Na(+)-Ca2+ exchangers from rod outer segments and cardiac sarcolemma: comparison of properties.
The properties of the Na(+)-Ca2+ exchangers from cardiac sarcolemma (SL) and rod outer segments (ROS) were studied in parallel by measuring the Na+ gradient-dependent Ca2+ uptake into SL or ROS vesicles. The ROS exchanger, but not the SL exchanger, has a striking specific dependence on K+. The ROS exchanger is stimulated by K+ with an apparent concentration at half-maximum of 1 mM. The addition of valinomycin, to produce an inside-positive membrane potential, stimulates the SL exchanger 1.8-fold and the ROS exchanger 1.2-fold. The Michaelis constant for half-maximal transport rate for Ca2+ and the maximal transport rate for the exchangers, in the absence of valinomycin, are estimated to be 20 microM and 8 nmol.mg-1.2.2 s-1 in SL and 5 microM and 1 nmol.mg-1.2.2 s-1 in ROS. Both exchangers are modulated by the same regulatory influences. For example, both are stimulated by proteases, phospholipase D, and intravesicular Ca2+.
Nicoll
D A
DA
Department of Medicine, University of California, School of Medicine, Los Angeles 90024-1760.
Barrios
B R
BR
Philipson
K D
KD
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle; D004285:Dogs; D004533:Egtazic Acid / Q000494:pharmacology; D010450:Endopeptidases / Q000494:pharmacology; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D012374:Rod Cell Outer Segment / Q000378:metabolism*; D012508:Sarcolemma / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger; D014634:Valinomycin / Q000494:pharmacology
D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D014634:Valinomycin; D004533:Egtazic Acid; D010450:Endopeptidases; D011188:Potassium; D002118:Calcium