Activity-Dependent Change in AMPA Receptor Properties in Cerebellar Stellate Cells

Rectification properties of kainate-evoked currents in outside-out patches excised from the soma of stellate cells. A, Outwardly rectifying I–Vrelationship of kainate-evoked currents in an outside-out patch from a control cell. Spermine (100 μm) was included in the pipette solution. B, The agonist-evoked current in an outside-out patch excised from a TTX-treated stellate cell exhibited an inwardly rectifying I–V relationship. The slice was treated with 1 μm TTX for >2 hr and subsequently washed before the recording. C, Histogram of the rectification index of kainate-evoked currents in outside-out patches from control cells (defined as the ratio of current amplitude at +40 mV vs the predicted linear value at +40 mV). The rectification index was 1.1 ± 0.1 (n = 26 patches). D, Histogram of the rectification index of agonist-evoked currents in outside-out patches from TTX-treated cells (n = 8 patches) and cells treated with ω-conotoxin (ω-CTX) (500 nm ω-conotoxin GVIA for >2 hr before recording; n = 7 patches). A current trace was shown in our previous publication (Liu and Cull-Candy, 2000).

High Ca²⁺ permeability of AMPARs in outside-out patches from TTX-treated cells. TheI–V relationships of agonist-evoked currents in an outside-out patch were measured in Na⁺-rich solution and in Ca²⁺-rich solution. The reversal potentials of these currents, V_revNa andV_revCa, were determined from theirI–V plots. A, I–Vrelationship of a response from an outside-out patch from control cells. The currents reversed at a more hyperpolarized potential in Ca²⁺-rich solution (30 mmCaCl₂; dashed line) than in Na⁺-rich solution (135 mm NaCl;solid line), indicating a lower permeability to Ca²⁺ than to Na⁺.Bottom, The same I–V relationship as shown at the top, but on an expanded scale. Spermine was not included in the pipette solution. B,I–V relationship of a response from a patch from TTX-treated cells. The reversal potential of the agonist-evoked current in Ca²⁺-rich solution is close to the reversal potential in Na⁺-rich solution. C, The Ca²⁺ permeability of AMPARs in outside-out patches from control cells (n = 4) was significantly lower than that from TTX-treated cells (n = 5; p < 0.04). The Ca²⁺ permeability, P_Ca/P_Na, was calculated from the reversal potentials in Na⁺-rich and Ca²⁺-rich solutions (as described in Materials and Methods).

EPSCs mediated by GluR2-containing and by GluR2-lacking AMPARs have similar kinetic properties. A, At −60 mV, EPSCs were mediated by a mixed population of AMPARs; the 10–90% rise time was 0.20 msec. The decay time course (fitted with the single exponential function) gave a time constant of 0.86 msec. At +40 mV, EPSCs were mediated by GluR2-containing AMPARs. The 10–90% rise time of the synaptic current was 0.18 msec. The decay time course was best fitted with the two exponential functions. The fast component (96% of peak amplitude) had a decay time constant of 0.81 msec; the slow component was 3.28 msec. The weighted decay time constant was 0.90 msec. B, Synaptic currents at −60 and +40 mV normalized to their peak current amplitude to allow comparison of decay time. In this example, the decay time was marginally slower at +40 mV.C, The decay time constant of synaptic currents at −60 mV was not significantly different from that at +40 mV (p = 0.12 by paired t test;n = 14 cells). Open circles andopen triangles are individual data, and filled circle and filled triangle are average values ± SE. D, Summary of the 10–90% rise time of synaptic currents at −60 and +40 mV (p = 0.37 by paired t test;n = 14 cells).