Identification of a peptide inhibitor of the cardiac sarcolemmal Na(+)-Ca2+ exchanger.
The deduced amino acid sequence of the cardiac sarcolemmal Na(+)-Ca2+ exchanger has a region which could represent a calmodulin binding site. As calmodulin binding regions of proteins often have an autoinhibitory role, a synthetic peptide with this sequence was tested for functional effects on Na(+)-Ca2+ exchange activity. The peptide inhibits the Na(+)-dependent Ca2+ uptake (KI approximately 1.5 microM) and the Nao(+)-dependent Ca2+ efflux of sarcolemmal vesicles in a noncompetitive manner with respect to both Na+ and Ca2+. The peptide is also a potent inhibitor (KI approximately 0.1 microM) of the Na(+)-Ca2+ exchange current of excised sarcolemmal patches. The binding site for the peptide on the exchanger is on the cytoplasmic surface of the membrane. The exchanger inhibitory peptide binds calmodulin with a moderately high affinity. From the characteristics of the inhibition of the exchange of sarcolemmal vesicles, we deduce that only inside-out sarcolemmal vesicles participate in the usual Na(+)-Ca2+ exchange assay. This contrasts with the common assumption that both inside-out and right-side-out vesicles exhibit exchange activity.
Li
Z
Z
Department of Medicine, UCLA School of Medicine 90024-1760.
Nicoll
D A
DA
Collins
A
A
Hilgemann
D W
DW
Filoteo
A G
AG
Penniston
J T
JT
Weiss
J N
JN
Tomich
J M
JM
Philipson
K D
KD
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D002352:Carrier Proteins / Q000037:antagonists & inhibitors*; D002417:Cattle; D008969:Molecular Sequence Data; D009206:Myocardium / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012508:Sarcolemma / Q000737:chemistry*; D019831:Sodium-Calcium Exchanger
D002147:Calmodulin; D002352:Carrier Proteins; D010455:Peptides; D019831:Sodium-Calcium Exchanger; C066745:exchanger inhibitory peptide; D002118:Calcium