The CA_v2.1/α1A (P/Q-type) voltage-dependent calcium channel mediates inhibitory neurotransmission onto mouse cerebellar Purkinje cells

The effects of voltage-dependent calcium channel (VDCC) antagonists on spontaneous inhibitory postsynaptic currents (sIPSCs) in mouse Purkinje cells were examined using in vitro cerebellar slices. The inorganic ion Cd ²⁺ reduced sIPSC amplitude and frequency. No additional block was seen with the Na ⁺ channel antagonist tetrodotoxin (TTX) suggesting that all action potential-evoked inhibitory GABA release was mediated by high-voltage-activated VDCCs. No evidence was found for involvement of Ca _v 1/α1C and α1D (L-type), Ca _v 2.2/α1B (N-type) or Ca _v 2.3/α1E (R-type) high-voltage-activated VDCCs or low-voltage-activated Ca _v 3/α1G, α1H and α1I (T-type) VDCCs in mediating presynaptic GABA release. Blockade of sIPSCs by 200 nmω-agatoxin IVA implicated the Ca _v 2.1/α1A (P/Q-type) subtype of high-voltage-activated VDCCs in mediating inhibitory transmission. Inhibition by ω-agatoxin IVA was similar to that seen with Cd ²⁺ and TTX. Selective antibodies directed against the Ca _v 2.1 subunit revealed staining in regions closely opposed to Purkinje cell somata. Ca _v 2.1 staining was colocalized with staining for antibodies against glutamic acid decarboxylase and corresponded well with the pericellular network formed by GABAergic basket cell interneurons. Antibody labelling of Ca _v 2.3 revealed a region-specific expression. In the cerebellar cortex anterior lobe, Ca _v 2.3 staining was predominantly somatodendritic; whilst in the posterior lobe, perisomatic staining was seen primarily. However, electrophysiological data was not consistent with a role for the Ca _v 2.3 subunit in mediating presynaptic GABA release. No consistent staining was seen for other Ca _v (α1) subunits. Electrophysiological and immunostaining data support a predominant role for Ca _v 2.1 subunits in mediating action potential-evoked inhibitory GABA release onto mouse Purkinje cells.