title: Effects of thyroid hormone on action potential and repolarizing currents in rat ventricular myocytes.
abstract: Thyroid hormones play an important role in cardiac electrophysiology through both genomic and nongenomic mechanisms of action. The effects of triiodothyronine (T(3)) on the electrophysiological properties of ventricular myocytes isolated from euthyroid and hypothyroid rats were studied using whole cell patch clamp techniques. Hypothyroid ventricular myocytes showed significantly prolonged action potential duration (APD(90)) compared with euthyroid myocytes, APD(90) of 151 +/- 5 vs. 51 +/- 8 ms, respectively. Treatment of hypothyroid ventricular myocytes with T(3) (0.1 microM) for 5 min significantly shortened APD by 24% to 115 +/- 10 ms. T(3) similarly shortened APD in euthyroid ventricular myocytes, but only in the presence of 4-aminopyridine (4-AP), an inhibitor of the transient outward current (I(to)), which prolonged the APD by threefold. Transient outward current (I(to)) was not affected by the acute application of T(3) to either euthyroid or hypothyroid myocytes; however, I(to) density was significantly reduced in hypothyroid compared with euthyroid ventricular myocytes.
authors.affiliation: Pediatric Cardiology, New York University Medical Center, New York 10016, USA.
authors.forename: Z Q
authors.initials: ZQ
authors.lastname: Sun
authors.forename: K
authors.initials: K
authors.lastname: Ojamaa
authors.forename: W A
authors.initials: WA
authors.lastname: Coetzee
authors.forename: M
authors.initials: M
authors.lastname: Artman
authors.forename: I
authors.initials: I
authors.lastname: Klein
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D019256:Cadmium Chloride / Q000494:pharmacology; D004553:Electric Conductivity; D006321:Heart / Q000187:drug effects* / Q000503:physiopathology*; D006352:Heart Ventricles / Q000187:drug effects / Q000503:physiopathology; D007037:Hypothyroidism / Q000139:chemically induced / Q000503:physiopathology; D008297:Male; D018408:Patch-Clamp Techniques; D011441:Propylthiouracil; D051381:Rats; D017207:Rats, Sprague-Dawley; D014284:Triiodothyronine / Q000494:pharmacology*; D014285:Triiodothyronine, Reverse / Q000494:pharmacology
chemical_list: D014284:Triiodothyronine; D014285:Triiodothyronine, Reverse; D011441:Propylthiouracil; D015761:4-Aminopyridine; D019256:Cadmium Chloride