The thapsigargin-sensitive intracellular Ca2+ pool is more important in plasma membrane Ca2+ entry than the IP3-sensitive intracellular Ca2+ pool in neuronal cell lines.
In NG108-15 cells, bradykinin (BK) and thapsigargin (TG) caused transient increases in a cytosolic free Ca2+ concentration ([Ca2+]i), after which [Ca2+]i elevated by TG only declined to a higher, sustained level than an unstimulated level. In PC12 cells, carbachol (CCh) evoked a transient increase in [Ca2+]i followed by a sustained rise of [Ca2+]i, whereas [Ca2+]i elevated by TG almost maintained its higher level. In the absence of extracellular Ca2+, the sustained elevation of [Ca2+]i induced by each drug we used was abolished. In addition, the rise in [Ca2+]i stimulated by TG was less affected after CCh or BK, whereas CCh or BK caused no increase in [Ca2+]i after TG. TG neither increased cellular inositol phosphates nor modified the inositol phosphates format on stimulated by CCh or BK. We conclude that TG may release Ca2+ from both IP3-sensitive and -insensitive intracellular pools and that some kinds of signalling to link the intracellular Ca2+ pools and Ca2+ entry seem to exist in neuronal cells.
Takemura
H
H
Department of Pharmacology, Sapporo Medical College, Japan.
Ohshika
H
H
Yokosawa
N
N
Oguma
K
K
Thastrup
O
O
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000031:analogs & derivatives; D005910:Glioma; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007295:Inositol Phosphates / Q000378:metabolism*; D007700:Kinetics; D009447:Neuroblastoma; D009553:Nimodipine / Q000494:pharmacology; D016716:PC12 Cells; D010456:Peptides, Cyclic / Q000494:pharmacology; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D005456:Fluorescent Dyes; D007295:Inositol Phosphates; D010456:Peptides, Cyclic; D013729:Terpenes; D020960:omega-Conotoxins; C049925:fura-2-am; C053423:Conus magus toxin; D009553:Nimodipine; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D001920:Bradykinin; D002118:Calcium; D016257:Fura-2