Excitation-contraction coupling model to estimate the recirculating fraction of activator calcium in intact cardiac muscle
| Autor: | L L Hefner, Alfred A. Walker, Russell C. Reeves, Ferdinand Urthaler |
|---|---|
| Rok vydání: | 1990 |
| Předmět: |
Cardiac Complexes
Premature Physiology chemistry.chemical_element Calcium In Vitro Techniques Models Biological Feedback Catecholamines Cytosol Physiology (medical) medicine Carnivora Animals Papillary muscle Pharmacology biology Activator (genetics) Electromyography Myocardium Fissipedia Excitation–contraction coupling Cardiac muscle Ferrets Heart General Medicine Anatomy Papillary Muscles biology.organism_classification Myocardial Contraction Acetylcholine Electric Stimulation medicine.anatomical_structure chemistry Circulatory system Biophysics |
| Zdroj: | Canadian journal of physiology and pharmacology. 68(8) |
| ISSN: | 0008-4212 |
| Popis: | Potentiated contractions were evoked with a rapid pace pause maneuver in 14 length-clamped ferret papillary muscles paced 12 times/min at 25 °C. At 1.25 mM [Ca2+]o the average steady-state force was 2.94 ± 1.08 g/mm2 and the potentiated contraction averaged 10.96 ± 1.61 g/mm2. At 5.0 mM [Ca2+]o the steady-state force increased to 6.18 ± 1.23 g/mm2 and the potentiated contraction averaged 12.08 ± 1.15 g/mm2. Under the conditions of these experiments the potentiated contraction obtained at 5.0 mM [Ca2+]o is equal to the maximum twitch tension (Fmax) these muscles can generate. We have previously shown that Fmax is an equivalent of maximal calcium activated force. Since there is a beat to beat nearly exponential decay of the evoked potentiation, the fraction (= fraction x) of the potentiation that is not dissipated with each beat is nearly constant. Using an excitation–contraction coupling model we have previously found that x reflects a measure of the recirculating fraction of activator calcium. Because the tension–calcium relationship is better characterized by a sigmoidal curve, we have now incorporated the Hill equation in the model. To account for the inverse relationship between [Ca2+]i and the magnitude of the slow inward current, a term for negative feedback (h) was also included. We have determined the quantity (x – h) because x and h could not be determined separately. The quantity (x – h) was denoted as x′. The average values of x′ at 1.25 and 5.0 mM [Ca2+]o were significantly different (p 2+]o and about 50% at the higher [Ca2+]o. An attempt to estimate both x′ and the Hill coefficient N simultaneously has shown that the determination of N must be considered inaccurate, but even larger variations of N have little influence on x′. Thus, in intact ferret ventricular muscle, the model predicts that at 1.25 mM [Ca2+]o only about 20% of the activator calcium recirculates, while some 80% comes across the sarcolemma from the extracellular compartment. The model also predicts that the recirculating fraction doubles when [Ca2+]o is elevated to 5 mM.Key words: length-clamped papillary muscle, maximum twitch tension, excitation–contraction coupling model, recirculating fraction of activator calcium, transsarcolemmal fraction of activator calcium. |
| Databáze: | OpenAIRE |
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