Fig. 5. (A) Action potentials recorded in sweeps of 12.75 ms duration. The initial 2.5 ms of each sweep were defined as baseline and used to measure the transepithelial potential. The baseline was then adjusted to 0 mV. One large (red line) and one small (blue line) action potential are highlighted. The peak-to-peak (p-p) amplitudes of each action potential occurring over a 10 min period were measured and plotted versus time (B). The amplitude reduction during bursts then became obvious (arrowheads). The massive bursting activity of the cell firing the small action potentials (solid arrowhead) gives rise to a third peak when the data are presented as an amplitude histogram (C), generating a false third action potential class (arrowhead). Both types of plot were analyzed to determine the threshold for action potential sorting (dashed lines).