Figure 4.

Effects of the SERCA Ca²⁺-pump inhibitor thapsigargin on voltage-dependent enhancement of transmitter release. (a) mEPSPs induced by 0.5 M sucrose (Left) or 0.5 M sucrose plus a presynaptic tetanic stimulation at 100 Hz for 4 s (Right). At t = 0, thapsigargin was drop-applied into the Krebs bathing solution containing 0 mM Ca²⁺ and 10 mM Mg²⁺, producing a concentration of 2 μM. mEPSPs from one representative experiment recorded 5 and 4 min before injection and 5, 6, 25, and 26 min after bath application are illustrated. (b) Difference between normalized average integral values of the mEPSPs with and without presynaptic action potentials, 400 pulses at 100 Hz, is plotted from nine experiments like the one illustrated in a.