Bufadienolides and ouabain enhanced the firing activity of MCs in a concentration-dependent manner.

<p><b>A</b> Original recording from a representative MC illustrated the increase in firing rate and depolarization following application of cinobufagin at 1 µM and 5 µM, respectively. <b>B1</b> Concentration-response curves for spiking of MCs evoked by various concentrations of bufadienolides and ouabain. The firing rates in the presence of bufadienolides and ouabain were normalized with respect to the control condition and were averaged (each point was the mean ± SEM of 3 to 7 cells). Error bars have been left out for clarity. The lines are fits for each set of data to the Hill equation: <i>y</i> = <i>Axⁿ</i>/(<i>K</i>_d<i>ⁿ</i> + <i>xⁿ</i>), where <i>y</i> is the increase of spiking rate, <i>A</i> is the maximal increase, <i>K</i>_d is the apparent dissociation constant for bufadienolides, and <i>n</i> is the Hill coefficient. <i>K</i>_d and <i>A</i> were estimated using a Marquardt nonlinear least squares routine. <b>B2</b> Relationship between concentrations of bufadienolides or ouabain and evoked depolarization of membrane potential. Error bars were left out for clarity.