BERGMANN GLIAL-CELLS IN-SITU EXPRESS ENDOTHELIN(B) RECEPTORS LINKED TO CYTOPLASMIC CALCIUM SIGNALS

The endothelin (ET) isoforms ET-1, ET-2 and ET-3 applied at 100 nM tri ggered a transient increase in [Ca2+](i) in Bergmann glial cells in ce rebellar slices acutely isolated from 20-25 day-old mice. The intracel lular calcium concentration ([Ca2+](i)) was monitored using Fura-2-bas ed [Ca2+](i) microfluorimetry. The ET-triggered [Ca2+](i) transients w ere mimicked by ETB receptor agonist BQ-3020 and were inhibited by ETB receptor antagonist BQ-788. ET elevated [Ca2+](i) in Ca2+-free extrac ellular solution and the ET-triggered [Ca2+](i) elevation was blocked by 500 nM thapsigargin indicating that the [Ca2+](i) was released from InsP(3)-sensitive intracellular pools. The ET-triggered [Ca2+](i) inc rease in Ca2+-free solution was shorter in duration. Restoration of no rmal extracellular [Ca2+] briefly after the ET application induced a s econd [Ca2+](i) increase indicating the presence of a secondary Ca2+ i nflux which prolongs the Ca2+ signal. Pre-application of 100 mu M ATP or 10 mu M noradrenaline blocked the ET response suggesting the involv ement of a common Ca2+ depot. The expression of ETB receptor mRNAs in Bergmann glial cells was revealed by single-cell RT-PCR. The mRNA was also found in Purkinje neurones, but no Ca2+ signalling was triggered by ET. We conclude that Bergmann glial cells are endowed with function al ETB receptors which induce the generation of intracellular [Ca2+](i ) signals by activation of Ca2+ release from InsP(3)-sensitive intrace llular stores followed by a secondary Ca2+ influx.