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Trifluoperazine inhibition of contraction in permeabilized skeletal, cardiac and smooth muscles
1Albert Einstein College of Medicine, Department of Medicine and Physiology/Biophysics, Bronx, NY 10461.
Abstract:
To gain insights into the mechanism of the central helix of calmodulin and troponin-C in the Ca2(+)-regulation of force development in striated and smooth muscles, the present study was made of the TFP induced inhibition of contraction, and of the uptake of these proteins by skinned fibers. Calmodulin was four-fold more sensitive to TFP than TnC, but the inhibition was found to be identical for skeletal and cardiac muscles despite the differences in their troponin-C isoforms. Also, the results were comparable between fast-twitch fiber, when calmodulin was exchanged for troponin-C to act on TnI, and smooth muscle, where calmodulin acts on myosin light chain kinase. These findings indicate that the inhibition of force by TFP is entirely due to its binding to the hydrophobic sites in the central helix. The uptakes of troponin-C and calmodulin were also different, and this is explained by a TFP-independent domain in troponin-C that binds TnI.
Insights
Trifluoperazine (TFP) inhibits muscle contraction by binding to the central helix of calmodulin and troponin-C. This mechanism is consistent across different muscle types, highlighting TFP
Area of Science:
- Muscle Physiology
- Biochemistry
- Molecular Biology
Background:
- Calmodulin and troponin-C are key calcium-binding proteins regulating muscle contraction.
- The central helix plays a crucial role in the function of these proteins.
- Understanding their mechanisms is vital for muscle function research.
Purpose of the Study:
- To investigate the mechanism of trifluoperazine (TFP) induced inhibition of muscle contraction.
- To determine the role of the central helix of calmodulin and troponin-C in Ca2(+)-regulation.
- To compare the effects of TFP on different muscle types and protein isoforms.
Main Methods:
- Studying TFP-induced inhibition of contraction in skinned muscle fibers.
- Measuring the uptake of calmodulin and troponin-C by skinned fibers.
- Exchanging calmodulin and troponin-C in fast-twitch fibers to assess functional impact.
Main Results:
- Calmodulin showed higher sensitivity to TFP than troponin-C.
- TFP inhibition was consistent across skeletal and cardiac muscles, irrespective of troponin-C isoforms.
- Results were comparable between fast-twitch fibers and smooth muscle, indicating a conserved inhibitory mechanism.
- TFP's inhibitory effect is attributed to binding hydrophobic sites in the central helix.
- Differences in protein uptake suggest a TFP-independent binding domain in troponin-C for troponin-I.
Conclusions:
- Trifluoperazine (TFP) inhibits muscle force development by binding to the central helix of calmodulin and troponin-C.
- The mechanism of TFP inhibition is conserved across different muscle types and protein isoforms.
- A TFP-independent domain in troponin-C facilitates binding to troponin-I, influencing protein uptake.