Effects of nanomolar concentration dihydroouabain on calcium current and intracellular calcium in guinea pig ventricular myocytes

A mathematical model of action potentials of mouse sinoatrial node cells with molecular bases

Genetically modified mice are popular experimental models for studying the molecular bases and mechanisms of cardiac arrhythmia. A postgenome challenge is to classify the functional roles of genes in cardiac function. To unveil the functional role of various genetic isoforms of ion channels in generating cardiac pacemaking action potentials (APs), a mathematical model for spontaneous APs of mouse sinoatrial node (SAN) cells was developed. The model takes into account the biophysical properties of membrane ionic currents and intracellular mechanisms contributing to spontaneous mouse SAN APs. The model was validated by its ability to reproduce the physiological exceptionally short APs and high pacing rates of mouse SAN cells. The functional roles of individual membrane currents were evaluated by blocking their coding channels. The roles of intracellular Ca²⁺-handling mechanisms on cardiac pacemaking were also investigated in the model. The robustness of model pacemaking behavior was evaluated by means of one- and two-parameter analyses in wide parameter value ranges. This model provides a predictive tool for cellular level outcomes of electrophysiological experiments. It forms the basis for future model development and further studies into complex pacemaking mechanisms as more quantitative experimental data become available.

Modulation of L-type calcium current in rat cardiac myocytes by sulfur dioxide derivatives

The effects of sulfur dioxide (SO(2)) derivatives (bisulfite and sulfite, 1:3M/M) on voltage-dependent L-type calcium current (I(Ca,L)) in isolated rat ventricular myocytes were studied using the whole cell patch-clamp technique. SO(2) derivatives increased I(Ca,L) in a concentration-dependent manner. SO(2) derivatives shifted both the steady-state activation and the inactivation curves of I(Ca,L) to more positive potentials, the effect on the latter being more pronounced. SO(2) derivatives markedly accelerated the recovery of I(Ca,L) from inactivation. SO(2) derivatives also significantly shortened the fast and slow time constants of inactivation. These results suggested that SO(2) inhalation might cause cardiac myocyte injury through increasing intracellular calcium via voltage-gated calcium channels.