ABSTRACT
The myometrium undergoes several changes in its expression during pregnancy. The threshold for activation of the myometrium decreases during pregnancy. Because in myometrium the Ca2+ pumps are the major mechanisms for decreasing Cai, their expression and regulation during pregnancy and delivery is important to understand. The plasma membrane Ca2+ pumps are activated by calmodulin and the cardiac sarcoplasmic reticulum pump is inhibited by phospholamban. The molecular structures of the Ca2+ pumps and how the structures are related to diversity of their action is being investigated by recombinant DNA techniques. The products of the PMCA transcripts have all been found to contain a calmodulin binding domain as well as binding sites for adenosine triphosphate, and Ca2+. The calmodulin binding domain is characterized by a predominance of basic amino acids with hydrophobic residues and a high probability of forming an amphipathic helix upon binding to calmodulin.
