Block of Kcnk3 by protons. Evidence that 2-P-domain potassium channel subunits function as homodimers.

KCNK subunits have two pore-forming P domains and four predicted transmembrane segments. To assess the number of subunits in each pore, we studied external proton block of Kcnk3, a subunit prominent in rodent heart and brain. Consistent with a pore-blocking mechanism, inhibition was dependent on voltage, potassium concentration, and a histidine in the first P domain (P1H). Thus, at pH 6.8 with 20 mm potassium half the current passed by P1H channels was blocked (apparently via two sites approximately 10% into the electrical field) whereas channels with an asparagine substitution (P1N) were fully active. Furthermore, pore blockade by barium was sensitive to pH in P1H but not P1N channels. Although linking two Kcnk3 subunits in tandem to produce P1H-P1H and P1N-P1N channels bearing four P domains did not alter these attributes, the mixed tandems P1H-P1N and P1N-P1H were half-blocked at pH approximately 6.4, apparently via a single site. This implicates a dimeric structure for Kcnk3 channels with two (and only two) P1 domains in each pore and argues that P2 domains also contribute to pore formation

Raison et déraison dans la Lettre de Lord Chandos de Hofmannsthal (suite)

Cette étude se propose trois objectifs. En premier lieu, elle aborde le texte de Hofmannsthal d’une manière traditionnelle afin de montrer les limites de cette approche. En second lieu, elle s’efforce d’appliquer les hypothèses avancées par la sémiotique tensive (Fontanille-Zilberberg), hypothèses qui consistent pour l’essentiel dans la grammaticalisation de la circulation en discours des valences intensives et extensives. Enfin, une leçon émerge, nous semble-t-il, peu à peu, à savoir que l’affectivité ne se tient pas à la périphérie du sens, mais en son coeur même et, pour le dire sans précaution, l’affectivité devient la clef de la rationalité de ce type de discours, c’est-à-dire ce qu’il y a à comprendre dans l’acte de la lecture.This study proposes three goals : First, it examines Hofmannsthal’s text from a traditional point of view to show the limits of such an approach. Secondly, it tries to apply an hypothesis, based on a tensive semiotics (Fontanille-Zilberberg), which describes essentially the grammaticalization of intensive and extensive valences in discursive circulation. Finally, a lesson seems to emerge, little by little, from this reevaluation, and it is, that affectivity does not exist on the periphery of meaning (sense), but lies at its very heart ; and this allows us to say without hesitation that affectivity is the key to the rationality of this kind of discourse. It is, in other words, that which is to be understood in the act of reading

Measuring cotunneling in its wake

We introduce a rate formalism to treat classically forbidden electron transport through a quantum dot (cotunneling) in the presence of a coupled measurement device. We demonstrate this formalism for a toy model case of cotunneling through a single-level dot while being coupled to a strongly pinched-off quantum point contact (QPC). We find that the detector generates three types of back-action: the measurement collapses the coherent transport through the virtual state, but at the same time allows for QPC-assisted incoherent transport, and widens the dot level. Last, we obtain the measured cotunneling time from the cross correlation between dot and QPC currents.Comment: 15 pages, 9 figures, 1 appendix, published versio

Seeing bulk topological properties of band insulators in small photonic lattices

We present a general scheme for measuring the bulk properties of non-interacting tight-binding models realized in arrays of coupled photonic cavities. Specifically, we propose to implement a single unit cell of the targeted model with tunable twisted boundary conditions in order to simulate large systems and, most importantly, to access bulk topological properties experimentally. We illustrate our method by demonstrating how to measure topological invariants in a two-dimensional quantum Hall-like model.Comment: 5 pages, 2 figures; with Supplemental Material (2 pages