This protein is found as a pentamer and is a major substrate for the cAMP-dependent protein kinase (
PKA) in cardiac muscle. In the unphosphorylated state, phospholamban is an inhibitor of cardiac muscle sarcoplasmic reticulum Ca2+-ATPase (
SERCA2)[7] which transports calcium from
cytosol into the
sarcoplasmic reticulum. When
phosphorylated (by PKA) - disinhibition of Ca2+-ATPase of SR leads to faster Ca2+ uptake into the sarcoplasmic reticulum, thereby contributing to the
lusitropic response elicited in heart by
beta-agonists.[8] The protein is a key regulator of
cardiac diastolic function. Mutations in this gene are a cause of inherited human
dilated cardiomyopathy with refractory
congestive heart failure.[9]
When phospholamban is phosphorylated by PKA, its ability to inhibit SERCA2 is lost.[10] Thus, activators of PKA, such as the beta-adrenergic agonist
epinephrine (released by
sympathetic stimulation), may enhance the rate of cardiac myocyte relaxation. In addition, since SERCA2 is more active, the next
action potential will cause an increased release of calcium, resulting in increased contraction (positive
inotropic effect). When phospholamban is not phosphorylated, such as when PKA is inactive, it can interact with and inhibit SERCA. Thus, the overall effect of unphosphorylated phospholamban is to decrease
contractility and the rate of
muscle relaxation, thereby decreasing
stroke volume and
heart rate, respectively.[11]
^Rodriguez P, Kranias EG (December 2005). "Phospholamban: a key determinant of cardiac function and dysfunction". Archives des Maladies du Coeur et des Vaisseaux. 98 (12): 1239–43.
PMID16435604.
^Hagemann D, Xiao RP (February 2002). "Dual site phospholamban phosphorylation and its physiological relevance in the heart". Trends in Cardiovascular Medicine. 12 (2): 51–6.
doi:
10.1016/S1050-1738(01)00145-1.
PMID11852250.
^Schmitt JP, Kamisago M, Asahi M, Li GH, Ahmad F, Mende U, Kranias EG, MacLennan DH, Seidman JG, Seidman CE (February 2003). "Dilated cardiomyopathy and heart failure caused by a mutation in phospholamban". Science. 299 (5611): 1410–3.
doi:
10.1126/science.1081578.
PMID12610310.
S2CID12253445.