The concentration dependence of the depolarization of yeast by monovalent cations.

Monovalent cations decrease the initial rate of uptake of the membrane potential probe 2-(dimethylaminostyryl)-1-ethyl-pyridinium (DMP) into metabolizing cells, showing that the cells are depolarized. A steep decrease in this rate was found even at low cation concentrations, reaching 62%, 42%, 58%, 40% and 40% at high concentrations of K+, Rb+, Cs+, Na+ and Li+, respectively. The corresponding concentrations at which half-maximum decrease was found were 0.22, 0.36, 1.2, 17 and 17 mM. These values are of the same order of magnitude as the half-saturation concentrations for monovalent cation uptake by the yeast.     

Effects of temperature variation and phenethyl alcohol addition on acyl chain order and lipid organization in Escherichia coli derived membrane systems. A 2H- and 31P-NMR study.

Using 2H- and 31P-NMR techniques the effects of temperature variation and phenethyl alcohol addition were investigated on lipid acyl chain order and on the macroscopic lipid organization of membrane systems derived from cells of the Escherichia coli fatty acid auxotrophic strain K1059, which was grown in the presence of [11,11-2H2]oleic acid. Membranes of intact cells showed a gel to liquid-crystalline phase transition in the range of 4-20 degrees C, which was similar to that observed for the total lipid extract and for the dominant lipid species phosphatidylethanolamine (PE). Phosphatidylglycerol (PG) remained in a fluid bilayer throughout the whole temperature range (4-70 degrees C). At 30 degrees C acyl chain order was highest in PE, followed by the total lipid extract, PG, intact cells, and isolated inner membrane vesicles. Acyl chain order in E. coli PE and PG was much higher than in the corresponding dioleoylphospholipids. E. coli PE was found to maintain a bilayer organization up to about 60 degrees C, whereas in the total lipid extract as well as in intact E. coli cells bilayer destabilization occurred already at about 42 degrees C. It is proposed that the regulation of temperature at which the bilayer-to-non-bilayer transition occurs may be important for membrane functioning in E. coli. Addition of phenethyl alcohol did not affect the macroscopic lipid organization in E. coli cells or in the total lipid extract, but caused a large reduction in chain order of about 70% at 1 mol% of the alcohol in both membrane systems. It is concluded that while both increasing temperature and addition of phenethyl alcohol can affect membrane integrity, in the former case this is due to the induction of non-bilayer lipid structures, whereas in the latter case this is caused by an increase in membrane fluidity.     

Effects of data smoothing on the reconstruction of helical axis parameters in human joint kinematics

In biomechanical joint-motion analyses, the continuous motion to be studied is often approximated by a sequence of finite displacements, and the Finite Helical Axis (FHA) or "screw axis" for each displacement is estimated from position measurements on a number of anatomical or artificial landmarks. When FHA parameters are directly determined from raw (noisy) displacement data, both the position and the direction of the FHA are ill-determined, in particular when the sequential displacement steps are small. This implies, that under certain conditions, the continuous pathways of joint motions cannot be adequately described. The purpose of the present experimental study is to investigate the applicability of smoothing (or filtering) techniques, in those cases where FHA parameters are ill-determined. Two different quintic-spline smoothing methods were used to analyze the motion data obtained with Roentgenstereophotogrammetry in two experiments. One concerning carpal motions in a wrist-joint specimen, and one relative to a kinematic laboratory model, in which the axis positions are a priori known. The smoothed and non-smoothed FHA parameter errors were compared. The influences of the number of samples and the size of the sampling interval (displacement step) were investigated, as were the effects of equidistant and nonequidistant sampling conditions and noise invariance.     

Design optimization of a prosthesis stem reinforcing shell in total hip arthroplasty

The use of a perforated, titanium funicular shell to support the proximal femoral cortex in total hip arthroplasty was evaluated with the aid of both analytical and numerical techniques. The principal interactions between the femoral cortex, the metal shell, the implant stem and the acrylic bone cement were modeled using beam on elastic foundations theory and two-dimensional elasticity theory. Subsequent formulation of this model as a nonlinear design optimization problem enabled the determination of the dimensions of the implant and reinforcing shell which minimized an objective function based on a simplified material failure criterion. Two cases were examined, each with two cervico-diaphyseal angles: case A: with a rigid contact between a proximal prosthesis collar and the calcar femorale and case B: no collar contact (a collarless prosthesis or post-operative loosening). Case A achieved an optimal solution at a stem diameter 11-23 percent of the cortex inner diameter, a stem length to diameter ratio of 12-40, shell diameter 22-53 percent and thickness 0.2-7.2 percent of the cortex inner diameter and thickness, respectively. Case B achieved an optimal solution at a stem diameter 67-92 percent of the cortex inner diameter, length to diameter ratio of 4-6, and no shell. In case A the collar support makes the type of internal fixation unimportant, while in the more realistic case B, the shell is not recommended.     

Cholesterol as a target for toxins

A mechanism is proposed for the way in which cholesterol facilitates channel formation by polyene antibiotics and bacterial protein toxins. Central elements of the model are: (i) interactions between the ring system of the sterol and rigid elements of the polyene or toxin molecule, and (ii) the specific orientation of cholesterol within the membrane.     

The surface free energy of Leishmania mexicana amazonensis.

Surface charge of Leishmania mexicana amazonensis was investigated by direct zeta-potential determination and ultrastructural cytochemistry, and its surface tension was studied by measurements of the advancing contact angle formed by the parasite monolayers with drops of liquids of different polarities. Both virulent and avirulent promastigotes exhibited negatively charged surfaces with a zeta-potential of about -15 mV. Treatment of these cells with trypsin, alkaline phosphatase, or phospholipase C rendered their surfaces less negatively charged, whereas neuraminidase did not alter the parasite negativeness. Cytochemically, we could observe a reduction in the cationized ferritin binding after the parasite treatment with each of the former enzymes, but not with neuraminidase. The surface free energy of parasites was calculated by taken to account the London dispersion, the Keeson dipole-dipole, and the Debye dipole-induced forces, as well as the surface polarity of the parasites and their zeta-potentials, by considering their adhesion to polystyrene surfaces. The delta G values of -6.4 and -18.1 mJ.m-2 were obtained for avirulent and virulent promstigotes, respectively.     

N-terminally extended substance P is released together with substance P from rat spinal cord.

The release of different forms of substance P-like immunoreactivity (SP-LI) from superfused slices of rat spinal cord was studied. The released SP-LI was characterized by reverse-phase high-performance liquid chromatography and radioimmunoassay with two antisera directed to the C- and N-terminal parts of SP, respectively. The SP-LI detected in the superfusates with the C-terminally directed antiserum was found to consist of (undeca) SP, SP-sulfoxide and a late eluting component which was not detectable with the N-terminally directed antiserum. This component was also found in neutral extracts of the spinal cord. Upon trypsin digestion, it produced SP-LI detectable with both C- and N-terminally directed antiserum which also coeluted with SP. From these results we conclude that this form of SP-LI most likely corresponds to an N-terminally extended form of SP. An increase of the potassium concentration in the superfusion fluid from 5 to 50 mM evoked an increased overflow of both SP and the N-terminally extended SP. The present results indicate that N-terminally extended SP is released by a calcium-dependent mechanism together with SP from terminals in the spinal cord in response to potassium stimulation.     

Mineralocorticoids modify rat liver delta 6 desaturase activity and other parameters of lipid metabolism

The changes in linoleyl-CoA desaturase activity of rat liver microsomes were studied after a single intraperitoneal injection of 11-deoxycorticosterone or aldosterone at physiological doses. Fatty acid of plasma and different liver fractions, and physical properties of microsomal membranes were also investigated. It was found that the specific activity of delta 6 desaturase decreased 4-fold 24 hr after the injection of aldosterone or deoxycorticosterone. Pretreatment of the rats with aldosterone led to a significant decrease in the percent distribution of palmitic, arachidonic, docosapentaenoic and docosahexenoic acids, with a concomitant increase in palmitoleic, oleic and linoleic acids in plasma and liver homogenates, microsomes and cytosol fractions. A similar pattern was observed after deoxycorticosterone administration. The changes resulted in a decreased unsaturation index of all fractions studied and were well-correlated with the increase observed in fluorescence depolarization of the hydrophobic probe 1,6-diphenylhexatriene in liver microsomal membranes. The interlipid and lipid/protein ratios in microsomes remained constant after hormonal treatment. These results are consistent with the idea that the inhibition of delta 6 desaturase activity and the alterations in fatty acid composition induced by mineralocorticoids, are solely responsible for the measured decrease in liver microsomal membrane fluidity.     

Redescription de Proteocephalus paraguayensis (Rudin, 1917) (Cestoda: Proteocephalidae) parasite de Hydrodynastes gigas (Dum., Bibr. & Dum., 1854) du Paraguay

Redescripción de Proteocephalus paraguayensis (Rudin, 1917) (Cestoda: Proteocephalidae), parásito de Hydrodynastes gigas (Dum., Bibr. & Dum., 1854) de Paraguay. Se describe esta especie notable, considerada por Freze (1965) como species inquirenda. Si comparamos esta especie con otras especies de Proteocephalidea, veremos que ella presenta caracteres anatomo-morfológicos propios. Esta especie se caracteriza por: vitelógenos de posición dorsal, adosados a la musculatura interna longitudinal, desbordando en parte sobre el córtex y la médula; formación particular del útero; posición cortical del tronco uterino y medular de los divertículos uterinos; esfínter vaginal proximal; cirro muy alargado; glándula de Mehlis muy desarrollada. Consideramos P. paraguayensis como una especie válida y presumimos que el huesped-tipo es Hydrodynastes gigas (Dum., Bibr. & Dum., 1854). A pesar de las características que posee P. paraguayensis, pensamos que no es oportuno clasificar esta especie en un nuevo género monotípico. Proteocephalus paraguayensis, considered by Freze (1965) as a species inquirenda, is redescribed and figured. When compared with other members of the Proteocephalidea, the species shows the following morpho-anatomical characters: the vitelline follicles in a dorsal position, attached to the internal longitudinal musculature and extending into both the cortex and medulla; a characteristic formation of the uterus; the uterine stem in a cortical position and uterine branches in a medullary position; a proximal vaginal sphincter; a very elongate cirrus; and very large Mehlis' glands. The specific status of Proteocephalus paraguayensis is confirmed. Our specimens were taken from Hydrodynastes gigas (the host according to Rudin was Coluber sp.). Even though the species differs significantly from other proteocephalideans, its systematic and phylogenetic position is not yet clearly demonstrated, and it is decided to refrain from attributing it to a new genus.