Electrical interactions between cardiac cells: what can we learn from two-cell systems?

With the ability to enzymatically isolate single cardiac cells from mammalian hearts, the research in cardiac electrophysiology has become focused on the study of cardiac electrical properties at the cellular level. Such research yields important information on individual membrane ionic currents and their relation to the single cell action potential. However, it is often difficult to predict how (changes in) individual currents affect cell-to-cell transfer of the cardiac action potential. Therefore, Joyner and coworkers introduced the "coupling clamp" technique in which an isolated cardiac cell can be electrically coupled to either another isolated cardiac cell or to an analog model cell that mimics cardiac cell properties (RC circuit). Building on this concept, we developed the PC-controlled "model clamp" technique, in which an isolated cardiac cell is dynamically coupled to a comprehensive model cell that is being computed in real time. With this system we have the ability to vary the intercellular coupling conductance as well as the intrinsic cellular properties of the model cell. For (under)graduate students, the coupling clamp and model clamp systems may prove useful tools to learn understand the electrical interactions between cardiac cells underlying synchronization of pacemaker cells and discontinuous action potential conduction between ventricular cells.