Plasma Membrane Ca²⁺ ATPase 2 Contributes to Short-Term Synapse Plasticity at the Parallel Fiber to Purkinje Neuron Synapse

Carboxyeosin, an inhibitor of PMCAs, enhanced PPF of PF-evoked EPSCs in PNs from WT but not PMCA2−/− mice. A, PPF of the PF input to a representative PN from a WT mouse, at varying ISIs, before (left) and after (middle) treatment with 10 μm CE. Note the increase in amplitude of the second and subsequent EPSCs compared with control. The far right panel shows the increase in the average PPR as a function of ISI for all WT cells, before (filled squares) and after treatment with CE (filled triangles) (n = 3). The lines represent double exponential fits to the mean data, and the dotted lines show extrapolated values determined from the exponential fits. CE also slowed the recovery of the PPF in WT cells. The first half-time for PPR decay, T1, in the WT cells increased from 25 to 41 ms, and the second, slower half-time for PPR decay, T2, increased from 102 to 204 ms in the presence of CE. CE application lasted 20 min. B, Results from the same experiment as in A, but from cells from PMCA2−/− mice, where the mean PPF (n = 3; far right) was not further enhanced by the presence of CE (open squares vs open triangles), nor its recovery slowed. The left and middle panels show traces from a representative PMCA2−/− cell. All values are means ± SEM.

Recovery of presynaptic PF [Ca²⁺]_i transients was slowed in slices from PMCA2−/− mice. A, PF stimulation-induced presynaptic Ca²⁺ transients. Top left, Transmission image. Asterisk denotes tip of stimulation electrode. GCL, Granule cell layer. Top right, Resting fluorescence image. Note two dye deposits and resting fluorescence of associated PF bundles. Bottom left, Pseudocolored map of peak ΔF/F signal, the baseline normalized change in fluorescence, induced by a single electrical stimulation of PFs. Bottom right, The time course of the Ca²⁺ transients extracted from regions of interest (white boxes, bottom left) along the PF bundle “beam”-shaped responsive area. Ca²⁺ signals are averages >20 stimulations. B, Time course of the average, normalized PF Ca²⁺ transient for WT (left, in black) and PMCA2−/− (right, in red). Each point represents the average response obtained from n = 6 slices normalized to their peak amplitude determined by double exponential fits (lines). C, Recovery time constants from double exponential fits. Values are mean ± SEM of the individual fast (T1) and slow (T2) time constants of recovery fitted individually to all PF presynaptic Ca²⁺ transients. **p < 0.01.