Specifically, because calcium is linked to adenosine (ADO) levels that, together with cAMP, modulate A2AR activity in PC12 cells to reproduce cellular aberrations found in PD [17]–[20] we first measured cellular levels of adenosine triphosphate (ATP), which provide energy to activate the plasma membrane Ca2+ ATPase (PMCA) and also is an upstream source of ADO. This evidence concerns the gene ADORA2A and Parkinson disease.