Flux ratios and pump stoichiometries at sites II and III in liver mitochondria. Effect of slips and leaks.

Addition of bovine serum albumin to state 4 mitochondria results in a depression of the proton leak and of the resting respiration of 70 and 25%, respectively. The conductance membrane potential diagram, both in the ohmic and in the non-ohmic region, shows that in the presence of bovine serum albumin the level of ohmic conductance is lowered while that of non-ohmic conductance is increased toward higher delta psi values. The same effect is observed during operation of the different proton pumps. Addition of chloroform affects the conductance membrane potential diagram in the following manner: there is no effect in the ohmic region with all pumps, while there is an effect in the non-ohmic region either at site III or at sites II plus III but not at site II. This suggests a possible effect of chloroform at the level of the cytochrome oxidase proton pump. During titration with oligomycin of the ATPase proton pump the conductance potential diagram shows a region of non-ohmicity only in the presence but not in the absence of an ATP-regenerating system. Protonophoric uncouplers such as carbonyl cyanide p(trifluoromethoxy)phenylhydrazone and intrinsic uncouplers such as chloroform have different effects on the relationship between rates of charge translocation and of oxygen consumption, and thus on the pump stoichiometries, in that the slope of the diagram is modified by the latter but not by the former. The differential effects of protonophores and of intrinsic uncouplers on the stoichiometries have been analyzed by computer simulations and represent an additional criterion to distinguish between extrinsic and intrinsic mechanisms of uncoupling

Modal Gating of Human CaV2.1 (P/Q-type) Calcium Channels: I. The Slow and the Fast Gating Modes and their Modulation by β Subunits

The single channel gating properties of human CaV2.1 (P/Q-type) calcium channels and their modulation by the auxiliary β1b, β2e, β3a, and β4a subunits were investigated with cell-attached patch-clamp recordings on HEK293 cells stably expressing human CaV2.1 channels. These calcium channels showed a complex modal gating, which is described in this and the following paper (Fellin, T., S. Luvisetto, M. Spagnolo, and D. Pietrobon. 2004. J. Gen. Physiol. 124:463–474). Here, we report the characterization of two modes of gating of human CaV2.1 channels, the slow mode and the fast mode. A channel in the two gating modes differs in mean closed times and latency to first opening (both longer in the slow mode), in voltage dependence of the open probability (larger depolarizations are necessary to open the channel in the slow mode), in kinetics of inactivation (slower in the slow mode), and voltage dependence of steady-state inactivation (occurring at less negative voltages in the slow mode). CaV2.1 channels containing any of the four β subtypes can gate in either the slow or the fast mode, with only minor differences in the rate constants of the transitions between closed and open states within each mode. In both modes, CaV2.1 channels display different rates of inactivation and different steady-state inactivation depending on the β subtype. The type of β subunit also modulates the relative occurrence of the slow and the fast gating mode of CaV2.1 channels; β3a promotes the fast mode, whereas β4a promotes the slow mode. The prevailing mode of gating of CaV2.1 channels lacking a β subunit is a gating mode in which the channel shows shorter mean open times, longer mean closed times, longer first latency, a much larger fraction of nulls, and activates at more positive voltages than in either the fast or slow mode

Tyr682 in the Aβ-precursor protein intracellular domain regulates synaptic connectivity, cholinergic function, and cognitive performance.

Processing of Aβ-precursor protein (APP) plays an important role in Alzheimer's disease (AD) pathogenesis. The APP intracellular domain contains residues important in regulating APP function and processing, in particular the 682YENPTY687 motif. To dissect the functions of this sequence in vivo, we created an APP knock-in allele mutating Y682 to Gly (APP(YG/YG) mice). This mutation alters the processing of APP and TrkA signaling and leads to postnatal lethality and neuromuscular synapse defects when expressed on an APP-like protein 2 KO background. This evidence prompted us to characterize further the APP(YG/YG) mice. Here, we show that APP(YG/YG) mice develop aging-dependent decline in cognitive and neuromuscular functions, a progressive reduction in dendritic spines, cholinergic tone, and TrkA levels in brain regions governing cognitive and motor functions. These data are consistent with our previous findings linking NGF and APP signaling and suggest a causal relationship between altered synaptic connectivity, cholinergic tone depression and TrkA signaling deficit, and cognitive and neuromuscular decline in APP(YG/YG) mice. The profound deficits caused by the Y682 mutation underscore the biological importance of APP and indicate that APP(YG/YG) are a valuable mouse model to study APP functions in physiological and pathological processes

Multiplicity Studies and Effective Energy in ALICE at the LHC

In this work we explore the possibility to perform ``effective energy'' studies in very high energy collisions at the CERN Large Hadron Collider (LHC). In particular, we focus on the possibility to measure in $pp$ collisions the average charged multiplicity as a function of the effective energy with the ALICE experiment, using its capability to measure the energy of the leading baryons with the Zero Degree Calorimeters. Analyses of this kind have been done at lower centre--of--mass energies and have shown that, once the appropriate kinematic variables are chosen, particle production is characterized by universal properties: no matter the nature of the interacting particles, the final states have identical features. Assuming that this universality picture can be extended to {\it ion--ion} collisions, as suggested by recent results from RHIC experiments, a novel approach based on the scaling hypothesis for limiting fragmentation has been used to derive the expected charged event multiplicity in $AA$ interactions at LHC. This leads to scenarios where the multiplicity is significantly lower compared to most of the predictions from the models currently used to describe high energy $AA$ collisions. A mean charged multiplicity of about 1000-2000 per rapidity unit (at $\eta \sim 0$) is expected for the most central $Pb-Pb$ collisions at $\sqrt{s_{NN}} = 5.5 TeV$.Comment: 12 pages, 19 figures. In memory of A. Smirnitski

Study of single muons with the Large Volume Detector at Gran Sasso Laboratory

The present study is based on the sample of about 3 mln single muons observed by LVD at underground Gran Sasso Laboratory during 36500 live hours from June 1992 to February 1998. We have measured the muon intensity at slant depths from 3 km w.e. to 20 km w.e. Most events are high energy downward muons produced by meson decay in the atmosphere. The analysis of these muons has revealed the power index of pion and kaon spectrum: 2.76 \pm 0.05. The reminders are horizontal muons produced by the neutrino interactions in the rock surrounding LVD. The value of this flux is obtained. The results are compared with Monte Carlo simulations and the world data.Comment: 13 pages, 2 figures, accepted for publication in "Physics of Atomic Nuclei

The INFN-grid testbed

The Italian INFN-Grid Project is committed to set-up, run and manage an unprecedented nation-wide Grid infrastructure. The implementation and use of this INFN-Grid Testbed is presented and discussed. Particular care and attention are devoted to those activities, relevant for the management of the Testbed, carried out by the INFN within international Grid Projects

Upper Limit on the Prompt Muon Flux Derived from the LVD Underground Experiment

We present the analysis of the muon events with all muon multiplicities collected during 21804 hours of operation of the first LVD tower. The measured depth-angular distribution of muon intensities has been used to obtain the normalization factor, A, the power index, gamma, of the primary all-nucleon spectrum and the ratio, R_c, of prompt muon flux to that of pi-mesons - the main parameters which determine the spectrum of cosmic ray muons at the sea level. The value of gamma = 2.77 +/- 0.05 (68% C.L.) and R_c < 2.0 x 10^-3 (95% C.L.) have been obtained. The upper limit to the prompt muon flux favours the models of charm production based on QGSM and the dual parton model.Comment: 10 pages, 4 figures, RevTex. To appear in Phys. Rev.

Muon `Depth -- Intensity' Relation Measured by LVD Underground Experiment and Cosmic-Ray Muon Spectrum at Sea Level

We present the analysis of the muon events with all muon multiplicities collected during 21804 hours of operation of the first LVD tower. The measured angular distribution of muon intensity has been converted to the `depth -- vertical intensity' relation in the depth range from 3 to 12 km w.e.. The analysis of this relation allowed to derive the power index, $\gamma$, of the primary all-nucleon spectrum: $\gamma=2.78 \pm 0.05$. The `depth -- vertical intensity' relation has been converted to standard rock and the comparison with the data of other experiments has been done. We present also the derived vertical muon spectrum at sea level.Comment: 7 pages, 3 figures, to be published on Phys. Rev.

Study of QGP signatures with the phi->K+K- signal in Pb-Pb ALICE events

The phi->K+K- decay channel in Pb-Pb collisions at LHC is studied through a full simulation of the ALICE detector. The study focuses on possible signatures in this channel of quark-gluon plasma (QGP) formation. On a basis of 10^6 collisions at high centrality some proposed QGP signatures are clearly visible both in K+K- invariant mass and transverse mass distributions. The high significance of this observation appears to reside heavily on the use of the TOF (Time Of Flight) system of ALICE in addition to its central tracking detectors.Comment: 9 pages, 7 figures, to appear in EPJ