ITPR1 and hydrops fetalis: In HF, PKA phosphorylation of IP3R1 channels seems to be a major pathway involved in vasoconstriction, since it is directly linked to increased levels of catecholamines, whereas tyrosine kinase phosphorylation would shift the Ca2+ dependence of inactivation of IP3R1 to higher values of cytoplasmic [Ca2+] ([Ca2+]cyt).