True transmembrane potential curve from the surface of guinea pig ventricle: its relation to intrinsic deflection

¹ Department of Pharmacology, The University of British Columbia, Vancouver, British Columbia, Canada

The monophasic curves of the potential variations between an intracellular microelectrode and a remote reference electrode when recorded at sufficiently high speed show irregular upstrokes which are made up of a steep rise and one, or more, gentle rises; the relationships between these rises vary with position on the surface of the (guinea pig) ventricle. By subtracting, electronically, the local ECG obtained from a wire-loop electrode surrounding the microelectrode the irregularities can be removed: the subtractor output yields monophasic curves with even, sigmoid upstrokes. Such curves represent the true transmembrane potential. The use of the subtractor brings out the relationship between the intrinsic deflection of the local ECG and the upstroke of the transmembrane potential curve. Because these coincide and because the latter marks the influx of sodium ions into the cell, a direct relationship between the intrinsic deflection and the entry of sodium is revealed. This adds to the significance of the intrinsic deflection and permits a more rigorous definition of it.