Ca transients from Ca channel activity in rat cardiac myocytes reveal dynamics of dyad cleft and troponin C Ca binding
| Autor: | David Redon, Dennis M. Heisey, Sivan Vadakkadath Meethal, Robert A. Haworth, Katherine T. Potter |
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| Rok vydání: | 2003 |
| Předmět: |
medicine.medical_specialty
Time Factors Fura-2 Physiology Binding Competitive Troponin C chemistry.chemical_compound Adenosine Triphosphate Internal medicine medicine Myocyte Animals Myocytes Cardiac Binding site Fluorescent Dyes Binding Sites biology Chemistry Endoplasmic reticulum Electric Conductivity Models Cardiovascular Cell Biology Troponin Rats Coupling (electronics) Endocrinology Biophysics biology.protein Calcium Female Calcium Channels Adenosine triphosphate |
| Zdroj: | American journal of physiology. Cell physiology. 286(2) |
| ISSN: | 0363-6143 |
| Popis: | The properties of the dyad cleft can in principle significantly impact excitation-contraction coupling, but these properties are not easily amenable to experimental investigation. We simultaneously measured the time course of the rise in integrated Ca current ( ICa) and the rise in concentration of fura 2 with Ca bound ([Ca-fura 2]) with high time resolution in rat myocytes for conditions under which Ca entry is only via L-type Ca channels and sarcoplasmic reticulum (SR) Ca release is blocked, and compared these measurements with predictions from a finite-element model of cellular Ca diffusion. We found that 1) the time course of the rise of [Ca-fura 2] follows the time course of integrated ICaplus a brief delay (1.36 ± 0.43 ms, n = 6 cells); 2) from the model, high-affinity Ca binding sites in the dyad cleft at the level previously envisioned would result in a much greater delay (≥3 ms) and are therefore unlikely to be present at that level; 3) including ATP in the model promoted Ca efflux from the dyad cleft by a factor of 1.57 when low-affinity cleft Ca binding sites were present; 4) the data could only be fit to the model if myofibrillar troponin C (TnC) Ca binding were low affinity (4.56 μM), like that of soluble troponin C, instead of the high-affinity value usually used (0.38 μM). In a “good model,” the rate constants for Ca binding and dissociation were 0.375 times the values for soluble TnC; and 5) consequently, intracellular Ca buffering at the rise of the Ca transient is inferred to be low. |
| Databáze: | OpenAIRE |
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