Calcium signalling in mouse Bergmann glial cells mediated by alpha(1)-adrenoreceptors and H-1 histamine receptors

The presence of adrenergic and histaminergic receptors in Bergmann glial cells from cerebellar slices from mice aged 20-25 days was determined using fura-2 Ca2+ microfluorimetry. To measure the cytoplasmic concentration of Ca2+ ([Ca2+](i)), either individual cells were loaded with the Ca2+-sensitive probe fura-2 using the whole-cell patch-clamp technique or slices were incubated with a membrane-permeable form of the dye (fura-2/AM) and the microfluorimetric system was focused on individual cells. The monoamines adrenalin and noradrenalin (0.1-10 mu M) and histamine (10-100 mu M) triggered a transient increase in [Ca2+](i). The involvement of the alpha(1)-adrenoreceptor was inferred from the observations that monoamine-triggered [Ca2+](i) responses were blocked by the selective alpha(1)-adreno-antagonist prazosin and were mimicked by the alpha(1)-adreno-agonist phenylephrine. The monoamine-induced [Ca2+](i) signals were not affected by beta- and alpha(2)-adrenoreceptor antagonists (propranolol and yohimbine), and were not mimicked by beta- and alpha(2)-adrenoreceptor agonists (isoproterenol and clonidine). Histamine-induced [Ca2+](i) responses demonstrated specific sensitivity to only H-1 histamine receptor modulators. [Ca2+](i) responses to monoamines and histamine did not require the presence of extracellular Ca2+ and they were blocked by preincubation of slices with thapsigargin (500 nM), indicating that the [Ca2+](i) increase is due to release from intracellular pools. No [Ca2+](i) responses were recorded after application of aspartate, bradykinin, dopamine, GABA, glycine, oxytocin, serotonin, somatostatin, substance P, taurine or vasopressin. We conclude that cerebellar Bergmann glial cells are endowed with alpha(1)-adrenoreceptors and H-1 histamine receptors which induce the generation of intracellular [Ca2+](i) signals via activation of Ca2+ release from inositol-1,4,5-trisphosphate-sensitive intracellular stores.