Expression of isoforms of internal Ca2+ pump in cardiac, smooth muscle and non-muscle tissues.
Smooth muscle and several non-muscle tissues contain mRNA for an alternative splice of the mRNA for the cardiac sarcoplasmic reticulum (SR) Ca,Mg-ATPase. Based on amino acid composition deduced from cDNA sequences the cardiac isoform (Ic) is 110 kDa while the smooth muscle and the non-muscle isoform (Is) is 115 kDa. This prediction in their molecular masses was tested at the protein level in rabbit stomach, aorta, uterus and vas deferens smooth muscles; stomach mucosa, brain, liver, kidney and heart. The major species of the acylphosphates formed in the presence of Ca2+ and electrophoresed in acid SDS-acrylamide gels were 5 kDa smaller for the heart (Ic) than those for all the other tissues (Is). The size difference was also confirmed in Western blots using a monoclonal antibody which binds to both Is and Ic. Thus consistent with the mRNA splices for the internal Ca2+ pumps previously reported to be present in these tissues, rabbit heart expresses predominantly the Ca2+ pump protein Ic and the various smooth muscle, mucosa, brain, liver and kidney express mainly the isoform Is.
Spencer
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Department of Biomedical Sciences, McMaster University Health Sciences Center, Hamilton, Ontario, Canada.
Yu
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Khan
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Grover
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D000818:Animals; D000911:Antibodies, Monoclonal; D001693:Biological Transport, Active; D001921:Brain / Q000201:enzymology; D000252:Calcium-Transporting ATPases / Q000737:chemistry / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism*; D008970:Molecular Weight; D009130:Muscle, Smooth / Q000201:enzymology*; D009206:Myocardium / Q000201:enzymology*; D011817:Rabbits
D000911:Antibodies, Monoclonal; D007527:Isoenzymes; D000252:Calcium-Transporting ATPases