Related Experiment Videos
Direct effects of thrombin on myocyte contractile function
R B Hird1, F A Crawford, R Mukherjee
1Division of Cardiothoracic Surgery, Medical University of South Carolina, Charleston 29425.
Insights
Thrombin directly impairs heart muscle cell function and response to beta-adrenergic stimulation. This suggests thrombin may contribute to heart dysfunction after cardiopulmonary bypass surgery.
Area of Science:
- Cardiovascular Physiology
- Biochemistry
Background:
- Cardiopulmonary bypass (CPB) elevates thrombin levels.
- Thrombin influences various cell types, suggesting potential cardiac effects.
Purpose of the Study:
- To investigate the direct impact of thrombin on left ventricular myocyte contractile function.
- To assess thrombin's effect on myocyte beta-adrenergic responsiveness.
Main Methods:
- Isolated adult dog left ventricular myocytes were studied using videomicroscopy.
- Myocyte function was measured at baseline and with increasing thrombin concentrations (1-10 U/mL).
- The effect of thrombin inhibition (hirudin) and beta-adrenergic stimulation (isoproterenol) was evaluated.
Main Results:
- Thrombin reduced myocyte shortening in a dose-dependent manner (e.g., 43% reduction at 2 U/mL).
- Hirudin completely blocked thrombin's negative effects on myocyte function.
- Thrombin significantly blunted beta-adrenergic responsiveness, reducing shortening velocity by 25%.
Conclusions:
- Thrombin directly impairs ventricular myocyte contractility and beta-adrenergic responsiveness.
- Elevated thrombin levels post-CPB may contribute to transient left ventricular dysfunction.
Abstract:
Cardiopulmonary bypass activates the clotting cascade, resulting in elevated circulating levels of thrombin. In light of the fact that the function of a wide variety of cell types is modulated by thrombin, we hypothesized that thrombin may have a direct effect on myocyte function. Isolated left ventricular myocyte contractile function was measured from 6 adult dogs using videomicroscopy at baseline and after increasing concentrations of thrombin (1 to 10 U/mL). Indices of myocyte contractile function were reduced in a dose-dependent manner in the presence of increasing concentrations of thrombin. For example, myocyte percent shortening fell by 18% with 1 U/mL thrombin and by 43% with 2 U/mL thrombin. The addition of hirudin, a highly selective thrombin inhibitor, completely blocked the effects of thrombin on myocyte contractile function. beta-Adrenergic agonists are commonly used in the early post-cardiopulmonary bypass period. Accordingly, a final set of experiments examined the effects of thrombin on myocyte beta-adrenergic responsiveness using isoproterenol (25 nmol/L). In myocytes preincubated with 1 U/mL thrombin, myocyte beta-adrenergic responsiveness was significantly reduced. For example, in the presence of 1 U/mL thrombin, myocyte velocity of shortening fell by 25% from isoproterenol alone values. The results from the present study provide evidence that thrombin has a direct negative effect on steady-state contractile function and beta-adrenergic responsiveness in adult mammalian ventricular myocytes. These findings suggest that thrombin may be an additional contributory factor toward the transient left ventricular dysfunction that has been observed after cardiopulmonary bypass.