CALCIUM SIGNALING IN GRANULE NEURONS STUDIED IN CEREBELLAR SLICES

The cytoplasmic free calcium concentration ([Ca2+](i)) was studied in Fura-2/AM loaded granule neurones in acutely prepared cerebellar slice s isolated from neonatal (6 days old) and adult (30 days old) mice. Ba th application of elevated (10-50 mM) KCl-containing extracellular sol utions evoked [Ca2+](i) rise which was dependent on extracellular Ca2. The K+-induced [Ca2+](i) elevation was inhibited to different extend s by verapamil, nickel and omega-conotoxin suggesting the coexpression of different subtypes of plasmalemmal voltage-gated Ca2+ channels. Ba th application of caffeine (10-40 mM) elevated [Ca2+](i) by release of Ca2+ from intracellular stores. Caffeine-induced [Ca2+](i) elevation was inhibited by 100 mu M ryanodine and 500 nM thapsigargin. Depletion of internal Ca2+ stores by caffeine, or blockade of Ca2+ release chan nels by ryanodine, did not affect depolarization-induced [Ca2+](i) tra nsients, suggesting negligible involvement of Ca2+-induced Ca2+ releas e in [Ca2+](i) signal generation following cell depolarization. Extern al application of 100 mu M glutamate, but not acetylcholine (1-100 mu M), carbachol (10-100 mu M) or (1S,3R)-ACPD (100-500 mu M) evoked [Ca2 +](i) elevation. Part of glutamate-triggered [Ca2+](i) transients in n eurones from neonatal mice was due to Ca2+ release (presumably via ino sitol-(1,4,5)-trisphosphate-sensitive mechanisms) from internal Ca2+ s tores. In adult animals, glutamate-triggered [Ca2+](i) elevation was e xclusively associated with plasmalemmal Ca2+ influx via both voltage-g ated and glutamate-gated channels.