Collis Leon P.

No Thumbnail Available
Last Name
Collis
First Name
Leon P.
ORCID

Filters

2007 - 2009 2 2010 - 2011 2
3 1
4
Reset filters

Settings

Search Results

Now showing 1 - 4 of 4
  • Preprint
    Bcl-xL regulates metabolic efficiency of neurons through interaction with the mitochondrial F1FO ATP synthase
    ( 2011-06) Alavian, Kambiz N. ; Li, Hongmei ; Collis, Leon P. ; Bonanni, Laura ; Zeng, Lu ; Sacchetti, Silvio ; Lazrove, Emma ; Nabili, Panah ; Flaherty, Benjamin ; Graham, Morven ; Chen, Yingbei ; Messerli, Shanta M. ; Mariggio, Maria A. ; Rahner, Christoph ; McNay, Ewan ; Shore, Gordon ; Smith, Peter J. S. ; Hardwick, J. Marie ; Jonas, Elizabeth A.
    Anti-apoptotic BCL-2 family proteins such as Bcl-xL protect cells from death by sequestering apoptotic molecules, but also contribute to normal neuronal function. We find in hippocampal neurons that Bcl-xL enhances the efficiency of energy metabolism. Our evidence suggests that Bcl-xL interacts directly with the beta subunit of the F1FO ATP synthase, decreasing an ion leak within the F1FO ATPase complex and thereby increasing net transport of H+ by F1FO during F1FO ATPase activity. By patch clamping submitochondrial vesicles enriched in F1FO ATP synthase complexes, we find that, in the presence of ATP, pharmacological or genetic inhibition of Bcl-xL increases the membrane leak conductance. In addition, recombinant Bcl-xL protein directly increases ATPase activity of purified synthase complexes, while inhibition of endogenous Bcl-xL decreases F1FO enzymatic activity. Our findings suggest that increased mitochondrial efficiency contributes to the enhanced synaptic efficacy found in Bcl-xL expressing neurons.
  • Preprint
    Ion trapping with fast-response ion-selective microelectrodes enhances detection of extracellular ion channel gradients
    ( 2008-11) Messerli, Mark A. ; Collis, Leon P. ; Smith, Peter J. S.
    Previously, functional mapping of channels has been achieved by measuring the passage of net charge and of specific ions with electrophysiological and intracellular fluorescence imaging techniques. However, functional mapping of ion channels using extracellular ion-selective microelectrodes has distinct advantages over the former methods. We have developed this method through measurement of extracellular K+ gradients caused by efflux through Ca2+-activated K+ channels expressed in Chinese hamster ovary cells. We report that electrodes constructed with short columns of a mechanically stable K+-selective liquid membrane respond quickly and measure changes in local [K+] consistent with a diffusion model. When used in close proximity to the plasma membrane (<4 μm), the ISMs pose a barrier to simple diffusion, creating an ion trap. The ion trap amplifies the local change in [K+] without dramatically changing the rise or fall time of the [K+] profile. Measurement of extracellular K+ gradients from activated rSlo channels shows that rapid events, 10–55 ms, can be characterized. This method provides a noninvasive means for functional mapping of channel location and density as well as for characterizing the properties of ion channels in the plasma membrane.
  • Preprint
    Windows to cell function and dysfunction : signatures written in the boundary layers
    ( 2010-01-26) Smith, Peter J. S. ; Collis, Leon P. ; Messerli, Mark A.
    The medium surrounding cells either in culture or in tissues contains a chemical mix varying with cell state. As solutes move in and out of the cytoplasmic compartment they set up characteristic signatures in the cellular boundary layers. These layers are complex physical and chemical environments whose profiles both reflect cell physiology and provide conduits for intercellular messaging. Here we review some of the most relevant characteristics of the extracellular/intercellular space. Our initial focus is primarily with cultured cells but we extend our consideration to the far more complex environment of tissues and discuss how chemical signatures in the boundary layer can or may affect cell function. Critical to the entire essay are the methods used, or being developed, to monitor chemical profiles in the boundary layers. We review recent developments in ultramicro electrochemical sensors and tailored optical reporters suitable for the task in hand.
  • Article
    Modulation of extracellular proton fluxes from retinal horizontal cells of the catfish by depolarization and glutamate
    (Rockefeller University Press, 2007-07-30) Kreitzer, Matthew A. ; Collis, Leon P. ; Molina, Anthony J. A. ; Smith, Peter J. S. ; Malchow, Robert Paul
    Self-referencing H+-selective microelectrodes were used to measure extracellular proton fluxes from cone-driven horizontal cells isolated from the retina of the catfish (Ictalurus punctatus). The neurotransmitter glutamate induced an alkalinization of the area adjacent to the external face of the cell membrane. The effect of glutamate occurred regardless of whether the external solution was buffered with 1 mM HEPES, 3 mM phosphate, or 24 mM bicarbonate. The AMPA/kainate receptor agonist kainate and the NMDA receptor agonist N-methyl-D-aspartate both mimicked the effect of glutamate. The effect of kainate on proton flux was inhibited by the AMPA/kainate receptor blocker CNQX, and the effect of NMDA was abolished by the NMDA receptor antagonist DAP-5. Metabotropic glutamate receptor agonists produced no alteration in proton fluxes from horizontal cells. Depolarization of cells either by increasing extracellular potassium or directly by voltage clamp also produced an alkalinization adjacent to the cell membrane. The effects of depolarization on proton flux were blocked by 10 µM nifedipine, an inhibitor of L-type calcium channels. The plasmalemma Ca2+/H+ ATPase (PMCA) blocker 5(6)-carboxyeosin also significantly reduced proton flux modulation by glutamate. Our results are consistent with the hypothesis that glutamate-induced extracellular alkalinizations arise from activation of the PMCA pump following increased intracellular calcium entry into cells. This process might help to relieve suppression of photoreceptor neurotransmitter release that results from exocytosed protons from photoreceptor synaptic terminals. Our findings argue strongly against the hypothesis that protons released by horizontal cells act as the inhibitory feedback neurotransmitter that creates the surround portion of the receptive fields of retinal neurons.