Figure 4. Multivesicular release was sensitive to small hyperpolarizing steps.

(A) Example trace showing that multivesicular I_A(glu) release events paused for several seconds immediately after hyperpolarizing the rod from −40 to −43.5 mV and the overall rate of these events remained slower for the remainder of the step. Red triangle denotes the time interval measured and plotted as red triangles in panel B. (B) Frequency distribution of intervals between multivesicular events measured at −40 and −43.5 mV (n = 9 rods), each fit with a single Gaussian (−40 mV, 1583 ± 1004 ms; −43.5 mV, 2896 ± 1872 ms). Hyperpolarization from −40 (279 events) to −43.5 (129 events) significantly extended the mean interval between multivesicular events (p<0.0001, unpaired t-test). Filled circles, stars and triangles show the intervals measured in individual trials immediately after hyperpolarizing steps of 1 (n = 7), 2 (n = 7), or 3.5 mV (n = 16) from a prior holding potential of −40 mV, respectively. All of these intervals were >1 standard deviation (vertical dotted lines) above the mean interval between multivesicular events measured at −40 mV.