title: Vasopressin-, angiotensin II-, and alpha 1-adrenergic-induced inhibition of Ca2+ transport by rat liver plasma membrane vesicles.
abstract: A rapid method for isolating highly purified rat liver plasma membrane vesicles using isotonic medium and Percoll self-forming gradient centrifugation is described. The vesicles were characterized by enzyme markers and electron microscopy. The method also yielded a fraction rich in nuclei. The vesicles transported Ca2+ in an ATP-dependent manner and this was enhanced by oxalate. The Vmax for Ca2+ uptake was 0.65 +/- 0.08 nmol/mg X min, which was approximately 18-fold higher than for other liver plasma membrane preparations, and the Km for Ca2+ was 5.2 +/- 0.4 nM. Calcium uptake was inhibited by 40-50% in vesicles isolated from rat livers perfused for 3 min with 10(-7)M vasopressin. The half-maximally effective concentration of vasopressin was 5 X 10(-10)M which correlates with that for raising cytosolic Ca2+ and phosphorylase a. Inhibition was not significant in vesicles from livers perfused with vasopressin for only 1 min, indicating that inhibition of the Ca2+ pump may not be involved in the rise in cytosolic Ca2+ observed at 1-2 s with this hormone. Epinephrine (10(-5)M) and angiotensin II (10(-7)M) inhibited Ca2+ uptake by 31 +/- 10 and 26 +/- 5%, respectively, at 3 min. Glucagon (10(-7)M) had no effect. It is proposed that the inhibitory action of the Ca2+-dependent hormones on the plasma membrane Ca2+ pump plays an important role in the actions of these hormones by prolonging the elevation in cytosolic Ca2+.
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004837:Epinephrine / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010477:Perfusion; D051381:Rats; D011919:Rats, Inbred Strains; D014667:Vasopressins / Q000494:pharmacology*
chemical_list: D014667:Vasopressins; D000804:Angiotensin II; D002118:Calcium; D004837:Epinephrine