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

Abstract Intracellular Ca 2 + levels are tightly regulated in the neuronal system. The loss of Ca 2 + 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 Ca 2 + signaling in PC-12 cells. The stimulation of NGF-differentiated PC-12 cells with 3 μM ATP caused an early Ca 2 + release followed by a delayed Ca 2 + release. The delayed Ca 2 + release was dependent on prior ATP priming and on dopamine secretion by PC-12 cells. Delayed Ca 2 + 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 Ca 2 + release. Given the importance of calcyon in clathrin-mediated endocytosis, we verified the role of this protein in the delayed Ca 2 + release phenomenon. siRNA targeting of calcyon blocked the delayed Ca 2 + release, decreased ATP-evoked IP 3 R-mediated Ca 2 + release, and impaired subsequent Ca 2 + oscillations. Our results suggested that calcyon is involved in an unknown mechanism that causes a delayed IP 3 R-mediated Ca 2 + release in PC-12 cells. In schizophrenia, Ca 2 + dysregulation may depend on the upregulation of calcyon, which maintains elevated Ca 2 + levels as well as dopamine signaling.