Regulation of the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA 2a) depends on 
the phosphorylation state of phospholamban (PLB). When PLB is phosphorylated, 
its inhibitory effect towards SERCA 2a is relieved, leading to an enhanced 
myocardial performance. This process is reversed by a sarcoplasmic reticulum 
(SR)-associated type 1 protein phosphatase (PP1) composed of a catalytic subunit 
PP1C and a regulatory subunit GM. Human GM and PLB have been produced in an in 
vitro transcription/translation system and used for co-immunoprecipitation and 
biosensor experiments. The detected interaction between the two partners 
suggests that cardiac PPI is targeted to PLB via GM and we believe that this 
process occurs with the identified transmembrane domains of the two proteins. 
Thus, the interaction between PLB and GM may represent a specific way to 
modulate the SR function in human cardiac muscle.