Biomedical subjects
Publications and source records attributed to R Benz.
Mycobacterial retropharyngeal abscesses are usually secondary to cervical tuberculous osteomyelitis. A case is presented of a retropharyngeal abscess that was caused by the atypical mycobacteria with no mucous membrane or cervical spine involvement. The operative and medical management is discussed.
The cyclic dodecapeptide PV, cyclo-(D-Val-L-Pro-L-Val-D-Pro)3, a structural analogue of the ion-carrier valinomycin, increases the cation permeability of lipid bilayer membranes. This paper reports the results of two types of relaxation experiments, namely relaxation of the membrane current after a voltage jump and decay of the membrane voltage after a charge pulse in lipid bilayer membranes exposed to PV. From the relaxation data, the rate constant for the translocation of the ion carrier complex across the membrane, as well as the partition coefficient of the complex between water and membrane solution interface were computed and found to be about one order of magnitude less than the comparable values for valinomycin (Val). Furthermore, the dependence of the initial membrane conductivity on ion concentration was used to evaluate the equilibrium constant, K, of complexation between PV and some monovalent cations in water. The values of K yield the following selectivity sequence of PV: Na+ less than NH4+ less than K+ less than Cs+ less than Rb+. These and earlier results are consistent with the idea that PV promotes cation movement across membranes by the solution complexation mechanism which involves complexation between ion and carrier in the aqueous phase and transport of the carrier across the membrane. In the particular form of the solution complexation mechanism operating here, the PV present in the PV-cation complex carrying charge across the membrane derives from the side from which the current is flowing (cis-mechanism). As shown previously, valinomycin, in contrast to PV, acts by an interfacial complexation mechanism in which the Val in the Val-cation complex derives from the side toward which current is flowing (trans-mechanism). The comparison of the kinetic properties of these two closely related compounds yields interesting insights into the relationship between chemical structure and function of ion carriers.
A modified version of the charge-pulse relaxation technique with improved time resolution was applied to the study of transport kinetics of hydrophobic ions (tetraphenylborate, dipicrylamine) through lipid bilayer membranes. Besides a better time resolution the charge-pulse method has the additional advantage that the perturbation of the membrane can be kept small (voltage amplitudes between 1 and 10 mV). The results of the analysis support the model proposed earlier, according to which the overall transport takes place in three consecutive steps, adsorption of the ion from water to the interface, translocation to the opposite interface, and desorption into the aqueous phase. The translocation rate constant ki and the partition coefficient gamma of the hydrophobic ion between water and the membrane were measured for lecithins with different mono-unsaturated fatty acid residues. Increasing the chain length of the fatty acid from C16 to C24 resulted in a decrease of ki by a factor of about 9 in the case of tetraphenylborate and by a factor of about 17 in the case of dipicrylamine.
The specific capacity of black lipid membranes of different phospholipids dissolved in n-alkanes was investigated. The hydrocarbon thickness of these membranes, as calculated from the electric capacity with a dielectric constant of 2.1, was in most cases close to 5 nm. It was found that the specific capacity is not constant with time after blackening. It shows a linear time dependence characteristic for each lipid/solvent system. The influence of a transmembrane potential on the capacity of the membranes was measured. It was shown that the extent of the capacity change, obtained 10 s after applying a voltage, was strongly dependent on the lipid composition as well as the solvent content of the membranes. The capacity change of the membranes seems to be caused mainly by a thickness change and not by an area increase of the membranes.
The charge-pulse technique has been used previously for the study of quasi-stationary processes in membranes which required only a moderate time resolution. It is shown here that a time resolution of about 400 nsec may be achieved with this technique and that it may be applied to the kinetic analysis of carrier-mediated ion transport. By this method we have studied the transport of alkali ions through optically black monoolein membranes in the presence of the ion carrier valinomycin. All three relaxation processes that are predicted by theory have been resolved. From the relaxation times and the relaxation amplitudes the rate constants for the association (kR) and the dissociation (kD) of the ion-carrier complex, as well as the translocation rate constants of the complex (kMS) and the free carrier (kS) could be obtained. For 1 M Rb+ at 25 degrees C the values are kR=3 x 10(5) M(-1) sec(-1), kD=2 x 10(5) sec (-1), kMS=3 x 10(5) sec(-1), kS=4 x 10(4) sec(-1). The activation energies of the single rate constants which have been estimated from experiments at two different temperatures range between 50 and 90kJ/mol.
The thickness changes of black lipid membranes of different composition after a voltage jump were investigated. In a second series of electrical relaxation experiments the kinetics of channel formation by gramicidin A were measured. The time course of the membrane current was compared with the time course of the thickness change of the membranes. We found that the time course of the current as a consequence of channel formation by gramicidin A did not correlate with the thickness change of the lipid membranes. A possible direct influence of the electric field is discussed.
Explore the source record for details and available documents.
Planar bilayer membranes were formed from monolayers of a series of mono-unsaturated monoglycerides and lecithins. The hydrocarbon thickness of these membranes, as calculated from the electrical capacity, increases with the length of the fatty acid chain. The specific capacity of monoolein bilayers was found to be 0.745 muF/cm-2 which is nearly twice that of a monoolein black film made in the presence of decane, but is close to that obtained after freezing out the solvent from the black film. The hydrocarbon thickness of the bilayer, as calculated with a dielectric constant of 2.1, is considerably less than twice the length of the extended hydrocarbon chain of the monoglyceride. The specific capacity (Cm) of bilayers made from monoolein monolayers showed a negligible voltage dependence, whereas the Cm increased significantly at a voltage of 150 mV in the case of Mueller-Rudin-type monoolein films with n-decane as a solvent.
Ion transport across lipid bilayer membranes in the presence of macrotetrolide antibiotics has been studied by stationary conductance and nonstationary relaxation methods. The results are discussed on the basis of a carrier model which has already been successfully applied to valinomycin induced ion transport. Again a kinetic analysis has been performed from which the single rate constants of the carrier model could be derived. In addition the equilibrium constant of complex formation in the aqueous phase could be determined. Measurements have been made for 4 macrotetrolides, for several ions and for various chain lengths of the lipid molecules composing the membrane.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Electrical relaxation experiments have been performed with phosphatidylinositol bilayer membranes in the presence of the ion carrier valinomycin. After a sudden change of the voltage a relaxation of the membrane current with a time constant of about 20 musec is observed. Together with previous stationary conductance data, the relaxation amplitude and the relaxation time are used to evaluate the rate constants of valinomycin-mediated potassium transport across the lipid membrane. It is found that the rate constants of translocation of the free carrier S and the carrier-ion complex MS(+) are nearly equal (2.10(4) sec(-1)) and are of the same order as the dissociation rate constant of MS(+) in the membrane-solution interface (5.10(4) sec(-1)). The equilibrium constant of the heterogeneous association reaction M(+) (solution) + S (membrane) --> MS(+) (membrane) is found to be approximately 1 M(-1), about 10(6) times smaller than the association constant in ethanolic solution.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
OmpC, one of the major outer membrane proteins of Yersinia enterocolitica, was isolated and purified to homogeneity. When solubilized at room temperature, this protein appeared on SDS polyacrylamide gel electrophoresis as an oligomer. After heating to the temperature of boiling water, the apparent molecular weight of the monomer was 36,000. The incorporation of purified OmpC into black lipid membranes resulted in an increase in membrane conductance demonstrating pore-forming activity. The reconstituted pores exhibited the characteristics of general diffusion pores. They showed cation selectivity and had a single channel conductance of 1.3 nS in 1.0 M KCl. Assuming a constant diameter of the pore, a length of 6 nm (the width of the outer membrane) and the same ion conductivity inside and outside the pore, the diameter of the pore protein was estimated as 1.0 nm. Polyclonal antibodies were raised against the native, pore-forming protein preparation. These antibodies did not recognize the denatured form of the protein, but cross-reacted with native OmpC and OmpF of Escherichia coli. The regulation of OmpC expression in Y. enterocolitica was dependent on the osmolarity of the medium in the same way as in E. coli.
A cross-sectional analysis was performed to determine risk factors associated with hypertension in 1,238 chronic hemodialysis patients upon enrollment into the HEMO Study. The mean pre- and post-dialysis systolic blood pressure were 152.4 +/- 25.0 (mean +/- SD) and 137.8 +/- 24.6 mm Hg, respectively. The mean pre- and post-dialysis diastolic blood pressures were 82.1 +/- 14.8 and 74.7 +/- 13.8 mm Hg, respectively. Less than 30% of the study cohort had blood pressures that were normotensive by JNC VI guidelines. Risk factors associated with higher pre- and post-dialysis systolic blood pressures included the presence of diabetes mellitus, older age, increased number of prescribed antihypertensive medications, lower hematocrit, and absence of arrhythmias. Variables associated with higher pre- and post-dialysis diastolic blood pressures included younger age, increased number of prescribed anti-hypertensive medications and absence of arrhythmias. There was also a nonlinear relationship between blood pressure and prescribed total ultrafiltration volume. A total ultrafiltration volume of >2.5 kg was associated with an elevation in pre-dialysis systolic and diastolic blood pressures. A total ultrafiltration volume of < or =2.5 kg was associated with an elevation in post-dialysis systolic and diastolic blood pressures. These data on ultrafiltration volume suggest that higher pre-dialysis blood pressures may be associated with excessive interdialytic weight gains due to patient noncompliance with fluid restriction and that higher post-dialysis blood pressures may be associated with a prescribed dry weight that is higher than the patient's true dry weight. Better management of these parameters may improve the prevalence and severity of hypertension in this population.
With the aid of two commercially available analysis programmes we effected non-invasive assessment of the risk for Down's syndrome in 597 pregnancies with healthy fetuses and in 22 pregnancies with trisomie 21-affected fetuses, maternal age ranging between 18 and 45 years. Based on the women's serum levels, hormone concentrations of AFP, free estriol and beta HCG were determined, a multiple of their median was combined with the age factor, and the result used as a parameter for overall risk estimation. A risk cut-off-level greater then 1:250 was considered to represent a positive risk. For patients younger than 35 years test sensitivity, at just over 50%, was found to be low. For those aged 35 years or greater, however, the Dermalog programme was able to detect 94.4% and the Alpha programme 88.2% of fetuses affected by trisomy 21, with a false-positive rate of 19.6 and 19.1%, respectively. If the test were to be applied to all pregnant women beyond 35 years of age the detection rate of Down's syndrome could be nearly doubled compared to today's figure (only 50%, of women in this age group undergo amniocentesis). By the same token the rate of amniocentesis-induced abortion (approx. 1%) could be reduced to about one third.