Model clamp: a computer tool to probe action potential transfer between cardiac cells

In the early nineties, 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 (RC circuit). In brief, an amplifier system does a continuous analog computation of the current that would be flowing between the two cells if there had been an intercellular coupling conductance G_c, and then provides current inputs to the cells accordingly. Building on this concept, we developed the computer-controlled "model clamp" technique, in which an isolated cardiac cell is dynamically coupled in real time to a comprehensive mathematical cell model (e.g., the phase-2 Luo-Rudy model). With this system we have the ability to vary coupling conductance, effective size of both model cell and real cell, and intrinsic cellular properties of the model cell. In courses on cardiac electrophysiology, the model clamp system provides a useful computer tool to probe action potential transfer between cardiac cells. It can be used to assess alterations in the critical value of coupling conductance required for action potential transfer from a real ventricular cell to the Luo-Rudy model ventricular cell upon exposure of the real cell to, e.g., noradrenaline.