Modeling and Ion Mapping of Intracellular Calcium Distribution in Molluscan Neural Somata
Jung, Frank
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https://hdl.handle.net/2142/70706
Description
Title
Modeling and Ion Mapping of Intracellular Calcium Distribution in Molluscan Neural Somata
Author(s)
Jung, Frank
Issue Date
1983
Department of Study
Physiology and Biophysics
Discipline
Biophysics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biophysics, General
Abstract
To understand the mechanism of rapid (time constants of 1-3 sec) buffering of intracellular calcium in molluscan cell bodies, a diffusion-reaction model was developed. The model took into account the binding reactions of Ca('2+) with a calcium-indicating dye (arsenazo III) and an endogenous Ca('2+) buffer. The results from this model show that intracellular calcium can be buffered rapidly and dominantly by an endogenous buffer independent of mitochondrial Ca('2+) uptake and calcium pumps. During stimulation of the model cell, the submembrane calcium ion concentration can reach more than 1,000 times the steady-state value. Futhermore, Ca('2+) is restricted to within a few microns from the cell plasma membrane as it diffuses intracellularly. The accumulation of high concentration of Ca('2+) at the submembrane region can explain a number of properties of membrane calcium current I(,Ca) in molluscan neurons: (i) Decay kinetics of I(,Ca) during a voltage clamp depolarization period; (ii) I(,Ca)-Voltage relation; (iii) I(,Ca) as a function of intracellular calcium ion concentration; (iv) I(,Ca) as a function of extracellular calcium ion concentration. To understand the morphological bases of this model, I used electron microscopy and ion microscopy to probe the structure of the neurons in the mollusc Archidoris montereyensis. Electron microscopy showed that calcium-containing granules (lipochondria) exist in large numbers at the plasmalemma of these neurons. Ion images of the neurons processed by freeze-substitution showed that the nucleus consistently contains less calcium than the cytoplasm. These results suggest that in these neurons, the calcium buffering capacity of the cytoplasm is greater than that of the nucleus.
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