Key Points
- To identify and characterize the relaxing protein system and tropomyosin in vascular smooth muscle actomyosin regulation.
- Desensitized natural arterial actomyosin by precipitation at ionic strength I = 0.22 to separate soluble regulatory components.
- Measured superprecipitation and Mg2+-activated adenosine triphosphatase (ATPase) activity in the presence and absence of Ca2+ and isolated protein fractions.
- Characterized the protein components using polyacrylamide gel electrophoresis and cross-tested functionality with skeletal troponin complex and tropomyosin.
- Removal of the soluble protein fraction allowed arterial actomyosin to superprecipitate without Ca2+ and increased Mg2+-ATPase activity 7-fold.
- Re-addition of the soluble arterial protein fraction or addition of skeletal troponin complex restored inhibition of superprecipitation and Mg2+-ATPase activity, whereas tropomyosin alone did not inhibit activity.
- Polyacrylamide gel electrophoresis demonstrated that tropomyosin was the principal component of the soluble relaxing fraction, showing functional and electrophoretic identity to skeletal tropomyosin.
Structured PICO
PPopulationVascular smooth muscle (natural arterial actomyosin)
IInterventionDesensitisation by precipitation at I=0.22 and replacement of soluble protein fraction
CComparatorNatural arterial actomyosin
OOutcomeSuperprecipitation and Mg2+-activated adenosine triphosphatase activitysurrogate
Demonstrates the existence of a relaxing protein system in vascular smooth muscle that functions similarly to that in striated muscle.