Claim: Oscillation of Ca concentration is directly affected by the signal-transduction activity of P2Y1 (functions as a receptor for extracellular ATP and ADP), which is linked to a signal cascade originating in regulation of the flow of Ca and K ions by the receptor's interactions with G proteins.
Evidence: Oscillation of Ca concentration is directly affected by the signal-transduction activity of P2Y1; specifically, through protein kinase C phosphorylation of Thr339 in the carboxy terminus of the P2Y1 receptor. Found in all known forms of life, ATP is often referred to as the "molecular unit of currency" of intracellular energy transfer. P2Y receptors are a family of purinergic G protein-coupled receptors, stimulated by nucleotides such as ATP, ADP, UTP, UDP and UDP-glucose. The activity of P2Y receptors is linked to a signal cascade originating in regulation of the flow of Ca and K ions by the receptor's interactions with G proteins, modulating access to Ca and K channels, though the exact behavior is dependent upon individual receptor species. P2Y receptors respond either positively or negatively to the presence of nucleotides in extracellular solution.