Volume 12 Supplement 1

Twentieth Annual Computational Neuroscience Meeting: CNS*2011

Open Access

Compensating the effect of dendritic diameters on calcium transients: a modeling study

BMC Neuroscience201112(Suppl 1):P60

DOI: 10.1186/1471-2202-12-S1-P60

Published: 18 July 2011

Intracellular Ca2+ does not only play a crucial role in the physiological interaction between the Ca2+ channels and Ca2+ activated K+ channels, it also serves as an important cellular messenger in signaling pathways. Therefore, accurate representation of intracellular calcium concentration is required in biophysically plausible models. Most commonly, intracellular calcium is modeled in morphologically realistic neuron models using single [13] or double exponential decaying pools [4] where Ca2+ concentration is computed in a submembrane shell only. These models are rather insensitive to the diameter of a compartment but fail to simulate interaction between Ca2+ channels and Ca2+ activated K channels occurring at multiple time scales. A more comprehensive and biophysically realistic solution is to use a detailed calcium dynamics model [5, 6] with buffers, pump and diffusion. When we used detailed Ca2+ dynamics model with a detailed morphology of a Purkinje cell, we discovered large gradients of Ca2+ levels in neighboring segments with different diameters even in the present of lateral diffusion. The peak Ca2+ concentration showed a close to linear inverse relationship to diameter of the compartment. We deem such pronounced gradients of Ca2+ as unphysiological and suggest that there should be a regulatory mechanism to compensate the effect of local dendritic geometry on buffered calcium transients.

In this study, we used a detailed calcium dynamics model [6] in a piece of dendrite where diameters of segments were varied to study different combinations of diameter changes (small to large variation). All the simulations were run using STEPS [7] with a fine resolution mesh to allow accurate modeling of diffusion.

Assuming a uniform calcium channel density for influx and uniformly distributed calcium buffers and pumps, difference in diameters of segments gave rise to large gradients of calcium transients. We investigated several possible mechanisms that could compensate the effect of local dendritic geometry on gradients of intracellular levels. These regulatory mechanisms included scaling of channel densities, scaling of pump densities, scaling of buffer concentrations and subcellular localization of buffers. Further, we also investigated combination of these regulatory mechanisms to compensate for the differences in peak amplitudes of calcium transients.

Our results suggest that the effect of local dendritic geometry on intracellular calcium levels can be partially compensated by each of the regulatory mechanisms investigated and can be sufficiently compensated by combination of those regulatory mechanisms. Therefore, on the basis of our modeling work, we propose a quantitative physiological investigation of the suggested mechanisms.

Authors’ Affiliations

(1)
Computational Neuroscience Unit, Okinawa Institute of Science and Technology
(2)
Theoretical Neurobiology, University of Antwerp

References

  1. De Schutter E, Bower JM: An active membrane model of the cerebellar Purkinje cell. I. Simulation of current clamps in slice. J Neurophysiol. 1994, 71: 375-400.PubMedGoogle Scholar
  2. Poirazi P, Brannon T, Mel BW: Arithmetic of subthreshold synaptic summation in a model CA1 pyramidal cell. Neuron. 2003, 37: 977-987. 10.1016/S0896-6273(03)00148-X.View ArticlePubMedGoogle Scholar
  3. Safiulina VF, Caiati MD, Sivakumaran S, Bisson G, Migliore M, Cherubini E: Control of GABA release at single mossy-fiber-CA3 connections in the developing hippocampus. Front Syn Neurosci. 2010, 2: 1.Google Scholar
  4. Tegnér J, Grillner S: Interactive effects of the GABABergic modulation of calcium channels and calcium-dependent potassium channels in lamprey. J Neurophysiol. 1999, 81: 1318-1329.PubMedGoogle Scholar
  5. Schmidt H, Stiefel KM, Racay P, Schwaller B, Eilers J: Mutational analysis of dendritic Ca2+ kinetics in rodent Purkinje cells: role of parvalbumin and calbindin D28k. J Physiol. 2003, 551: 13-32. 10.1113/jphysiol.2002.035824.PubMed CentralView ArticlePubMedGoogle Scholar
  6. Anwar H, Hong S, De Schutter E: Controlling Ca(2+)-Activated K (+) Channels with Models of Ca (2+) Buffering in Purkinje Cells. Cerebellum. 2010Google Scholar
  7. STEPS: [http://steps.sourceforge.net]

Copyright

© Anwar and De Schutter; licensee BioMed Central Ltd. 2011

This article is published under license to BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Advertisement