Automated On-Line Determination of Membrane Responsiveness Curves

A system has been designed which provides automated on-line continuous plots of membrane responsiveness curves. The system is composed of amplifiers, positive peak-detecting and sample-and-hold circuitry, control logic, and display oscilloscopes. With an intracellular recording microelectrode impaled in a cardiac Purkinje fiber, the system acquires the membrane potential and maximum upstroke velocity of an action potential elicited from the resting or take-off potential. The resulting X-Y plot of varying membrane take-off potentials versus maximum upstroke velocity gives the "membrane responsiveness" relationship. This relationship reflects the relative availability of the depolarizing sodium system at different membrane potentials.