An electrostatic mechanism for Ca(2+)-mediated regulation of gap junction channels.

Gap junction channels mediate intercellular signalling that is crucial in tissue development, homeostasis and pathologic states such as cardiac arrhythmias, cancer and trauma. To explore the mechanism by which Ca(2+) blocks intercellular communication during tissue injury, we determined the X-ray crystal structures of the human Cx26 gap junction channel with and without bound Ca(2+). The two structures were nearly identical, ruling out both a large-scale structural change and a local steric constriction of the pore. Ca(2+) coordination sites reside at the interfaces between adjacent subunits, near the entrance to the extracellular gap, where local, side chain conformational rearrangements enable Ca(2+)chelation. Computational analysis revealed that Ca(2+)-binding generates a positive electrostatic barrier that substantially inhibits permeation of cations such as K(+) into the pore. Our results provide structural evidence for a unique mechanism of channel regulation: ionic conduction block via an electrostatic barrier rather than steric occlusion of the channel pore

Lines, Circles, Planes and Spheres

Let $S$ be a set of $n$ points in $\mathbb{R}^3$, no three collinear and not all coplanar. If at most $n-k$ are coplanar and $n$ is sufficiently large, the total number of planes determined is at least $1 + k \binom{n-k}{2}-\binom{k}{2}(\frac{n-k}{2})$. For similar conditions and sufficiently large $n$, (inspired by the work of P. D. T. A. Elliott in \cite{Ell67}) we also show that the number of spheres determined by $n$ points is at least $1+\binom{n-1}{3}-t_3^{orchard}(n-1)$, and this bound is best possible under its hypothesis. (By $t_3^{orchard}(n)$, we are denoting the maximum number of three-point lines attainable by a configuration of $n$ points, no four collinear, in the plane, i.e., the classic Orchard Problem.) New lower bounds are also given for both lines and circles.Comment: 37 page

A blueprint for integrated eye-controlled environments

Eye-based environmental control requires innovative solutions for supporting effective user interaction, for allowing home automation and control, and for making homes more "attentive" to user needs. Several approaches have already been proposed, which can be seen as isolated attempts to address only partial issues and specific sub-sets of the general problem. This paper aims at tackling gaze-based home automation as a whole, exploiting state of the art technologies and trying to integrate interaction modalities than are currently supported and that may supported in a near future. User-home interaction is sought through two, complementary, interaction patterns: direct interaction and mediated interaction. Integration between home appliances/devices and user interfaces is granted by a central point of abstraction/harmonization called House Manager. Innovative points can be identified in the wide flexibility of the approach which allows on one side to integrate virtually all home devices having a communication interface, and, on the other side, mixes-up direct and mediated user interaction exploiting the advantages of both. A complete discussion about interaction and accessibility issues is provided, justifying the presented approach from the point of view of human-environment interaction