Prof. George Lykotrafitis (University of Connecticut)

Particle-based modeling of the axon and single molecule AFM experiments on SK channels in pyramidal neurons
When Mar 17, 2017
from 02:00 PM to 03:00 PM
Where LR8
Contact Name
Contact Phone 01865-283302
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It has been recently demonstrated via super-resolution microscopy that unlike in the soma and dendrites, the axon membrane skeleton comprises a series of actin rings at a periodic distance of 180 nm to 190 nm. These rings are connected by extended spectrin filaments. In addition, we have recently shown, by using atomic force microscopy, that the stiffness of the axon plasma membrane is significantly higher than the stiffness of somatic and dendritic plasma membranes. Based on these findings and using our in-house developed Interactive MultiPhysics Environment for Unified Simulations (IMPETUS), we developed a coarse-grain molecular dynamics model of the axon membrane skeleton to investigate its biomechanical behavior. The proposed model validates the stiffness of the axon membrane by comparing the median value of its Young’s modulus to the result determined by atomic force microscopy. We expect that the model can be used to study the mechanical stability of the axon.

Small-conductance calcium-activated potassium (SK) channels are a family of potassium channels that reside primarily in neuronal dendrites and are involved in long-term potentiation, and learning and memory. In contrast, the expression of SK channels on the soma is much lower. However, it remains unclear if SK channels are present on axonal membranes. To test whether SK channels are localized on axons, we employed single molecule atomic force microscopy (AFM) combined with natural toxins. AFM tip functionalized with apamin, a selective SK channel blocker, was used to detect the SK channels in living neurons by measuring the unbinding forces between apamin and SK channels.  When 1µm2 scan areas were probed along the axon, we observed mean unbinding forces of 20±8.0pN in about 5.6% of the sampled sites (n=6). However, when we repeated the experiment on cells pretreated with apamin, we observed a significant decrease in the frequency in the unbinding forces (0.58%, n=3). We also found that axonal SK channels are regulated by cAMP activated protein kinase A (PKA), as with SK channels present in other neuronal compartments. Therefore, we show that apamin-sensitive SK channels reside on the axon initial segment and are under the control of tonic cAMP-PKA.