Altered coupling states between calcium transport and (Ca2+, Mg2+)-ATPase in the AS-30D ascites hepatocarcinoma plasma membrane.
Plasma membrane fractions from normal, regenerating liver and the AS-30D ascites hepatocarcinoma exhibited a high degree of enrichment when a set of plasma membrane enzyme markers were studied in comparison to the ones associated to the mitochondrial and cytosolic compartments. While the (Ca2+, Mg2+)-ATPase observed for the plasma membrane fraction isolated from normal liver showed an activity of 1.2 mumoles/mg/min, the regenerating liver and the AS-30D plasma membrane fractions presented a much lower ATPase activity (0.3 and 0.22 mumoles/mg/min respectively). Despite the differences in ATPase activity observed between models, the plasma membrane fraction from the AS-30D hepatocarcinoma presented a calcium transport activity similar to the value observed for the normal system (5.9 and 5.5 nmoles Ca2+/mg/10 min, respectively). Interestingly, the ATP in equilibrium with Pi exchange experiments carried out with the different plasma membrane fractions revealed that the (Ca2+, Mg2+)-ATPase contained in the plasma membrane from the AS-30D cells shows an exchange activity of 26 nmoles ATP in equilibrium with Pi/mg/min, similar to the one observed fo the enzyme from normal liver (30 nmoles ATP in equilibrium with Pi/mg/min). Our results suggest that the plasma membrane from the transformed model presents a more efficient mechanism to regulate the movement of calcium through the calcium pump, with an optimum expenditure of energy.
Mas-Oliva
J
J
Departamento de Bioenergética, Universidad Nacional Autónoma de México.
Pérez-Montfort
R
R
Cárdenas-García
M
M
Rivas-Duro
M
M
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic / Q000378:metabolism; D003570:Cytidine Triphosphate / Q000378:metabolism; D003902:Detergents; D006160:Guanosine Triphosphate / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007293:Inosine Triphosphate / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008114:Liver Neoplasms, Experimental; D008115:Liver Regeneration; D008297:Male; D017830:Octoxynol; D011092:Polyethylene Glycols; D051381:Rats; D011919:Rats, Inbred Strains; D012965:Sodium Chloride / Q000494:pharmacology; D014638:Vanadates / Q000494:pharmacology
D003902:Detergents; D007293:Inosine Triphosphate; D014638:Vanadates; D011092:Polyethylene Glycols; D012965:Sodium Chloride; D003570:Cytidine Triphosphate; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D017830:Octoxynol; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium