Phospholamban

Sarcoplasmic calcium ATPase this enzyme utilizes the energy gained from hydrolysis of ATP to pump calcium from the cytosol into the stores of the sarcoplasmic reticulum. Its activity is negatively regulated by the closely associated protein phospholamban, and this inhibition is relieved upon phosphorylation of phospholamban by protein kinase A (PKA). 

Pan, Y., Kislinger, T., Gramolini, A.O., Zvaritch, E., Kranias, E.G., MacLennan, D.H., Emih, A. (2004). Identification of biochemical adaptations in hyper- or hypocontractile hearts from phospholamban mutant mice by expression proteomics. Proc. Natl. Acad. Sci. USA 101, 2241-2246. 

Phospholamban (PLB or PLN) is a single-pass, 52-residue integral membrane protein that regulates myocardial contractility by direct physical interaction with sarco(endo)plasmic reticulum Ca-ATPase (SERCA), a 110-kDa enzyme that maintains calcium homeostasis in the sarcoplasmic... 

The uniquely high resolution structural data available for the SERCAIa Ca2+ pump illuminates the structure of all P-type transporters. Unlike the Na,K pump, the catalytic subunit of the SERCA Ca2+ pumps is active and does not require association with another subunit. However, the cardiac isoform, SERCA-2a, associates with a small membrane protein, phospholamban, that can... 

Nelson We have the phospholamban knockout mouse model, and John Lederer was able to peel out a component of the decay that was due to reuptake. We didn t see any difference between the control and the knockouts. Presumably it is happening, but we couldn t see any difference in the decay in the phospholamban knockouts, as was seen in heart muscle, nor could we see any effect of lanthanum or zero Na+. Examining the decay of the spark would be a good indicator of local Ca2+ removal, though. It would also be worth examining the decay of the BK current. 

Blaustein As you say, you can t get the Ca2+ chelators in there to have a big effect, either. It must therefore be pretty local. Could there be local reuptake and does it have to be phospholamban-sensitive ... 

Nelson It could. We could try to load the SR. For example, we have used the phospholamban knockout mouse where it appears that the SR Ca2+ load increases (Wellman et al 2001). The spark frequency increases as the load increases. At the moment we have not observed any communication from the SR to the SK channels. 

Wellman GC, Santana LF, Bonev AD, Nelson MT 2001 Role of phospholamban in the modulation of arterial Ca2+ sparks and Ca2+-activated K+ channels by cAMP. Am J Physiol 281 C1029-0037... 

Eggermont JA, Wuytack F, Verbist J, Casteels R 1990 Expression of endoplasmic-reticulum Ca2+-pump isoforms and of phospholamban in pig smooth-muscle tissues. Biochem J... 

Karczewski P, Hendrischke T, Wolf WP, Morano I, Bartel S, Schrader J 1998 Phosphorylation of phospholamban correlates with relaxation of coronary artery induced by nitric oxide, adenosine, and prostacyclin in the pig. J Cell Biochem 70 49—59... 

Lalli J, Harrer JM, Luo W, Kranias EG, Paul RJ 1997 Targeted ablation of the phospholamban gene is associated with a marked decrease in sensitivity in aortic smooth muscle. Circ Res 80 506-513... 

Lalli MJ, Shimizu S, Sutliff RL, Kranias EG, Paul RJ 1999 [Ca2+]j homeostasis and cyclic nucleotide relaxation in aorta of phospholamban-deficient mice. Am J Physiol 277 H963— H970... 

Luo W, Grupp IL, Harrer J et al 1994 Targeted ablation of the phospholamban gene is associated with markedly enhanced myocardial contractility and loss of beta-agonist stimulation. Cite Res 75 401 —409... 

Nobe K, Sutliff RL, Kranias EG, Paul RJ 2001 Phospholamban regulation of bladder contractility evidence from gene-altered mouse models. J Physiol 535 867-878 Paul RJ 1998 The role of phospholamban and SERCA3 in regulation of smooth muscle-endothelial cell signalling mechanisms evidence from gene-ablated mice. Acta Physiol Scand 164 589—597... 

The main mechanisms that are important are (1) SERCA pumps (2) phospholamban (3) Ca2+ binding proteins (4) inositohl,4,5-trisphosphate (L1SP3) receptors and mechanisms involved in InsP3 production (5) ryanodine receptors and cADP ribose production and (6) the cytoskeleton. 

Phospholamban is a protein that inhibits the SERCA pumps by decreasing their affinity for Ca2+. It can be phosphorylated by protein kinase A, for instance in response to /1-adrenoceptor activation, resulting in inhibition of its effects and enhanced SERCA activity. The effects of phospholamban on contraction depend on the relative importance of Ca2+ uptake or release in the smooth muscle in... 

Nobe K, Sudiff RL, Kranias EG, Paul RJ 2001 Phospholamban regulation of bladder contractility evidence from gene-altered mouse models. J Physiol 535 867-878... 

Several of the proteins that mediate Ca2+ flow in and out of SR have been identified. Oxalate-facilitated Ca2+ uptake into the SR and in vitro biochemical studies of purified SR identified it as an ATP-driven Ca2+ pump (SERCA pump reviewed in Himpens et al 1995) that is inhibited by thapsigargin and cyclopiazonic acid and regulated, at least in some smooth muscles, by phosphorylation of phospholamban by cyclic nucleotide-activated protein kinase(s) (Karczewski et al 1998). 

Cardiac phospholamban (cardiac pump regulator) AIRRAST Intracellular [Ca2+]... 

Activity is modulated by other proteins present in the membrane. These include a glycoprotein (MW 53 000) which stimulates ATPase activity 138 a 60 000 molecular weight protein, which is phosphorylated in a calmodulin-dependent fashion, affects accumulation of calcium 139 while the activity of the enzyme is affected by an endogenous kinase and phosphatase which phosphorylates and dephosphorylates the protein.140 Phospholamban is a proteolipid (MW 22 000) in cardiac SR which undergoes both cyclic AMP-dependent and calcium-calmodulin-dependent phosphorylation,141 but at different sites. All these proteins are probably involved in regulating the activity of the calcium pump. 

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