FIG. 2.
Endocytosis, recovery from paired-pulse depression, and the L-type calcium current I–V relationship are the same during nighttime and daytime recordings in nystatin perforated-patch. A: endocytosis recorded from 1 nighttime (black, 1:47 AM, resting Cm = 3.02 pF) and 1 daytime (red, 1:18 PM, resting Cm = 3.75 pF) terminal after successive 200-ms depolarizations from −60 to 0 mV. B: average kinetics of endocytosis after 200-ms depolarizations were the same during the day- and nighttime. Endocytosis traces were fit with double exponentials (day: τfast = 2.0 ± 0.3 s, 52% of ΔCm, τslow = 18.6 ± 2.8 s, n = 17; night: τfast = 1.4 ± 0.1 s, 51% of ΔCm, τslow = 15.7 ± 2.1 s, n = 9). The kinetics of endocytosis were also the same during the day- and nighttime for 2- and 20-ms depolarizations (not shown, 2-ms endocytosis: day: τfast = 1.1 ± 0.4 s, 32% of ΔCm, τslow = 15.3 ± 2.5 s, n = 4; night: τfast = 1.3 ± 0.3 s, 26% of ΔCm, τslow = 15.1 ± 4.8 s, n = 5; 20-ms endocytosis: day: τfast = 1.5 ± 0.4 s, 34% of ΔCm, τslow = 21.6 ± 4.2 s, n = 5; night: τfast = 1.8 ± 0.3 s, 38% of ΔCm, τslow = 26.6 ± 5.9 s, n = 5). Error bars represent SE. C: recovery from paired-pulse depression was measured for several interpulse intervals (interpulse interval, number of cells day/night: 50 ms, 6/5; 100 ms, 8/7; 250 ms, 7/6; 500 ms, 9/7; 1 s, 9/7; 3 s, 9/4; 5 s, 9/6; 7 s, 8/2; 10 s, 8/5; 15 s, 7/6). Although the curves diverge at the 15-s interpulse interval, there is no statistical difference between those night and day points (P = 0.06). Both curves are double exponential (day: τfast = 359 ms, 67% of recovery, τslow = 2.9 s; night: τfast = 421 ms, 64% of recovery, τslow = 7.0 s). D: typical example of paired-pulse depression from this synapse at night (2:10 a.m.) and the averaged L-type calcium current I–V relationships for night- and daytime recordings. Note that both the daytime and nighttime averaged I–V curves peak near 0 mV.