Structure Dependence of the Calcium Dynamics in Purkinje Neuron Dendrites during Generation of Bursting Discharges: a Simulation Study |
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Authors: | T S Novorodovskaya I B Kulagina |
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Institution: | 1.Oles’ Gonchar Dnepropetrovsk National University,Dnipropetrovsk,Ukraine |
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Abstract: | In the model of a cerebellar Purkinje neuron with reconstructed active dendrites, we investigated the impact of the ratio
between volumes of the endoplasmic reticulum (organellar calcium store) and cytosol on the Ca2+ dynamics in asymmetrical parts of the dendritic arborization during generation of different structure-dependent patterns
of bursting activity. Tonic synaptic excitation homogeneously distributed over the dendrites (a spatially homogeneous stationary
input signal) caused spatially heterogeneous variations of the dendritic membrane potential (MP) accompanied by periodical
or nonperiodical bursts of action potentials at the cell output. The MP waveforms recorded from the segments of asymmetrical
dendrites were then applied to the membrane of selected dendrite segments as command voltages in a dynamic clamp mode. In
these segments, the relative size of the stores was varied. This provided equal to each other local calcium currents and influxes
into the cytosol of the segment differently filled with the organellar store. Regardless of the impulse pattern, microgeometry
of the segment and the store modulated calcium transients exactly in the same way as in previous studies of electrical and
concentration responses to local phasic synaptic excitation of the modeled neuron. Peak values of depolarization-induced elevations
of the cytosolic Ca2+ concentration increased with the portion of the intracellular volume occupied by the store. The most important factor defining
this dependence was the ratio of the membrane area vs the organelle-free cytosol volume of the dendritic segment. Concentrations of Са2+ deposited in equal-sized segments of asymmetrical parts of the dendritic arborization where asynchronous unequal variations
of the MP were observed during generation of nonperiodical bursting at the output demonstrated considerable specificity. A
greater amount of calcium was deposited in the segments staying, on average, in a high-depolarization state for a longer time
(this intensified activation of calcium channels and amplified the corresponding Ca2+ influx into the cytosol). Hence, local dynamics of the Ca2+ concentration depend directly on local microgeometry and indirectly on global macrogeometry of the dendrite arborization,
as the latter determines spatial asymmetry-related unequal transients in different parts of the dendritic arborization having
active membrane properties. |
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