Activation of P₂-purino-,α₁-adreno and H₁-histamine receptors triggers cytoplasmic calcium signalling in cerebellar purkinje neurons

The cytoplasmic calcium concentration ([Ca²⁺]_i) was measured from Purkinje neurons in acutely prepared cerebellar slices. Neurons were loaded with calcium indicator Fura-2 by 40-min slice incubation in Tyrode solution containing 5 μM Fura-2/AM and 0.02% pluronic-F127. Bath applications of ATP (100 μM), epinephrine (10 μM) and histamine (100 μM) triggered a transient increase of [Ca²⁺]_i in Purkinje neurons. ATP-induced [Ca²⁺]_i elevation in Purkinje neurons was mimicked by ADP, but not AMP or adenosine pointing to the involvement of P2y metabotropic purinoreceptors. Epinephrine-triggered [Ca²⁺]_i responses were blocked by the selectiveα1-antagonist prazosin and were mimicked by theα1-adrenoreceptor agonist phenylephrine, and were not affected by β- andα2-adrenoreceptor agonists (isoproterenol and clonidine) and antagonists (propranolol and yohimbine). Histamine-induced [Ca²⁺]_i responses demonstrated specific sensitivity to selective H1 antagonist chlorpheniramine, and were not sensitive to H2 and H3 histamine receptors modulators. The [Ca²⁺]_i responses to all three agonists persisted in Ca²⁺-free extracellular media and were blocked by slice preincubation with thapsigargin (500 nM).

We conclude that cerebellar Purkinje neurons are endowed with metabotropic P2Y purinoreceptors,α1-adrenoreceptors and H1 histamine receptors which mediate the generation of intracellular [Ca2+]i signals via activation of Ca2+ release from inositol-1,4,5-trisphosphate-sensitive intracellular stores.