No abstract

The electrical properties of an alamethicin multi-pore system have been studied by voltage-jump current-relaxation experiments (this paper) and by autocorrelation and spectral analysis (following paper). With these methods a slow time constant and a fast time constant were observed which differ by about one to three orders of magnitude depending on the experimental conditions. Steady-state current and time constants were analyzed as functions of voltage, alamethicin concentration and temperature. Within experimental error the data obtained with these different methods are in good agreement. The experimentally measured relation between the voltage and alamethicin concentration dependence of the slow relaxation time fits into a model of an alamethicin pore which adopts consecutive pore states and which decays only from the lowest state. It indicates that the uptake of one alamethicin molecule by the existing pore and, in formal equivalence, the transfer of about one positive elementary charge across the membrane are associated with the transition from a given pore conductance state to the next higher state. From the voltage and alamethicin concentration dependence of the pore formation rate evidence shows that a hexameric preaggregate exists at the membrane interface out of which two to three molecules are simultaneously inserted into the membrane to form the pore nucleus. The effects of different voltage pretreatment on the experimentally determined parameters have been investigated and are discussed in detail.Alamethicin has been shown by Mueller and Rudin (1968), Baumann and Mueller (1974) and Mueller (1976a, b) to be a model substance which induces excitability phenomena in artificial lipid membranes. A way to elucidate the underlying molecular mechanism of alamethicin action has been opened through single channel investigations by Gordon and Haydon (1972)

Atomic force microscopy at high temperature resolution (DeltaT < or approximately 0.1 K) provided a quantitative structural calorimetry of the transition from the fluid (Lalpha)- to the gel (Pbeta')-phase of supported dimyristoylphosphatidylcholine bilayers. Besides a determination of the main transition temperature (T0) and the van't Hoff transition enthalpy (DeltaHvH), the structural analysis in the nm-scale at T close to T0 of the ripple phase allowed an experimental estimation of the area of cooperative units from small lipid domains. Thereby, the corresponding transition enthalpy (DeltaH) of single molecules could be determined. The lipid organization and the corresponding parameters T0 and DeltaHvH (DeltaH) were modulated by heptanol or external Ca2+ and compared with physiological findings. The size of the cooperative unit was not significantly affected by the presence of 1 mM heptanol. The observed linear relationship of DeltaHvH and T0 was discussed in terms of a change in heat capacity.

Two-photon polymerization technique was applied to generate three-dimensional (3D) scaffold-like structures using the photosensitive organic-inorganic hybrid polymer ORMOCER Õ . The structures were studied with respect to potential applications as scaffold for tissue engineering. Cell counting and comet assay, respectively, demonstrated that doubling time and DNA strand breaks of CHO cells, GFSHR-17 granulosa cells, GM-7373 endothelial cells, and SH-SY5Y neuroblastoma cells were not affected by ORMOCER Õ . ORMOCER Õ related alteration of formation of tissue specific cell-to-cell adhesions like gap junctions was ruled out by double whole-cell patch-clamp technique. Additionally, growth of cells on the vertical surfaces of 3D structures composed of ORMOCER Õ is shown.

The concept of purinergic neurotransmission, first proposed by Burnstock, has been confirmed in various cell types. We show here, by the patch-clamp method, that external ATP in micromolar concentrations (1-100 microM) activates cation channels in the membranes of fusion-competent myoblasts and myotubes. In cell-attached membrane patches of myoblasts and myotubes the mean number of simultaneously activated channels increases with time after external ATP application. In myoblasts only one population of channels having a mean single-channel conductance of gamma=43 pS was found, while in myotubes two populations with gamma 1=48 pS and gamma 2=20 pS were observed. Treatment of myotube membranes with acetylcholine (ACh) or carbachol resulted in two populations of channels which had conductance values and voltage-dependent mean channel lifetimes similar to those produced in response to ATP. The results show that embryonic skeletal muscle cells contain cation channels sensitive to ATP and provide evidence for a neurotransmitter-like action of ATP on these cells.