Altered kinetics of contraction of mouse atrial myocytes expressing ventricular myosin regulatory light chain

Am J Physiol. 1999 Apr;276(4):H1167-71. doi: 10.1152/ajpheart.1999.276.4.H1167.


To investigate the role of myosin regulatory light chain isoforms as a determinant of the kinetics of cardiac contraction, unloaded shortening velocity was determined by the slack-test method in skinned wild-type murine atrial cells and transgenic cells expressing ventricular regulatory light chain (MLC2v). Transgenic mice were generated using a 4.5-kb fragment of the murine alpha-myosin heavy chain promoter to drive high levels of MLC2v expression in the atrium. Velocity of unloaded shortening was determined at 15 degrees C in maximally activating Ca2+ solution (pCa 4.5) containing (in mmol/l) 7 EGTA, 1 free Mg2+, 4 MgATP, 14.5 creatine phosphate, and 20 imidazole (ionic strength 180 mmol/l, pH 7.0). Compared with the wild type (n = 10), the unloaded shortening velocity of MLC2v-expressing transgenic murine atrial cells (n = 10) was significantly greater (3.88 +/- 1.19 vs. 2.51 +/- 1.08 muscle lengths/s, P < 0.05). These results provide evidence that myosin light chain 2 regulates cross-bridge cycling rate. The faster rate of cycling in the presence of MLC2v suggests that the MLC2v isoform may contribute to the greater power-generating capabilities of the ventricle compared with the atrium.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Atrial Function / physiology*
  • Calcium / physiology
  • Gene Expression / physiology
  • Heart Ventricles
  • Kinetics
  • Mice
  • Mice, Transgenic / genetics
  • Myocardial Contraction / physiology
  • Myocardium / cytology
  • Myocardium / metabolism*
  • Myosin Light Chains / genetics
  • Myosin Light Chains / metabolism*
  • Time Factors
  • Transgenes / physiology


  • Myosin Light Chains
  • Calcium