Thyroid status and Na(+)-K+ pump current, intracellular sodium, and action potential duration in rabbit heart.
Thyroid status influences the abundance of Na(+)-K+ pumps in the heart. To evaluate whether this phenomenon may contribute to a dependence of the action potential duration (APD) on thyroid status, we induced hypothyroidism in a group of New Zealand White rabbits. Another group was treated similarly but also received triiodothyronine (T3). Right ventricular myocytes were isolated and voltage clamped at -40 mV. We identified Na(+)-K+ pump current (Ipump) as a ouabain-induced shift in holding current. Mean Ipump, measured using patch pipettes containing 10 mM Na+, was 0.24 +/- 0.02 pA/pF in 9 cells from 4 hypothyroid rabbits and 0.48 +/- 0.05 in 10 cells from 4 rabbits treated with T3 (P < 0.001). Because thyroid status influences Na+ influx, we measured intracellular Na+ activity (aiNa) in right ventricular papillary muscles. We found that aiNa was 5.20 +/- 0.42 mM in nine papillary muscles from seven hypothyroid rabbits and 7.62 +/- 0.69 mM in nine papillary muscles from six rabbits treated with T3 (P < 0.01). The effect of thyroid-induced changes in Ipump and aiNa on APD was stimulated with a computer model. The simulations predicted that thyroid-induced changes in Ipump can influence APD. The predicted changes were similar to changes in APD measured in isolated papillary muscles.
Doohan
M M
MM
Department of Cardiology, Royal North Shore Hospital, Sydney, New South Wales, Australia.
Hool
L C
LC
Rasmussen
H H
HH
D000200:Action Potentials; D000818:Animals; D003198:Computer Simulation; D004553:Electric Conductivity; D006321:Heart / Q000502:physiology*; D007425:Intracellular Membranes / Q000378:metabolism*; D008297:Male; D008955:Models, Cardiovascular; D009206:Myocardium / Q000378:metabolism*; D011817:Rabbits; D011930:Reaction Time; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology*; D013961:Thyroid Gland / Q000502:physiology*
D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase