A Tale of two receptors.

Calcium (Ca) oscillations in hepatocytes have a wide dynamic range. In particular, recent experimental evidence shows that agonist stimulation of the P2Y family of receptors leads to qualitatively diverse Ca oscillations. We present a new model of Ca oscillations in hepatocytes based on these experiments to investigate the mechanisms controlling P2Y-activated Ca oscillations. The model accounts for Ca regulation of the IP receptor (IPR), the positive feedback from Ca on phospholipase C (PLC) and the P2Y receptor phosphorylation by protein kinase C (PKC). Furthermore, PKC is shown to control multiple cellular substrates. Utilising the model, we suggest the activity and intensity of PLC and PKC necessary to explain the qualitatively diverse Ca oscillations in response to P2Y receptor activation.