1. Triiodothyronine reverses depressed contractile performance after excessive catecholamine stimulation 
Tomasz Timek, MD, Christian-Friedrich Vahl, MD, Andreas Bonz, MD, Leo Schäffer, Mark Rosenberg, Siegfried Hagl, MD 
The Annals of Thoracic Surgery 
Volume 66, Issue 5, Pages (November 1998)
DOI: /S (98)

2. Fig 1
Superimposed isometric contractions of isolated trabeculae before (1) and after (2) triiodothyronine (T3) incubation in a normal porcine left ventricular muscle fiber. The slight abbreviation and the increase of the amplitude of the intracellular calcium transient and the acceleration of the time course of the isometric contraction are clearly visible.
The Annals of Thoracic Surgery  , DOI: ( /S (98) )

3. Fig 2
Effect of triiodothyronine (T3) application in an isolated porcine left ventricular trabeculum that was incubated for 6 hours with epinephrine. Note that after T3 application the isometric force amplitude (upper trace) and the amplitude of shortening (lower trace) increased considerably. (Epi = epinephrine.)
The Annals of Thoracic Surgery  , DOI: ( /S (98) )

4. Fig 3
Illustration of the effect of triiodothyronine (T3) application after a 6-hour period of epinephrine incubation on intracellular calcium transient and force as illustrated by an original recording. Note that systolic calcium (peak value of the calcium transient) remains nearly unaltered in this muscle, while diastolic calcium declines. This is accompanied by a dramatic decline of resting tension and a considerable increase of the isometric force amplitude. (Epi = epinephrine.)
The Annals of Thoracic Surgery  , DOI: ( /S (98) )

5. Fig 4
Digitized and averaged recordings of 60 sequential isometric contractions before and after triiodothyronine (T3) application (upper trace, intracellular calcium transient; lower trace, isometric force). Trace (1) represents averaged recordings after long-term, high-dose epinephrine exposure; curve (2) indicates recordings measured after T3 application. Note that after T3 treatment the amplitude of the intracellular calcium transient declines considerably. The diastolic decay of the calcium transient is accelerated. However, despite the considerable reduction of the amplitude of the intracellular calcium transient the force amplitude did not decline. There was even a slight increase. The time course of both contraction and relaxation was accelerated. An unchanged force amplitude measured at a reduced intracellular calcium transient provides direct evidence that the contractile apparatus becomes more sensitive to calcium after T3 application (sensitization of the contractile apparatus to calcium). (Epi = epinephrine.)
The Annals of Thoracic Surgery  , DOI: ( /S (98) )

6. Fig 5
Illustration of some effects mediated by high-dose catecholamine stimulation. Improved contractile performance is caused by increased intracellular calcium levels after catecholamine stimulation. When catecholamine exposure persists a cyclic adenosine monophosphate (cAMP)-dependent phopsphorylation of troponin I is induced, which in turn is associated with negative inotropic effects (reduced calcium sensitivity of the contractile apparatus and retarded actomyosin adenosine triphosphatase activity). A parallel cAMP-dependent phosphorylation of myosin light chains (LC) induces an enhancement of the myofibrillar adenosine triphosphatase activity correlating positively with the contractile performance. The catalytic activity of the protein phosphatase 2B increases with rising intracellular calcium concentrations and acts on phosphorylated myosin-light chains when intracellular calcium remains elevated. As a result the negative inotropic effect of troponin I phosphorylation overrides the positive effects of myosin light chain phosphorylation when both phosphorylation processes occur in the presence of high intracellular calcium loads.
The Annals of Thoracic Surgery  , DOI: ( /S (98) )