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Myosin regulatory light chain diphosphorylation slows relaxation of arterial smooth muscle

Cindy Sutherland1, Michael P Walsh

  • 1Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada.

The Journal of Biological Chemistry
|June 5, 2012
PubMed

Insights

Phosphorylation of myosin light chains (LC(20)) at Thr(18) slows smooth muscle relaxation. This diphosphorylation, alongside Ser(19) phosphorylation, may explain hypercontractility in vasospasm and hypertension.

Area of Science:

  • Biochemistry
  • Physiology
  • Molecular Biology

Background:

  • Smooth muscle contraction is primarily signaled by myosin light chain (LC(20)) phosphorylation at Ser(19) via Ca(2+)/calmodulin-dependent myosin light chain kinase.
  • Inhibition of myosin light chain phosphatase can lead to Ca(2+)-independent phosphorylation at Ser(19) and Thr(18) by kinases like ILK and ZIPK.

Purpose of the Study:

  • To investigate the functional effects of Thr(18) phosphorylation on steady-state isometric force and relaxation rate in smooth muscle.
  • To determine how diphosphorylation of LC(20) at both Ser(19) and Thr(18) impacts muscle function compared to monophosphorylation.

Main Methods:

  • Triton-skinned rat caudal arterial smooth muscle strips were used to study muscle function.
  • Sequential phosphorylation was induced using adenosine 5'-O-(3-thiotriphosphate) and microcystin (phosphatase inhibitor).
  • Steady-state force, dephosphorylation rates, and relaxation rates were measured for monophosphorylated and diphosphorylated LC(20).

Main Results:

  • Phosphorylation at Thr(18) did not affect steady-state force induced by Ser(19) phosphorylation.
  • Comparable levels of isometric force were achieved with monophosphorylated (Ser(19)) and diphosphorylated (Ser(19) and Thr(18)) LC(20).
  • Diphosphorylation significantly decreased the rates of LC(20) dephosphorylation and smooth muscle relaxation compared to monophosphorylation.

Conclusions:

  • Phosphorylation at Thr(18) significantly slows the dephosphorylation of LC(20) and smooth muscle relaxation.
  • LC(20) diphosphorylation may contribute to hypercontractility observed in physiological and pathological conditions.
  • These findings offer insights into mechanisms underlying vasospasm, intimal hyperplasia, and hypertension.

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