Short term effect of low doses of tri-iodothyronine on proximal tubular membrane Na-K-ATPase and potassium permeability in thyroidectomized rats.
Tri-iodothyronine (T3), even when administered for short time and at low doses, induces a large increase in the isotonic fluid reabsorption (Jv) in proximal tubules of thyroidectomized rats (TX). In order to investigate the role of the Na-K-ATPase in this process, we measured the Na-K-ATPase activity in early proximal convoluted tubules (S1) and proximal straight tubules (S2) microdissected from TX rats and rats treated with low doses of T3 (10 micrograms/kg body wt), either for 3 days (TX + 3T3) or for 7 days (TX + 7T3). In both segments no changes in Na-K-ATPase activity were found in TX + 3T3 rats versus TX rats, while an increase was registered in TX + 7T3 rats. Using micropuncture techniques, Jv measured on the same tubular segments increased by 68% in TX + 3T3 rats versus TX. Thus, no correlation between Jv and Na-K-ATPase activity measured in vitro could be detected after short term treatment of TX rats with T3. Na-K-ATPase activity in vivo is also regulated by the potassium permeability of the membrane, which might be altered by tri-iodothyronine. This hypothesis was tested by perfusing intraluminally and peritubularly proximal tubules of TX rats with the K ionophore, valinomycin (1 microgram/ml). In the dual perfusion experiments valinomycin elicited 40% of the action induced on Jv by 3 days treatment with T3. On the other hand, no further increase in Jv was recorded when valinomycin was applied in TX rats pretreated with T3.(ABSTRACT TRUNCATED AT 250 WORDS)
Capasso
G
G
Lin
J T
JT
De Santo
N G
NG
Kinne
R
R
D000042:Absorption; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase; D007687:Kidney Tubules, Proximal / Q000201:enzymology* / Q000378:metabolism; D008297:Male; D008566:Membranes / Q000201:enzymology; D009399:Nephrons / Q000201:enzymology; D010539:Permeability; D011188:Potassium / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013965:Thyroidectomy; D013997:Time Factors; D014284:Triiodothyronine / Q000008:administration & dosage* / Q000494:pharmacology; D014634:Valinomycin / Q000494:pharmacology
D014284:Triiodothyronine; D014634:Valinomycin; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium