[Abstract Title]. - Society for Neuroscience

237. Synaptic Integration II
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 237.14/D39
Topic: B.07.c. Synaptic integration
Support: CIHR
Heart and Stroke Foundation of British Colubia and the Yukon
Canadian Stroke Network
Title: Pannexin-1 hemichannels open during low Mg2+-induced epileptiform bursting in the
hippocampus
Authors: *R. L. RUNGTA 1 , R. J. THOMPSON 1,2 , B. A. MACVICAR 1 ;
1 the Brain Res. Ctr., Univ. British Columbia, Vancouver, BC, Canada; 2 Dept. of Cell Biol. &
Anat., Univ. of Calgary, Calgary, AB, Canada
Abstract: Enhancing NMDA receptor activation by removing external Mg 2+ triggers
epileptiform Interictal spiking in hippocampal brain slices. In recent experiments we have found
that NMDA receptor activation can open pannexin-1 (Px1) hemichannels in hippocampal
neurons either acutely isolated or in brain slices. We hypothesized that by potentiating NMDAR
activity in hippocampal slices by perfusion of low Mg 2+ /5 mM K + bathing solution, Px1
hemichannels could open and contribute to the properties of interictal spiking. To show that Px1
channels open in low Mg 2+ /5 mM K + , we measured neuronal uptake of sulforhodamine 101
(SR101), which is normally excluded from neurons but can load when Px1 channels are opened.
We observed neuronal loading of SR101 in the CA1 region under low Mg 2+ /5 mM K +
conditions. Neuronal dye loading was blocked by pre-treatment with 50 κM APV (a NMDAR
antagonist) or by a short peptide sequence targeted against an extracellular domain of Px1
( 10 panx; 100 µM) which blocks Px1 hemichannels. To determine whether Pannexin-1 opening
could then affect seizure like activity, we monitored extracellular field potentials in both the CA1
and CA3 region. We confirmed that the initiation of low Mg 2+ -induced bursting was NMDARdependant
by blocking the induction of spontaneous bursting with 50 κM APV. In slices
displaying persistent CA1 bursting, perfusion of 10 panx reduced the interburst frequency by 28 ±
3 %, with recovery to 108 ± 4% (n=4 slices) of control upon washout of the peptide. Mean
amplitude of individual spikes was also reduced by 26 ± 10 %, with recovery to 87 ± 5 % of
control. This effect of 10 panx was not due to inhibition of the fast component of synaptic
currents, as 10 panx did not alter evoked field potentials in the presence of 2mM Mg 2+ . These data
support the hypothesis that pannexin-1 hemichannels can be opened by synaptic activation of
NMDARs, and may represent a novel target for intervention in epilepsy.
This work was supported by grants to BAM from the Canadian Institutes of Health Research and
the Heart and Stroke Foundation of British Columbia.