New concepts of endoplasmic reticulum function in the heart: Programmed to conserve

► Secreted and membrane proteins are made in the ER and the SR of cardiac myocytes. ► These molecules mediate cellular communication and signal transduction in the heart. ► The ER and SR communicate energy needs to the rest of the cell. ► This process is regulated as part of the ER stress response. ► Signals from the ER integrate cellular energy, metabolism, and growth.