SCIENTIFIC ORGANIZATION:
Saint-Petersburg State Polytechnic University, Laboratory of Molecular Neurodegeneration

REPORT FORM:
«Poster report»

AUTHOR(S)
OF THE REPORT:
Egorova Polina, Bezprozvanny Ilya

TALKING POINTS:

In the brain are expressed a few subtypes of small conductance calcium-activated potassium channels (SK channels) [1] with the SK2 isoform predominant in Purkinje cells (PCs) [2, 3]. Thus, the SK2 channel subtype is the most attractive pharmacological target for treatment of cerebellar ataxia. Indeed, in previously studies we have directly demonstrated that SK2 channels control normal PC pacemaking. We have also demonstrated that application of the SK/IK modulator NS309 and the SK3/SK2 modulator CyPPA restore regular pacemaker activity means tonic firing pattern of bursting cerebellar PCs from transgenic mice with spinocerebellar ataxia type 2 (SCA2) and also exert beneficial effect in SCA2 mice [4]. However for a start pre-clinical electrophysiological trials in vivo should be carried out.

In our preliminary studies it was shown that selective positive modulators of SK channels bound signal of PC cells in vivo in laboratory mice. Experimental technique of extracellular recordings of PC cell activity patterns in vivo was adapted from [5]. The differentiating factor of PC signal in the case of extracellular recording in vivo is complex spike. Complex spikes are caused by climbing fiber activation and can involve the generation of calcium-mediated action potentials in the dendrites whereas simple spikes are activated synaptically by the parallel fibers, the axons of the granule cells [6, 7].

Based on experimental data obtained via extracellular PC signal registration in vivo we can conclude that selective positive modulators of SK channels effect on PC cells activity on intact animals in principle. Also there is an evidence that the application of 1 mM CyPPA decreases firing frequency of 26 per cent for one hour and the application of 0,1 mM NS309 decreases firing frequency of 47 per cent for one hour.

Further to these initial experiments with a view to modulate real drug delivery fashion the effect of modulators on PC firing rate in the case of intravenous injection was tested. PC signal from 6 months old WT mouse before and after injection was recorded. The first half hour after CyPPA injection PC signal was bursting, in 30 min after application the signal was reverted to tonic pattern. In addition to this the firing frequency of PC signal in one hour after injection diminished about twice as low and in hour and a half diminished in three times. So that we can conclude that this manner of drug delivery can be used in following pre-clinical investigations and also clinical trials because CyPPA molecules can cross the blood brain barrier and effect on firing rate of PC cells. We will expand these experiments on SCA2 mice model. Our latest results on this project will be presented.

References:

1. Adelman, J.P., J. Maylie, and P. Sah, Small-conductance Ca2+-activated K+ channels: form and function. Annu Rev Physiol, 2012. 74: p. 245-69.
   
   
2. Cingolani, L.A., et al., Developmental regulation of small-conductance Ca2+-activated K+ channel expression and function in rat Purkinje neurons. J Neurosci, 2002. 22(11): p. 4456-67.
   
   
3. Hosy, E., et al., SK2 channel expression and function in cerebellar Purkinje cells. J Physiol, 2011. 589(Pt 14): p. 3433-40.
   
   
4. Kasumu, A.W., et al., Selective positive modulator of calcium-activated potassium channels exerts beneficial effects in a mouse model of spinocerebellar ataxia type 2. Chem Biol, 2012. 19(10): p. 1340-53.
   
   
5. Gao, Z., et al., Cerebellar ataxia by enhanced Ca(V)2.1 currents is alleviated by Ca2+-dependent K+-channel activators in Cacna1a(S218L) mutant mice. J Neurosci, 2012. 32(44): p. 15533-46.
   
   
6. Raman, I.M. and B.P. Bean, Ionic currents underlying spontaneous action potentials in isolated cerebellar Purkinje neurons. J Neurosci, 1999. 19(5): p. 1663-74.
   
   
7. Ito, M., Cerebellar long-term depression: characterization, signal transduction, and functional roles. Physiol Rev, 2001. 81(3): p. 1143-95.