IgE-mediated degranulation of mast cells does not require opening of ion channels

Rat peritoneal mast cells respond to antigenic stimulation by releasing histamine through exocytosis. The dynamics of exocytosis can be investigated by dialysing single cells with patch pipettes using the whole-cell recording configuration of the patch-clamp technique. However, dialysed cells fail to respond to external stimuli such as compound 48/80 or antigens, suggesting that essential cytoplasmic components have been washed out. We have developed a new patch-clamp configuration in which the patch under the pipette tip is not disrupted but instead permeabilized, preventing the diffusion of large molecules out of the cell. In this configuration the cell responds to external stimulation, and the capacitance as well as the conductance of the cell membrane can be recorded during degranulation. On antigenic stimulation, the cell capacitance (proportional to plasma membrane area), after an initial delay, increases by a factor of about 3. This increase in capacitance is often preceded by a transient increase in conductance. Agents that block Ca-activated channels inhibit this conductance change without affecting the amplitude and time course of degranulation. We therefore conclude that, in contrast to excitable secretory cells such as chromaffin cells, mast cells do not use ion channels in stimulus-secretion coupling.     

Reverse engineering of the giant muscle protein titin

Through the study of single molecules it has become possible to explain the function of many of the complex molecular assemblies found in cells. The protein titin provides muscle with its passive elasticity. Each titin molecule extends over half a sarcomere, and its extensibility has been studied both in situ and at the level of single molecules. These studies suggested that titin is not a simple entropic spring but has a complex structure-dependent elasticity. Here we use protein engineering and single-molecule atomic force microscopy to examine the mechanical components that form the elastic region of human cardiac titin. We show that when these mechanical elements are combined, they explain the macroscopic behaviour of titin in intact muscle. Our studies show the functional reconstitution of a protein from the sum of its parts.     

Ca-efflux,from direct membrane injury by CCl4, is elicited by amphiphilic vehicles in vitro

Direct membrane injury by CCl₄, in situations excluding metabolic activation, was evaluated in saponin-permeabilized hepatocytes and in microsomes by measuring immediate Ca²⁺ efflux. A good correlation appears between the Ca²⁺ efflux and the level of CCl₄ in the membrane and also the variations in fluidity. Mixtures of CCl₄ with water-soluble vehicles were used to improve the dispersion of CCl₄ in the medium. The mixtures varied in their ability to elicit the membrane effects of CCl₄. The performance of ethanol and, to a lesser degree, other alcohols, suggests the existence of a water stable structural organization between CCl₄ and these amphiphilic vehicles, facilitating the transfer of CCl₄ to the membrane.     

Metabolism and in vitro binding of several organochlorine and organophosphate pesticides to calf thymus DNA and rat liver microsomal proteins]

The organophosphorus insecticide ethyl-parathion was transformed by rat liver microsomes into metabolites which were bound to calf thymus DNA, in large amount. When the rats were treated by phenobarbital or 3-methylcholanthrene, the metabolite binding to DNA was increased two-fold. By contrast, in the same conditions, the organochlorine insecticides, aldrin, dieldrin and gamma hexachlorocyclohexane (lindane), did not yield metabolites able to bind to DNA and to proteins.     

GSK-3α/β kinases and amyloid production in vivo

Arising from C. J. Phiel, C. A. Wilson, V. M.-Y. Lee & P. S. Klein 423, 435-439 (2003)A major unresolved issue in Alzheimer's disease is identifying the mechanisms that regulate proteolytic processing of amyloid precursor protein (APP)-glycogen synthase kinase-3 (GSK-3) isozymes are thought to be important in this regulation. Phiel et al. proposed that GSK-3α, but not GSK-3β, controls production of amyloid. We analysed the proteolytic processing of mouse and human APP in mouse brain in vivo in five different genetic and viral models. Our data do not yield evidence for either GSK-3α-mediated or GSK-3β-mediated control of APP processing in brain in vivo.