Fig. 4.
Complex effects on depression with reduced [Ca2+]o and/or increased [Mg2+]o (ΔCa/Mg). A, Sample records from two cells, illustrating diverse effects of 1 Ca/2 Mg solution. In both cells 1 Ca/2 Mg reduced initial EPSCs, but depression in cell 1 was unchanged while depression incell 2 was reduced. Averages of four to nine traces displayed. B, Average effects of three different solutions. Control QEPSC responses were normalized by first response in control for each cell and averaged across cells (solid squares). Each ΔCa/Mg QEPSCwas normalized by first response in ΔCa/Mg before averaging across cells (open triangles). Inhib. refers to the average decrease in size of QEPSC after first stimuli in ΔCa/Mg compared with control. C, D, Multiple regression analysis of relative change in paired-pulse depression (relative ΔPPD) correlated with two factors:QEPSC size in ΔCa/Mg relative to control (S1ΔCa/Mg/S1control), and paired-pulse plasticity in control (S2control/S1control). Relative ΔPPD = (PPD in ΔCa/Mg − PPD in control)/PPD in control, where PPD = (S1 − S2)/S1. Data pooled across 31 cells in various ΔCa/Mg solutions; each symbol represents data from one cell, averaged over 5–20 sweeps. Partial correlation coefficients are denoted by r2 values. C, Scatter plot of relative ΔPPD versus initialQEPSC in ΔCa/Mg, normalized by initialQEPSC in control (S1ΔCa/Mg/S1control). There was no significant correlation (solid line) when both factors were considered. D, Scatter plot of relative ΔPPD versus paired-pulse plasticity in control (S2control/S1control). A significant correlation (solid line) was present even when both factors were considered; in cells with strongest baseline depression (S2control/S1control small), the depression was least affected by ΔCa/Mg.