The (Ca2+-Mg2+)-ATPases of the plasma membrane and of the endoplasmic reticulum in smooth muscle cells and their regulation.
Smooth muscle cells contain two distinct Ca2+-transport ATpases with a different subcellular localization. The plasmalemmal Ca2+ pump has a relative molecular weight (Mr) of 140k and its phospho-intermediate level is increased by La3+. Its resemblance to the erythrocyte Ca2+ pump is further confirmed by its calmodulin-binding capacity and its antigenic properties. A 100k Ca2+-transport ATPase is localized in the endoplasmic reticulum. Its phospho-intermediate level is decreased by La3+, and it is antigenically related to the cardiac sarcoplasmic reticulum Ca2+-transport ATPase. These two different Ca2+-transport ATPases are present in both visceral and vascular smooth muscle, but tissue- and species-dependent differences in their relative amount have been observed. The endoplasmic-reticulum Ca2+-transport ATPase is regulated via phospholamban. Phosphorylation of this regulatory protein by cAMP-dependent as well as by cGMP-dependent protein kinase stimulates the endoplasmic-reticulum Ca2+ pump. The activity of the plasmalemmal Ca2+-transport ATPase can be modulated by calmodulin, negatively charged phospholipids, and by receptor-binding agonists. cGMP-dependent protein kinase also exerts a stimulatory effect on the plasmalemmal Ca2+ pump, but this effect is not mediated via a direct phosphorylation of the Ca2+ pump.
Eggermont
J A
JA
Laboratorium voor Fysiologie, Katholieke Universiteit Leuven, Belgium.
Vrolix
M
M
Wuytack
F
F
Raeymaekers
L
L
Casteels
R
R
D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology*; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D006801:Humans; D009131:Muscle, Smooth, Vascular / Q000201:enzymology*
D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases