Involvement of intracellular stores in the Ca2+ responses to N-Methyl-D-aspartate and depolarization in cerebellar granule cells.
The [Ca2+]i of cerebellar granule cells can be increased in a biphasic manner by addition of NMDA or by depolarization (induced by elevating the extracellular K+ level), which both activate Ca2+ influx. The possibility that these stimuli activate Ca2(+)-induced Ca2+ release was investigated using granule cells loaded with fura 2-AM. Dantrolene, perfused onto groups of cells during the sustained plateau phase of the [Ca2+]i response to K+ or NMDA, was found to reduce the response to both agents in a concentration-dependent manner. Preincubation with thapsigargin (10 microM) substantially reduced the plateau phase of the [Ca2+]i response to K+ and both the peak and plateau phases of the NMDA response. Preincubation with ryanodine (10 microM) also reduced both the K(+)-evoked plateau response and both phases of the NMDA response. Neither had a consistent effect on the peak response to K+. The effects of thapsigargin and ryanodine on the NMDA response were partially additive. These results demonstrate that in cerebellar granule cells a major component of both K(+)- and NMDA-induced elevation of [Ca2+]i appears to be due to release from intracellular stores. The partial additivity of the effects of thapsigargin and ryanodine suggests that these agents affect two overlapping but nonidentical Ca2+ pools.
Simpson
P B
PB
Department of Pharmacology and Therapeutics, University of Leicester, England.
Challiss
R A
RA
Nahorski
S R
SR
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002531:Cerebellum / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D003620:Dantrolene / Q000494:pharmacology; D004594:Electrophysiology; D016202:N-Methylaspartate / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012433:Ryanodine / Q000494:pharmacology; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D013729:Terpenes; D012433:Ryanodine; D016202:N-Methylaspartate; D019284:Thapsigargin; D003620:Dantrolene; D011188:Potassium; D002118:Calcium