Activation of P-2-purino-, alpha(1)-adreno and H-1-histamine receptors triggers cytoplasmic calcium signalling in cerebellar Purkinje neurons

The cytoplasmic 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-mu-M Fura-2/AM and 0.02% pluronic-F127. Bath applications of ATP (100-mu-M), epinephrine (10-mu-M) sand histamine (100-mu-M) 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 adeonsine pointing to the involvement of P-2Y metabotropic purinoceptors. Epinephrine-triggered [Ca2+](i) responses were blocked by the selective alpha(1)-antagonist prazosin and were mimicked by the alpha(1)-adrenoceptor agonist phelylephrine, and were not affected by beta- and alpha(2)-adrenoceptor agonists (isoproterenol and clonidine) and antagonists (propranolol and yohimbine). Histamine-induced [Ca2+](i) responses demonstrated specific sensitivity to selective H-1 antagonist chlorpheniramine, and were not sensitive to H-2 and H-3 histamine receptors modulators. The [Ca2+](i) responses to all three agonists persisted in [Ca2+](i)-free extracellular media and were blocked by slice perincubation with thapsigargin (500nM). We conclude that cerebbellar Purkinje neurons are endowed with metabotropic P-2Y purinoceptors, alpha(1)-adrenoceptor and H-1 histamine receptors wich mediate the generation of intracellular [Ca2+](i) signals via activation of [Ca2+](i) release from inositol-1,4,5-triphosphate-sensitive intracellular stores.