Curvature Dependence of Propagating Velocity for a Simplified Calcium Model

It is known that curvature relation plays a key role in the propagation of two-dimensional waves in an excitable model. Such a relation is believed to obey the eikonal equation for typical excitable models (e.g., the FitzHugh-Nagumo (FHN) model), which states that the relation between the normal velocity and the local curvature is approximately linear. In this paper, we show that for a simplified model of intracellular calcium dynamics, although its temporal dynamics can be investigated by analogy with the FHN model, the curvature relation does not obey the eikonal equation. Further, the inconsistency with the eikonal equation for the calcium model is because of the dispersion relation between wave speed s and volume-ratio parameter γ in the closed-cell version of the model, not because of the separation of the fast and the slow variables as in the FHN model. Hence this simplified calcium model may be an unexpected excitable system, whose wave propagation properties cannot be always understood by analogy with the FHN model. School of Computing and Mathematical Sciences, Auckland University of Technology, Private Bag 92006, Auckland 1142, New Zealand. Phone: +64-9-9219999-x5094; Email address: [email protected]). Department of Mathematics, National Chung Cheng University, 168, University Road, Min-Hsiung, Chia-Yi 621, Taiwan. (Email address: [email protected]). To whom the correspondence should be addressed (J.-C. Tsai). Department of Mathematics, University of Auckland, Private Bag 92019, Auckland, New Zealand (Email address: [email protected]).