MODULATION OF MUSCARINIC SIGNALING IN PC12 CELLS OVEREXPRESSING NEURONAL CA2+ SENSOR-1 PROTEIN

It has been suggested that overexpression of neuronal Ca2+ sensor-1 (NCS-1) protein is implicated in the pathophysiology of neurodisorders such as schizophrenia, bipolar disturbance and X-linked mental retardation. The mechanism by which NCS-1 would be involved in the causes and/or consequences of these neurodisorders is still far from elucidation. Independent evidence has pointed NCS-1 as a key regulator of synaptic efficacy by altering the expression and activity of voltage-gated channels, inhibiting internalization of dopaminergic receptors, and altering phosphoinositide metabolism. In this study, we examined the possible participation of NCS-1 protein in signal transmission dependent on muscarinic receptor activation, using PC12 cells stably expressing NCS-1 (PC12-NCS-1). Carbachol (CCH; 300 mu M) was able to evoke glutamate release more efficiently from PC12-NCS-1 (15.3 +/- 1.0nmol/mg of protein) than wild type cells (PC12-wt; 8.3 +/- 0.9nmol/mg of protein). This increase of glutamate release induced by CCH was independent on extracellular Ca2+ influx. Additionally, a larger increase of cytoplasmic levels of InsP(3) (663.0 +/- 63.0 and 310.0 +/- 39.0% of fluorescence in A.U.) and [Ca2+](i) (766.4 +/- 40.0 and 687.8 +/- 37.1nmol/L) was observed after CCH stimulus of PC12-NCS-1 compared with PC12-wt. Clearly distinction between intracellular Ca2+ dynamics was also observed in PC12-NCS-1 and PC12-wt. A larger increase followed by fast decay of [Ca2+](i) was observed in PC12-NCS-1. A plateau with a delayed decay of [Ca2+](i) was characteristic of PC12-wt [Ca2+](i) response. Both enhancement of InsP3 production and glutamate release observed in PC12-NCS-1 were blocked by atropine (10 mu M). Together, our data show that overexpression of NCS-1 in PC12 cells induces an enhancement of intracellular second messenger and transmitter release dependent on CCH response, suggesting that muscarinic signaling is "up-regulated" in this cell model.