title: Calcium metabolism and depressed contractility in isolated human and porcine heart muscle.
abstract: Contractility is often depressed in isolated heart muscle. To analyze this phenomenon, we measured the derivative of left ventricular pressure (dP/dt) in intact and in isolated, blood perfused pig hearts, and peak force (F) or stress (F/mm2) in ventricular trabeculae of man and pig. When the heart was in the steady state at a priming frequency of 2 Hz an extrasystolic interval of 0.3 s was interposed, followed by four postextrasystolic intervals of 0.8 s. In the case of isolated trabeculae the priming frequency was 0.2 Hz, the extra interval 0.4 s, and the post-extrasystolic intervals were 5 s. The exponential decay of potentiation is characterized by the constant D: a low value of D indicates a rapid decay of potentiation. DP/dt was about 1000 mm Hg/s in the intact hearts, but within 1 h after isolation dP/dt decreased to about 700 mm Hg/s, and this was associated with a decrease in D from 0.63 to 0.40. Developed stress in the isolated trabeculae was about 2 mN/mm2 and D was about 0.20 under standard, in vitro conditions (a.o. 1.5 mM Ca2+. 0.2 Hz stimulus frequency). This stress is only 10% of the calculated stress in the intact heart. An increase of priming frequency, or of [Ca2+], or addition of 30 nM isoproterenol to the perfusate caused a marked increase in F and D. Properties of human and porcine trabeculae were quantitatively similar. The strong correlation between dP/dt, or F, and D suggests a causal relationship. This is consistent with the current model of e-c coupling in heart muscle, in which the activity of the Ca2+ pump of the sarcoplasmic reticulum determines the decay of potentiation and the amount of releasable Ca2+ in the reticulum determines force of contraction. Since isoproterenol stimulates the Ca2+ pump in the reticulum, the increase in D and F induced by this drug is consistent with the model. We conclude, that the decreased dP/dt, F, and D in isolated preparations was due to impaired sarcoplasmic reticulum function. The role of this phenomenon in the stunned heart syndrome, species differences and possible causes are discussed.
authors.affiliation: Department of Thoracic Surgery, University of Leiden, The Netherlands.
authors.forename: V J
authors.initials: VJ
authors.lastname: Schouten
authors.forename: J J
authors.initials: JJ
authors.lastname: Schipperheyn
authors.forename: G L
authors.initials: GL
authors.lastname: van Rijk-Zwikker
authors.forename: G P
authors.initials: GP
authors.lastname: Swier
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005117:Cardiac Complexes, Premature / Q000503:physiopathology; D004594:Electrophysiology; D006321:Heart / Q000502:physiology*; D006706:Homeostasis; D006801:Humans; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D009994:Osmolar Concentration; D013552:Swine
chemical_list: D007545:Isoproterenol; D002118:Calcium