The Na+-Ca2+ exchange system in vascular smooth muscle cell membrane vesicles isolated from cultured cells and from tissue is similar.
The existence of a Na+-Ca2+ exchange system was investigated in sarcolemmal vesicles isolated from cultured cells of dog mesenteric artery. When Na+-loaded membrane vesicles were suspended in a Na+-free KCl medium to create an outwardly directed Na+ concentration gradient across the membrane, a time-dependent uptake of Ca2+ was observed. This uptake of Ca2+ was drastically reduced when the vesicles were suspended in NaCl medium to eliminate the Na+ concentration gradient across the membrane. Monensin also decreased Ca2+ uptake in Na+-loaded vesicles. The apparent Km for Ca2+ was 2.97 microM and the apparent maximum velocity was 4.27 nmol/min per mg protein. The data indicate that a Na+-Ca2+ exchange system exists in sarcolemmal membranes isolated from cultured cells and that it is similar to the system in membranes isolated from the tissue.
Matlib
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MA
Department of Pharmacology and Cell biophysics, University of Cincinnati College of Medicine, OH 45267-0575.
Kihara
M
M
Farrell
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C
Dage
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RC
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000302:isolation & purification* / Q000378:metabolism; D002478:Cells, Cultured; D004285:Dogs; D008297:Male; D008565:Membrane Proteins / Q000302:isolation & purification* / Q000378:metabolism; D008638:Mesenteric Arteries / Q000032:analysis; D009131:Muscle, Smooth, Vascular / Q000032:analysis*; D011188:Potassium / Q000378:metabolism*; D012508:Sarcolemma / Q000032:analysis; D019831:Sodium-Calcium Exchanger
D002352:Carrier Proteins; D008565:Membrane Proteins; D019831:Sodium-Calcium Exchanger; D011188:Potassium; D002118:Calcium