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. 2007 Jul 30;178(3):489–502. doi: 10.1083/jcb.200702072

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Copyright © 2007, The Rockefeller University Press

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Figure 7. — Ca_vβ subunit–specific determination of facilitation and depression in autaptic hippocampal neurons. (A and B) EPSC recordings of autaptic hippocampal neurons exogenously expressing Ca_vβ_2a and Ca_vβ_4b subunits in 4 mM Ca²⁺. (A) Representative autaptic EPSC traces from noninfected and Ca_vβ_2a and Ca_vβ_4b subunit–infected neurons reveal that in the presence of Ca_vβ_2a and Ca_vβ_4b subunits, synaptic depression is increased during long 20-Hz stimulations. Gray areas represent the asynchronous release. (B) Bar graph of the quantified EPSC ratios of Ca_vβ_2a and Ca_vβ_4b subunit–infected and noninfected neurons. The EPSC amplitudes of the first and second EPSC (top), the first and the mean from the 27–30th EPSC (middle), and the largest EPSC during a train and the mean from the 27–30th EPSC (bottom). (C) Relative EPSCs for Ca_vβ_2a- and Ca_vβ_4b-infected and noninfected neurons. The EPSC amplitudes during the 20-Hz pulse train were related to the EPSC elicited by the first pulse. The decline in EPSC amplitude could be fitted with a single exponential starting from the largest EPSC within the pulse train. (D) Bar graph of the mean maximal EPSC amplitude of Ca_vβ_2a and Ca_vβ_4b subunit–infected and noninfected neurons during a 20-Hz pulse train. (E and F) Comparison of the RRP before and after 30 2-ms-long pulses to 10 mV (20-Hz stimulation). (E) Example traces of sucrose responses before (P2) and after the 20-Hz stimulation (P1). (F) Relative pool size for Ca_vβ_2a- and Ca_vβ_4b-infected and noninfected neurons. The relative pool size was determined by the ratio between the sucrose response after the 20-Hz stimulation (P1) and the sucrose response before the stimulation (P2). (G) Time course of asynchronous release during a 20-Hz pulse train. The charge of the largest EPSC (EPSC_max) within the 20-Hz train was compared with the charge of the asynchronous release for each EPSC. (H) Bar graph of the quantified total charge during a 20-Hz stimulation protocol for the phasic release and asynchronous release for Ca_vβ_2a- and Ca_vβ_4b-infected and noninfected neurons. The mean values of the time course of depression (C) and the asynchronous release (G) were fitted with a single exponential, and the time constants for each fit and the number of experiments (given in parentheses) are given in the diagrams. Error bars represent SEM. * P, < 0.05; **, P < 0.01.