Effect of triiodo-L-thyronine treatment on Ca2+ sequestration in rat liver microsomes.
T3 administration to rats exerts quite different effects on enzyme activities associated to liver microsomal membranes such as G-6-Pase, Mg ATPase and Ca2(+)-dependent ATPase: in fact G-6-Pase activity is significantly enhanced, Mg ATPase is not affected whereas Ca2(+)-dependent ATPase is drastically inhibited. The T3 induced decrease in Ca2(+)-dependent ATPase activity is associated with a net reduction (to about 50% with respect to controls) of the Ca2+ sequestration in liver microsomal vesicles. The enhanced level of inorganic phosphate in the endoplasmic reticulum due to the stimulation of G-6-Pase activity does not significantly affect the uptake of calcium in microsomal vesicles. The decreased Ca2(+)-dependent ATPase activity is associated to an enhanced level of the enzyme in the phosphorylated form (E-P). This suggests that in liver preparations from T3 treated rats the turnover of ATP and cleavage of E-P is reduced, thus resulting in the accumulation of the phosphorylated intermediate. The accumulation of E-P is in agreement with the inhibition of the calcium sequestration since the active transport of this cation in microsomal membranes requires the hydrolysis of the E-P complex.
Balestrero
F
F
Istituto di Fisiologia Generale, Università, Genova.
Morelli
A
A
Damonte
G
G
Voci
A
A
Orunesu
M
M
D000818:Animals; D001693:Biological Transport, Active; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D005952:Glucose-6-Phosphatase / Q000378:metabolism; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D008970:Molecular Weight; D010750:Phosphoproteins / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014284:Triiodothyronine / Q000494:pharmacology*
D010750:Phosphoproteins; D014284:Triiodothyronine; D005952:Glucose-6-Phosphatase; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium