Co‐expression of slow‐twitch/cardiac muscle Ca2+‐ATPase (SERCA2) and phospholamban

Abstract
Full length cDNAs encoding both slow‐twitch/cardiac (SERCA2) and fast‐twitch skeletal muscle (SERCA1) Ca2+‐ATPases were expressed by transient transfection of COS‐1 cells. Studies of the Ca2+‐dependency of Ca2+‐transport in microsomes isolated from these cells showed that both isoforms had an affinity for Ca2+ of about 0.2 μM. The Ca2+‐affinity of SERCA2 was lowered when phospholamban was co‐expressed with it, demonstrating that the two proteins interact in this expression system. These studies support the view that phospholamban inhibition accounts for the low Ca2+‐amnity and low activity of SERCA2 in cardiac muscle sarcoplasmic reticulum.