Mechanism of dopamine D2 receptor-induced Ca2+ release in PC-12 cells

Intracellular Ca2+ levels are tightly regulated in the neuronal system. The loss of Ca2+ homeostasis is associated with many neurological diseases and neuropsychiatric disorders such as Parkinson's, Alzheimer's, and schizophrenia. We investigated the mechanisms involved in intracellular Ca2+ signaling in PC-12 cells. The stimulation of NGF-differentiated PC-12 cells with 3 mu M ATP caused an early Ca2+ release followed by a delayed Ca2+ release. The delayed Ca2+ release was dependent on prior ATP priming and on dopamine secretion by PC-12 cells. Delayed Ca2+ release was abolished in the presence of spiperone, suggesting that it is due to the activation of D2 dopamine receptors (D2R) by dopamine secreted by PC-12 cells. This was shown to be independent of PKA activation but dependent on PLC activity. An endocytosis step was required for inducing the delayed Ca2+ release. Given the importance of calcyon in clathrin-mediated endocytosis, we verified the role of this protein in the delayed Ca2+ release phenomenon. siRNA targeting of calcyon blocked the delayed Ca2+ release, decreased ATP-evoked IP3R-mediated Ca2+ release, and impaired subsequent Ca2+ oscillations. Our results suggested that calcyon is involved in an unknown mechanism that causes a delayed IP3R-mediated Ca2+ release in PC-12 cells. In schizophrenia, Ca2+ dysregulation may depend on the upregulation of calcyon, which maintains elevated Ca2+ levels as well as dopamine signaling. (C) 2013 Published by Elsevier Inc.