Temperature dependence of Na+/Ca2+ exchange activity in beef-heart sarcolemmal vesicles and proteoliposomes.
Temperature dependence of Na+/Ca2+ exchange activity was studied in beef cardiac sarcolemmal vesicles in the absence and presence of the inhibitor amiloride and in proteoliposomes reconstituted with different lipid mixtures. Arrhenius plots for Na+/Ca2+ exchange activity in both control and amiloride-treated vesicles revealed an apparent energy of activation of 9665 +/- 585 (SE, n = 4) cal/mol, corresponding to a temperature coefficient (Q10) value of 1.70 +/- 0.05 (SE, n = 4) over the range 25-37 degrees C. When Na+/Ca2+ exchange was reconstituted into phosphatidylcholine (PC):phosphatidylserine (PS) (52:48, mol/mol), PC:PS:cholesterol (25:39:36, mol/mol), and PC:PS:distearoylphosphatidylcholine (DSPC) (31:48:21, mol/mol) proteoliposomes, the highest activity was found in PC:PS:cholesterol proteoliposomes. Arrhenius plots of Na+/Ca2+ exchange activity exhibited breakpoints at 23 degrees C (PC:PS), 33 degrees C (PC:PS:cholesterol), and 23 degrees C (PC:PS:DSPC). The increase in the thermotropic transition temperature with cholesterol could result from the condensing effect of this sterol, whereas the breaks observed with PC:PS and PC:PS:DSPC could be caused by a non-lipid-mediated membrane protein conformational change. These results indicate that the lipid microenvironment around the Na+/Ca2+ exchanger and the nature of the specific lipid-protein interactions influence the activity of this antiporter. Further evidence supporting the hypothesis that cholesterol behaves as a specific positive effector for the exchanger is also given.
Debetto
P
P
Department of Pharmacology, University of Padova, Italy.
Cusinato
F
F
Luciani
S
S
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D007700:Kinetics; D008081:Liposomes; D008563:Membrane Lipids / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D011510:Proteolipids / Q000378:metabolism*; D012508:Sarcolemma / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013816:Thermodynamics
D008081:Liposomes; D008563:Membrane Lipids; D011510:Proteolipids; C020485:proteoliposomes; D000584:Amiloride; D012964:Sodium; D002118:Calcium