of Na+ concentration, JNamax was enhanced 65% in RK vesicles compared with SK vesicles and KtNa was unchanged. The enhanced JNamax was not apparent under H+ equilibrium conditions, Comparable values for JNamax and KtNa were obtained by studying RK vesicles at external Na+ concentrations of 0-200 mM and resolving uptake into a substrate component, representing Na+-H+ antiport, and a nonsaturable diffusive component. The apparent Na+ permeability (P'Na) of RK vesicles was identical to the P'Na of normal kidney vesicles, under both H+ gradient and H+ equilibrium conditions. H+ permeability, measured with acridine orange, was also the same in RK and SK vesicles. These studies demonstrate that in the remnant kidney model of chronic renal insufficiency there is an increase in the JNamax of the Na+-H+ antiporter in the luminal membrane of the proximal tubule that is revealed only under transmembrane H+ gradient conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗

PubMed1984

Mechanisms of Na+ uptake into renal brush border membrane vesicles.

Brush border membrane vesicles were used to investigate the pathways for Na+ uptake across the apical membrane of the renal proximal tubular cell. The kinetics of uptake in the absence of organic solutes were consistent with parallel saturable and nonsaturable pathways. At pH equilibrium (pHin = pHout = 7.5), the Jmax and Kt for saturable uptake were 41 +/- 15 (+/- SE) nmol X mg-1 X min-1 and 33 +/- 9, respectively, and the apparent permeability coefficient, P'Na, was 0.27 +/- 0.02 microliters X mg-1 X min-1. As the equilibrium pH was varied between 6.0 and 8.0, no consistent trend for Kt or P'Na was observed; Jmax varied up to twofold. In contrast, in the presence of an outward H+ gradient (pHin = 6.0 vs. pHout = 7.5), the Kt decreased by an order of magnitude, with little change in Jmax. At low sodium concentrations (1 mM) external Li+ and NH+4, and to a lesser extent K+, Rb+, and Cs+, inhibited Na+ uptake. Amiloride (10(-3) M) inhibited 1 mM Na+ uptake by 80% even in the absence of a H+ gradient. Uptake also varied with the anion composition at high sodium concentrations (100 mM), as predicted from the anion permeabilities. Sodium uptake was more sensitive to variations in membrane potential at high sodium concentrations than at low concentrations. On the basis of these experiments we suggest that the saturable Na+ uptake occurs via an electroneutral Na+-H+ antiporter and that the diffusive flux occurs through a conductive pathway.

Amiloride↗

PubMedDate not supplied

Trunk muscle geometry and centroid location when twisting.

The trunk muscles of the lumbar region were studied using magnetic resonance imaging (MRI) in five male volunteers placed in neutral and in two twisted postures. Using a CAD digitizing system, the positions of trunk muscle centroids and the cross-sectional areas of these muscles were measured from the transverse scans at 1 cm intervals from L2 to S1. Muscle lines of action were created by connecting the muscle centroids from the successive sections. Changes in cross-sectional areas and displacements of centroids in a three-dimensional coordinate system and the local two-dimensional coordinate system were estimated at each disc level. In the three-dimensional coordinate system, all muscle centroids were displaced when twisting. Thus, the locations and orientations of all muscle lines of action changed. In the local two-dimensional coordinate system, only the muscle centroids of four abdominal muscles were displaced. Most of these displacements occurred in the first 25 degrees of twisting. Higher up in the lumbar spine, the displacement was greater. The changes in moment arms were sometimes as great as twofold. Only the abdominal oblique muscles (AOM) changed their cross-sectional area significantly; the area of the right AOM ipsilateral to the side of twisting increased, while that of the left AOM was decreased.

Abdominal Muscles↗