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MUSCLE CELL BIOLOGY AND CELL MOTILITY
1Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden; 2Department of Thoracic Surgery, University of Lund, Lund, Sweden
Submitted 27 October 2006 ; accepted in final form 2 July 2007
Blebbistatin is a powerful inhibitor of actin-myosin interaction in isolated contractile proteins. To examine whether blebbistatin acts in a similar manner in the organized contractile system of striated muscle, the effects of blebbistatin on contraction of cardiac tissue from mouse were studied. The contraction of paced intact papillary muscle preparations and shortening of isolated cardiomyocytes were inhibited by blebbistatin with inhibitory constants in the micromolar range (1.3–2.8 µM). The inhibition constants are similar to those previously reported for isolated cardiac myosin subfragments showing that blebbistatin action is similar in filamentous myosin of the cardiac contractile apparatus and isolated proteins. The inhibition was not associated with alterations in action potential duration or decreased influx through L-type Ca2+ channels. Experiments on permeabilized cardiac muscle preparations showed that the inhibition was not due to alterations in Ca2+ sensitivity of the contractile filaments. The maximal shortening velocity was not affected by 1 µM blebbistatin. In conclusion, we show that blebbistatin is an inhibitor of the actin-myosin interaction in the organized contractile system of cardiac muscle and that its action is not due to effects on the Ca2+ influx and activation systems.
heart; electrophysiology; permeabilized muscle
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