The electrophysiological basis of MAP recordings.

by gest on N ovem er 8, 2016 D ow nladed fom Recently, differing views as to the genesis of monophasic action potential (MAP) recordings have surfaced [1–3]. Kondo et al. [1,3] claim that MAP recordings come about because core conductor theory dictates that the extracellular potential is a scaled version of the transmembrane voltage and that the contact electrode acts as a stationary ground. Franz [2] holds to the view that injury currents at the boundary of the contact electrode zone of influence lead to extracellular potential changes which reflect changes in transmembrane voltage. As a consequence of these divergent views, the importance of one electrode with respect to the other has come into question. MAP electrodes are similar to potentials recorded with the sucrose gap technique [4]. That is, the technique functions as MAP recordings do, indirectly measuring transmembrane voltage by differencing extracellular potentials. Due to its relative simplicity, this technique warrants further consideration to determine if similar physics concepts are at work, which may shed light on the present issue. The sucrose gap technique separates two portions of an active cable with a perfusion of sucrose solution that serves to stop propagation of any activity across the gap due to the high resistivity of the sucrose region. The intracellular domains are still connected. By taking the difference in extracellular potentials on opposite sides of the sucrose gap, an approximation of the transmembrane voltage is obtained. The sucrose gap works because the intracellular domains are well connected. Potential theory states that the voltage between two points is independent of the path traveled between the points. Thus, to find the voltage between the two extracellular points, we may follow a purely extracellular path or follow a path that crosses the membrane, travels intracellularly, and then crosses the membrane back