"CONCENTRATION DRIFT AND RATE-DEPENDENT RESTITUTION
IN THE CRN ATRIAL MEMBRANE MODEL"
Robert Oliver and Wanda Krassowska (Department of Biomedical
Engineering and Center for Nonlinear and Complex Systems, Duke University,
Durham, NC)
Abstract
In this presentation we will discuss ionic concentration drift and rate-dependent
restitution in an atrial
membrane model. The human atrial membrane model developed by Courtemanche
et al. is balanced so
intracellular ionic concentrations equilibrate at rest. However, [Na]i,
[K]i, and action potential duration (APD)
drift slowly during pacing. We find that modifying the model by holding
[Na]i and [K]i constant eliminates APD
drift. Using S1-S2, steady-state, and dynamic pacing protocols, the
effect of APD drift on APD restitution is
investigated in a membrane patch having either no drift (constant concentrations)
or drift (variable
concentrations) CRN membrane dynamics. We find that with no drift APD
restitution varies only marginally with
pacing protocol whereas with drift it varies markedly. These results
show pacing protocol and concentration
drift can have a significant effect on APD restitution. In addition,
concentration drift could have a significant
effect on long-term membrane dynamics and must be considered during
pacing studies of cardiac dynamics.