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Regulation of local calcium transients in the Purkinje cell dendritic tree mediated by potassium channel

Regulation of local calcium transients in the Purkinje cell dendritic tree mediated by potassium channel

Society for Neuroscience Abstract Viewer & Itinerary Planner : Abstract No 366 1

At the parallel fiber-Purkinje cell synapse, postsynaptic long term depression (LTD) and long term potentiation (LTP) can account for the modulation of the synaptic weights. The striking finding is that induction protocols are the same except that the depression requires a transient increase in the calcium concentration in the dendritic tree mediated by the climbing fiber input, the second excitatory input on the Purkinje cell, and parallel fiber-induced mGluR1 receptor activation. Thus calcium elevation in the dendritic tree appears to be one of the key feature of the regulation of the synaptic weights.As the Purkinje cell dendritic tree contain a variety of voltage-dependent calcium and potassium channels that can influence the dendritic integration and the subsequent plasticity at the parallel fiber-Purkinje cell synapse, we set out to study the influence of the potassium channels on the shape and the amplitude of calcium transients. Using patch-clamp recordings in acute cerebellar slices and two-photon laser scanning microscopy, we monitor fast calcium transients in the Purkinje cell dendritic tree induced by synaptic stimulation of parallel and climbing fibers. We first show that application of 4-AP, a blocker of A-type current, allows the propagation toward the soma of dendritic calcium spikes induced by synaptic stimulation. In some cases, spontaneous dendritic calcium spikes can be observed under 4-AP, suggesting the involvement of low-threshold voltage dependant calcium channels. We also show that 4-AP application (100 microM) increases the size of the subthreshold calcium transient induced by parallel fiber stimulation and the size of the calcium spike induced by the climbing fiber. These results and the fact that A-type channels can be regulated by PKA and PKC strongly suggest that potassium channels may be involved in the regulation of dendritic integration mediated by calcium.

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