Cohen JE, Fields RD. CaMKII inactivation by extracellular Ca(2+) depletion in dorsal root ganglion neurons.
Cell Calcium 2006;
39:445-54. [PMID:
16519936 PMCID:
PMC2365305 DOI:
10.1016/j.ceca.2006.01.005]
[Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2005] [Revised: 11/21/2005] [Accepted: 01/21/2006] [Indexed: 10/24/2022]
Abstract
A mechanism by which Ca(2+)/CaM-dependent protein kinase (CaMKII) is autophosphorylated by changes in extracellular calcium in the absence of detectable changes in cytoplasmic [Ca(2+)] has been identified. We find that when the external Ca(2+) concentration ([Ca(2+)](O)) is lowered, Ca(2+) is released from intracellular stores to maintain a constant cytoplasmic Ca(2+) level, gradually depleting the endoplasmic Ca(2+) stores. Accompanying the store-depletion is a rapid decrease in CaMKII activity. Approximately 25% of the measured CaMKII autophosphorylation in DRG neurons in culture can be regulated by Ca(2+) flux from intracellular stores caused by manipulating [Ca(2+)](O), as shown by blocking refilling of store-operated Ca(2+)-channels with SK&F 96365, Ruthenium Red, and a partial block with Ni(2+). Blocking voltage-gated Ca(2+)-channels with either isradipine or SR 33805, had no effect on CaMKII autophosphorylation induced by restoring Ca(2+)(O) to normal after depleting the intracellular Ca(2+) stores. These results show that removal of Ca(2+)(O) has profound effects on intracellular Ca(2+) signaling and CaMKII autophosphorylation, in the absence of measurable changes in intracellular Ca(2+). These findings have wide-ranging significance, because [Ca(2+)](O) is manipulated in many experimental studies. Moreover, this explanation for the paradoxical changes in CaMKII phosphorylation in response to manipulating [Ca(2+)](O) provides a possible mechanism linking activity-dependent depletion of Ca(2+) from the synaptic cleft to a protein kinase regulating many neuronal properties.
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