Can the light-addressable potentiometric sensor (LAPS) detect extracellular potentials of cardiac myocytes?

The light-addressable potentiometric sensor (LAPS) measures localized photo -induced currents from a silicon wafer, which are dependent on the local su rface potential and on the intensity of the light pointer. In this study th e ability of the LAPS to record extracellular potentials of adherent cells was investigated. Time dependent LAPS photocurrent signals that correlated in time with contractions were recorded from beating cardiac myocytes cultu red on LAPS surfaces. Signals could be recorded both when the LAPS was bias ed to working points where the photocurrent was maximally sensitive to pote ntial changes and when it was biased to working points where the photocurre nt was insensitive to changes in surface potential. Therefore, signals coul d not be predominantly created by changes in extracellular potential and mi ght be related to mechanical contractions. One possible explanation might b e, that the cell-induced modulation of photocurrents arose as a result of c ell shape changes. Such alterations in cell shape might have focused and de focused the light pointer and, thus, modulated its intensity. To further te st this hypothesis, height changes of beating cardiac myocytes were measure d with an atomic force microscope (AFM). They were found to match well with signals derived from LAPS measurements. Therefore, it can be concluded, th at LAPS signals were mainly determined by the periodic changes in shape of beating heart cells, and this interference precludes the measurements of ex tracellular electrophysiological potentials from these cells.