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The thrombin receptor elevates intracellular calcium in adult rat ventricular myocytes
T Jiang1, P Danilo, S F Steinberg
1Department of Pharmacology, Columbia University, New York, NY 10032, USA.
Insights
Thrombin receptor activation increases intracellular calcium and muscle contraction in heart cells. This study reconciles previous findings on thrombin
Area of Science:
- Cardiovascular Physiology
- Cellular Biology
- Molecular Pharmacology
Background:
- Thrombin receptor activation's effect on cardiac intracellular calcium is debated.
- Previous studies show conflicting results on thrombin's role in cardiomyocyte calcium modulation.
Purpose of the Study:
- To investigate thrombin receptor activation's impact on intracellular calcium in adult ventricular myocytes.
- To reconcile discrepant findings regarding thrombin and cardiomyocyte calcium levels.
Main Methods:
- Utilized a thrombin receptor-derived agonist peptide (SFLLRN) on isolated adult ventricular myocytes.
- Tested control peptide (FLLRN) and a PAR-2 selective ligand (SLIGRL).
- Assessed isometric contraction force in intact rat papillary muscles.
Main Results:
- SFLLRN increased cytosolic calcium and twitch amplitude in isolated myocytes, but only at high concentrations.
- Thrombin itself was inactive; SFLLRN's effects were specific to thrombin receptor activation.
- Enzymatic cell isolation procedures may affect thrombin receptor function, as SFLLRN increased contraction in intact muscles at lower concentrations.
Conclusions:
- Thrombin receptor activation demonstrably increases intracellular calcium in adult ventricular myocytes.
- This activation also elicits a positive inotropic response in ventricular myocardium.
- Findings reconcile previous discrepancies and highlight the role of experimental conditions in observing cellular responses.
Abstract:
While there is evidence that thrombin receptor activation leads to contractile dysfunction and induces arrhythmias in ischemic/reperfused cardiac tissue, thrombin is variably reported to modulate intracellular calcium in cardiomyocytes. The present study demonstrates that thrombin receptor activation leads to a rise in intracellular calcium in adult ventricular myocytes and serves to reconcile previous discrepant findings. The thrombin receptor-derived agonist peptide (SFLLRN, a portion of the tethered ligand created by thrombin's proteolytic actions) increases cytosolic calcium and twitch amplitude in cardiomyocytes isolated from adult ventricles. The truncated control peptide FLLRN has no effect, establishing that the response to SFLLRN results from a specific agonist peptide-receptor interaction. However, the response to SFLLRN occurs only at high agonist peptide concentrations and thrombin itself is inactive. This result is not compatible with an action of SFLLRN at a distinct protease-activated receptor (PAR-2; which is activated by SFLLRN, but not by thrombin), since SLIGRL (a ligand which is selective for PAR-2, but not the thrombin receptor) has no effect. Rather, the enzyme-based cell isolation procedure may partially cleave the thrombin receptor and influence cell responses, since concentrations of SFLLRN which are sub-threshold in enzymatically disaggregated myocytes significantly increase the force of isometric contraction of intact rat papillary muscles. These studies provide the first evidence that thrombin receptor activation leads to a change in intracellular calcium and a positive inotropic response in adult ventricular myocardium.