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Am J Physiol Heart Circ Physiol 283: H642-H649, 2002. First published April 25, 2002; doi:10.1152/ajpheart.00890.2001
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Vol. 283, Issue 2, H642-H649, August 2002

Ca2+ activation and tension cost in myofilaments from mouse hearts ectopically expressing enteric gamma -actin

Anne F. Martin1,*, Ronald M. Phillips1,*, Ajit Kumar2, Kelly Crawford2, Zainab Abbas2, James L. Lessard2, Pieter de Tombe1, and R. John Solaro1

1 Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois 60612; and 2 Children's Hospital Research Foundation, Cincinnati, Ohio 45229

To determine the significance of actin isoforms in chemomechanical coupling, we compared tension and ATPase rate in heart myofilaments from nontransgenic (NTG) and transgenic (TG) mice in which enteric gamma -actin replaced >95% of the cardiac alpha -actin. Enteric gamma -actin was expressed against three backgrounds: mice expressing cardiac alpha -actin, heterozygous null cardiac alpha -actin mice, and homozygous null cardiac alpha -actin mice. There were no differences in maximum Ca2+ activated tension or maximum rate of tension redevelopment after a quick release and rapid restretch protocol between TG and NTG skinned fiber bundles. However, compared with NTG controls, Ca2+ sensitivity of tension was significantly decreased and economy of tension development was significantly increased in myofilaments from all TG hearts. Shifts in myosin isoform population could not fully account for this increase in the economy of force production of TG myofilaments. Our results indicate that an exchange of cardiac alpha -actin with an actin isoform differing in only five amino acids has a significant impact on both Ca2+ regulation of cardiac myofilaments and the cross-bridge cycling rate.

cross bridge; myosin isoforms; energy coupling

* A. F. Martin and R. M. Phillips contributed equally to this study.




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