Thyroid status and regulation of intracellular sodium in rabbit heart.
To examine the effect of thyroid status on the homeostatic control of intracellular Na+, we studied the effect of treatment of hypothyroid rabbits with 3,5,3'-triiodothyronine (T3). Intracellular Na+ and pH (pHi) in papillary muscles and Na+-K+ pump current (Ip) in ventricular myocytes were measured with ion-sensitive microelectrode and whole cell patch-clamp techniques. Na+ influx, estimated from the rate of increase in intracellular Na+ on sudden Na+-K+ pump blockade with dihydroouabain, and Na+ efflux, calculated from Ip, were similar. Treatment with T3 induced an increase in both Na+ influx and Ip. The treatment-induced increase in Na+ influx was eliminated by 5-(N,N-dimethyl)amiloride (DMA) but not by tetrodotoxin. Treatment with T3 increased the rate of fall in pHi on exposure of the papillary muscles to DMA; when the buffer capacity was taken into account, the T3 treatment-induced increase in this rate corresponded well with the treatment-induced, DMA-inhibitable estimate of Na+ uptake. We conclude that thyroid hormone enhances both Na+-H+ exchange-mediated Na+ uptake and Na+-K+ pump-mediated Na+ efflux.
Doohan
M M
MM
Department of Cardiology, Royal North Shore Hospital, and University of Sydney, New South Wales, Australia.
Gray
D F
DF
Hool
L C
LC
Robinson
B G
BG
Rasmussen
H H
HH
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006352:Heart Ventricles; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D007037:Hypothyroidism / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D010042:Ouabain / Q000031:analogs & derivatives / Q000494:pharmacology; D010210:Papillary Muscles / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D011441:Propylthiouracil; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology; D013961:Thyroid Gland / Q000502:physiology*; D014284:Triiodothyronine / Q000494:pharmacology*
D014284:Triiodothyronine; C000977:dihydroouabain; C039465:5-dimethylamiloride; D013779:Tetrodotoxin; D010042:Ouabain; D011441:Propylthiouracil; D000584:Amiloride; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase