Simplification and analysis of models of calcium dynamics based on IP3-sensitive calcium channel kinetics

Yuanhua Tang, John L. Stephenson, Hans G. Othmer

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Abstract

We study the models for calcium (Ca) dynamics developed in earlier studies, in each of which the key component is the kinetics of intracellular inositol-1,4,5-trisphosphate-sensitive Ca channels. After rapidly equilibrating steps are eliminated, the channel kinetics in these models are represented by a single differential equation that is linear in the state of the channel. In the reduced kinetic model, the graph of the steady-state fraction of conducting channels as a function of log10(Ca) is a bell-shaped curve. Dynamically, a step increase in inositol-1,4,5-trisphosphate induces an incremental increase in the fraction of conducting channels, whereas a step increase in Ca can either potentiate or inhibit channel activation, depending on the Ca level before and after the increase. The relationships among these models are discussed, and experimental tests to distinguish between them are given. Under certain conditions the models for intracellular calcium dynamics are reduced to the singular perturbed form εdx/dτ = f(x, y, p), dy/dτ = g(x, y, p). Phase-plane analysis is applied to a generic form of these simplified models to show how different types of Ca response, such as excitability, oscillations, and a sustained elevation of Ca, can arise. The generic model can also be used to study frequency encoding of hormonal stimuli, to determine the conditions for stable traveling Ca waves, and to understand the effect of channel properties on the wave speed.

Original languageEnglish (US)
Pages (from-to)246-263
Number of pages18
JournalBiophysical journal
Volume70
Issue number1
DOIs
StatePublished - Jan 1996

Bibliographical note

Funding Information:
This research is supported in part by NIH grant DK 31550 (to J. Stephen-son) and by NIH grant GM 29123 (to H. Othmer).

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