Comment on "Limit cycle oscillations in pacemaker cells"

In their paper (ibid., vol. 47, p. 1134-7, 2000) Endresen and Skarland have provided an interesting and welcome contribution to the area of mathematical modeling of cardiac action potentials by deriving a simple conservation principle based on the charge-voltage relationship of a capacitor and suggest that in cardiac pacemaker cell models "one should calculate the voltage using q=Cv, or one should at least select the initial conditions in accord with this equation." Their corresponding formulation relating cellular charge and potential is given by another algebraic equation. The problem with the conservation principle of this second equation however, is that only the intracellular surplus of K/sup +/, Ca/sup 2+/, and Na/sup +/ ions effectively contribute to transmembrane potential, an assumption which cannot be justified either biologically or numerically.