Altered kinetics of contraction of mouse atrial myocytes expressing ventricular myosin regulatory light chain.
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.
Buck
S H
SH
Department of Pediatrics, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA. shbuck@facstaff.wisc.edu
Konyn
P J
PJ
Palermo
J
J
Robbins
J
J
Moss
R L
RL
D000818:Animals; D016275:Atrial Function / Q000502:physiology*; D002118:Calcium / Q000502:physiology; D015870:Gene Expression / Q000502:physiology; D006352:Heart Ventricles; D007700:Kinetics; D051379:Mice; D008822:Mice, Transgenic / Q000235:genetics; D009200:Myocardial Contraction / Q000502:physiology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D018994:Myosin Light Chains / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D019076:Transgenes / Q000502:physiology
D018994:Myosin Light Chains; D002118:Calcium