Lysophospholipid-mediated alterations in the calcium transport systems of skeletal and cardiac muscle sarcoplasmic reticulum |
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Authors: | Indu S. Ambudkar El-Sayed Abdallah Adil E. Shamoo |
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Affiliation: | (1) Membrane Biochemistry Research Laboratory, Department of Biological Chemistry, University of Maryland, School of Medicine, 21201 Baltimore, Maryland, USA;(2) Present address: Clinical Investigations and Patient Care Branch N.I.D.R. NIH, 20205 Bethesda, Maryland, USA;(3) Present address: Department of Chemistry of Pesticides, Faculty of Agriculture, Alexandria University, Alexandria, Egypt;(4) Dept. Biol. Chem., University of Maryland, School of Medicine, 660, W. Redwood Street, 2120 Baltimore, MD, USA |
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Abstract: | Summary The effects of various lysophospholipids on the calcium transport activity of sarcoplasmic reticulum (SR) from rabbit skeletal and canine cardiac muscles were examined. The lipids decreased calcium transport activity in both membrane types; the effectiveness being in the order lysoPC > lsyoPS, lysoPG > lysoPE. The maximum inhibition induced by lysoPC, lysoPG and lysoPS was greater than 85% of the normal Ca2+-transport rate. In cardiac SR lysoPE had a maximal inhibition of about 50%. Half maximal inhibition of calcium transport by lysoPC was achieved at 110 nmoles lysoPC/mg SR. At this concentration of lysoPC, the (Ca2+ + Mg2+)-ATPase and Ca2+-uptake activities were inhibited to the same extent (about 60%) in skeletal sarcoplasmic reticulum, while in cardiac sarcoplasmic reticulum, there was less than 20% inhibition of the Ca2+ + Mg2+-ATPase activity. Studies with EGTA-induced passive calcium efflux showed that up to 200 nmoles lysoPC/mg SR did not alter calcium permeability significantly in cardiac sarcoplasmic reticulum. In skeletal muscle membranes the lysophospholipid mediated decrease in calcium uptake correlated well with the increase in passive calcium efflux due to lysophosphatidylcholine. The difference in the lysophospholipid-induced effects on the sarcoplasmic reticulum from the two muscle types probably reflects variations in protein and other membrane components related to the respective calcium transport systems. |
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Keywords: | calcium transport sarcoplasmic reticulum lysophospholipids |
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