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Am J Physiol Heart Circ Physiol 276: H1167-H1171, 1999;
0363-6135/99 $5.00
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Vol. 276, Issue 4, H1167-H1171, April 1999

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

Scott H. Buck1, Patrick J. Konyn1, Joseph Palermo2, Jeffrey Robbins2, and Richard L. Moss3

Departments of 1 Pediatrics and 3 Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706; and 2 Division of Molecular Cardiovascular Biology, Children's Hospital Research Foundation, Cincinnati, Ohio 45229

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°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.

myofilaments; isoforms; shortening velocity; transgenic


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