Calcium entry pathways associated with TRPC proteins. TRPC proteins are proposed to form store operated and basal/receptor operated plasma membrane calcium channels (depicted in green). Receptor operated calcium entry can occur when an agonist (e.g. oxytocin or PGF2α) binds to its receptor (R) resulting in an increase in diacylglycerol (DAG) and IP3 (inositol 1,4,5-trisphosphate). Interaction of IP3 with the receptor (ITPR) causes release of calcium for the sarcoplasmic reticulum (SR) and initiates store operated calcium entry.