The dependence of the conductance of the hemocyanin channel on applied potential and ionic concentration with mono- and divalent cations

Studies of mitochondrial porin incorporation parameters and voltage-gated mechanism with different black lipid membranes

Our work in general aims to clarify the mechanism of what can be considered as a process of the kinetics of porin incorporation into bilayer planar membranes and to identify the parameters involved. In this paper, we report the results of systematically investigating the kinetics of porin incorporation into bilayer membranes made up of phosphatidylinositol or oxidized cholesterol using a simple and low-cost ac method. By means of a mathematical model, we provide evidence that two concurrent processes are present during the kinetics which can be interpreted as positive/negative cooperativity, and we investigate the parameters' dependence on external applied voltages. We observed a phase transition (or similar phenomenon) which seems to take place during the insertion process. The conductance measurement obtained by using data at the steady state conditions, provided indirect indications of two possible gating mechanisms.

Pore formation by the sea anemone cytolysin equinatoxin II in red blood cells and model lipid membranes

The interaction of Actinia equina equinatoxin II (EqT-II) with human red blood cells (HRBC) and with model lipid membranes was studied. It was found that HRBC hemolysis by EqT-II is the result of a colloid-osmotic shock caused by the opening of toxin-induced ionic pores. In fact, hemolysis can be prevented by osmotic protectants of adequate size. The functional radius of the lesion was estimated to be about 1.1 nm. EqT-II increased also the permeability of calcein-loaded lipid vesicles comprised of different phospholipids. The rate of permeabilization rised when sphingomyelin was introduced into the vesicles, but it was also a function of the pH of the medium, optimum activity being between pH 8 and 9; at pH 10 the toxin became markedly less potent. From the dose-dependence of the permeabilization it was inferred that EqT-II increases membrane permeability by forming oligomeric channels comprising several copies of the cytolysin monomer. The existence of such oligomers was directly demonstrated by chemical cross-linking. Addition of EqT-II to one side of a planar lipid membrane (PLM) increases the conductivity of the film in discrete steps of defined amplitude indicating the formation of cation-selective channels. The conductance of the channel is consistent with the estimated size of the lesion formed in HRBC. High pH and sphingomyelin promoted the interaction even in this system. Chemical modification of lysine residues or carboxyl groups of this protein changed the conductance, the ion selectivity and the current-voltage characteristic of the pore, suggesting that both these groups were present in its lumen.

Electrical properties of ionic channels formed by Helix pomatia hemocyanin in planar lipid bilayers

Helix pomatia hemocyanin forms ion-conducting channels in planar lipid bilayer membranes when added at mg/ml concentration. These channels have several original features. They fluctuate between one conducting and some poorly conducting states and fluctuations can be grouped in bursts. Different channels can have widely different conductance amplitudes. Both channel conductance and burst lifetime are dependent on the applied voltage. Fluctuations within a burst show a complex kinetic behaviour which has been explained developing a multistate model. The model calls for one single open state and six different closed states. Transitions are allowed only between one of the closed states and the open one and obey first order kinetics. This model is able to fit all our experimental curves obtained in single channel experiments.