ACTIVATION OF P-2-PURINORECEPTORS, ALPHA(1)-ADRENORECEPTORS AND H-1-HISTAMINE RECEPTORS TRIGGERS CYTOPLASMIC CALCIUM SIGNALING IN CEREBELLAR PURKINJE NEURONS

The cytoplasmic concentration ([Ca2+](i)) was measured from Purkinje n eurons in acutely prepared cerebellar slices. Neurons were loaded with calcium indicator Fura-2 by 40-min slice incubation in Tyrode solutio n containing 5-mu-M Fura-2/AM and 0.02% pluronic-F127. Bath applicatio ns 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 i nduced [Ca2+](i) elevation in Purkinje neurons was mimicked by ADP, bu t not AMP or adeonsine pointing to the involvement of P-2Y metabotropi c purinoceptors. Epinephrine-triggered [Ca2+](i) responses were blocke d by the selective alpha(1)-antagonist prazosin and were mimicked by t he alpha(1)-adrenoceptor agonist phelylephrine, and were not affected by beta- and alpha(2)-adrenoceptor agonists (isoproterenol and clonidi ne) and antagonists (propranolol and yohimbine). Histamine-induced [Ca 2+](i) responses demonstrated specific sensitivity to selective H-1 an tagonist chlorpheniramine, and were not sensitive to H-2 and H-3 hista mine receptors modulators. The [Ca2+](i) responses to all three agonis ts persisted in [Ca2+](i)-free extracellular media and were blocked by slice perincubation with thapsigargin (500nM). We conclude that cereb bellar Purkinje neurons are endowed with metabotropic P-2Y purinocepto rs, 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.