Biomedical subjects

W Knoll

Publications and source records attributed to W Knoll.

75 records · Page 5Linked to original sources

PubMedDate not supplied

An extended kinetic analysis of valinomycin-induced Rb-transport through monoglyceride membranes.

The time course of the current following a voltage jump, which is applied to monoglyceride bilayers in the presence of valinomycin, shows two relaxation times. This is basically in agreement with a simple carrier model which has been described in full detail formerly. Relaxation times and amplitudes allow a calculation of the rate constants of the transport model. The presented data supplement an analysis which was hitherto based only on the slower relaxation process and on information derived from the nonlinearity of current-voltage characteristics. The additional resolution of the faster relaxation time allowed an approximate determination of the voltage dependence of the translocation rate constant for carrier-ion-complex and provided evidence for a small voltage dependence of the interfacial reaction. The dependence of the relaxation parameters on the ion concentration in the aqueous phase was interpreted assuming a saturation of the ion concentration at the reaction plane at high bulk concentrations.

Biological Transport↗

PubMedDate not supplied

Validation of the use of field effect transistors for extracellular signal recording in pharmacological bioassays.

The use of field effect transistors (FETs) in biomedical research has been in rapid progression in recent years. The present study aims to demonstrate a quantitative use of these devices in pharmacological bioassays. FETs were made as a 4 x 4 matrix of gates with a width of 200 microm separating each gate. The surface of the FETs (silicon oxide), covered with a layer of laminin, fibronectin, or nitro cellulose was suitable for cell adhesion. The cultured dissociated cardiac myocytes were spontaneously active within 24 to 48 h after initial plating. Simultaneous intracellular patch clamp recordings were used to verify the electrophysiological signals of cells that were coupled to the gates. All positive chronotropes (isoproterenol, norepinephrine) and negative chronotropes (verapamil, carbamylcholine, SDZ PCO400) showed their characteristic effects on heart cells in terms of changes of beat frequency. As the myocytes were in a complete syncitium on each FET, the cells need not be directly coupled to the gate in order to detect any ionic changes. This enables global cellular responses to be analyzed. The system also offers an opportunity to study the interconnections and communications between different cells. Furthermore, the changes of signal shapes in the presence of different agents could also be detected. The present study demonstrates how versatile and sensitive this recording system is in distinguishing different ionic signal shapes. The authors believe that this system has the potential to replace some currently employed in vitro methods, offering an alternative, which can substantially reduce animal use in pharmacological experiments.

Action Potentials↗

PubMedDate not supplied

The polymer-supported phospholipid bilayer: tethering as a new approach to substrate-membrane stabilization.

We present a new molecular engineering approach in which a polymer-supported phospholipid bilayer is vertically stabilized by controlled covalent tethering at both the polymer-substrate and polymer-bilayer interfaces. This approach is based on lipopolymer molecules, which not only form a polymer cushion between the phospholipid bilayer and a solid glass substrate but also act as covalent connections (tethers) between the bilayer and cushion. Our approach involves Langmuir-Blodgett transfer of a phospholipid-lipopolymer monolayer followed by Schaefer transfer of a pure phospholipid monolayer and is capable of varying the tethering density between the polymer layer and the phospholipid bilayer in a very controlled manner. Further stabilization is achieved if the glass substrate is surface-functionalized with a benzophenone silane. In this case, a photocross-linking reaction between the polymer and benzophenone group allows for the covalent attachment of the polymer cushion to the glass substrate. This approach is similar to that recently reported by Wagner and Tamm in which double tethering is achieved via lipopolymer silanes (Wagner, M. L.; Tamm, L. K. Biophys. J. 2000, 79, 1400). To obtain a deeper understanding of how the covalent tethering affects the lateral mobility of the bilayer, we performed fluorescence recovery after photobleaching (FRAP) experiments on polymer-tethered bilayers at different tethering densities (lipopolymer/phospholipid molar ratios). The FRAP data clearly indicate that the hydrophobic lipopolymer moieties act as rather immobile obstacles within the phospholipid bilayer, thereby leading to hindered diffusion of phospholipids. Whereas the high lateral diffusion coefficient of D = 17.7 mum(2)/s measured at low tethering density (5 mol % lipopolymer) indicates rather unrestricted motion within the bilayer, corresponding values at moderate (10 mol % lipopolymer) and high (30 mol % lipopolymer) tethering densities of D = 9.7 mum(2)/s and D = 1.1 mum(2)/s, respectively, show significant hindered diffusion. These results are contrary to the recent findings on similar membrane systems reported by Wagner and Tamm in which no significant change in phospholipid diffusion was found between 0 and 10 mol % lipopolymer. Our experimental report leads to a deeper understanding of the complex problem of interlayer coupling and offers a path toward a compromise between stability of the whole system and lateral mobility within the bilayer. Furthermore, the FRAP measurements show that polymer-tethered membranes are very interesting model systems for studying problems of restricted diffusion within two-dimensional fluids.

Diffusion↗