Aorta phospholamban

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... 

Phospholamban was initially detected in smooth muscle in purified ER preparations from pig stomach and rabbit aorta as electrophoretic bands comigrating with the 25-kDa pentameric and 5-kDa monomeric forms of cardiac phospholamban. The dissociation of the pentamer depends on the conditions of pretreatment of the sample with the denaturing electrophoresis buffer. Phospholamban protein has also been detected in many other vascular and gastrointestinal smooth muscles, including rat aortic cells (Sarcevic et al, 1989 Karczewski et ai, 1992), canine ileum and iliac artery (Ferguson et al., 1988), and bovine aorta (L. Raeymaekers, unpublished observations Watras,... 

However, phospholamban protein was undetectable in pig aorta (Raeymaekers and Jones, 1986 Eggermont etfl/., 1990b). To our knowledge, published data on myometrium are lacking. The amino acid sequence of phospholamban of pig stomach smooth muscle determined from cDNA sequencing is identi-... 

The level of phospholamban protein relative to that of SERCA Ca2+-ATPase in isolated ER vesicles from smooth muscle has been compared in bovine aorta (Watras, 1988), in bovine main pulmonary artery, and in several smooth muscles of the pig (Eggermont etal, 1990b). Watras (1988) and Raeymaekers et al. (1990) found a ratio of approximately 1. A possible drawback of these experiments is that they depended on the preservation of the pump s activity during isolation of the membranes. In the porcine smooth muscles investigated by Eggermont et al. (1990b), the level of phospholamban protein relative to that of SERCA2 protein was smaller than in cardiac muscle (Fig. 2). It is not clear whether this different result is due to the tissue difference or to the use of a more reliable method. 

Especially relevant are studies on the phosphorylation of phospholamban in smooth muscle cells in vivo. Cornwell et al. (1991) and Karczewski et al. (1992) convincingly demonstrated phosphorylation of phospholamban in rat aorta incubated with agents that increase cGMP. 

Karczewski, P., Kelm, M., Hartmann, M., etal. (1992). Role of phospholamban in NO/EDRF-induced relaxation in rat aorta. Life Sci. 51, 1205-1210. 

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