Fluorescence lifetime of actin in the familial hypertrophic cardiomyopathy transgenic heart.

Abstract

Clinical studies have revealed that the D166V mutation in the ventricular myosin regulatory light chain (RLC) can cause a malignant phenotype of familial hypertrophic cardiomyopathy (FHC). It has been proposed that RLC induced FHC in the heart originates at the level of the myosin cross-bridge due to alterations in the rates of cross-bridge cycling. In this report, we examine whether the environment of an active cross-bridge in cardiac myofibrils from transgenic (Tg) mice is altered by the D166V mutation in RLC. The cross-bridge environment was monitored by tracking the fluorescence lifetime (tau) of Alexa488-phalloidin-labeled actin. The fluorescence lifetime is the average rate of decay of a fluorescent species from the excited state, which strongly depends on various environmental factors. We observed that the lifetime was high when cross-bridges were bound to actin and low when they were dissociated from it. The lifetime was measured every 50 ms from the center half of the I-band during 60 s of rigor, relaxation and contraction of muscle. We found no differences between lifetimes of Tg-WT and Tg-D166V muscle during rigor, relaxation and contraction. The duty ratio expressed as a fraction of time that cross-bridges spend attached to the thin filaments during isometric contraction was similar in Tg-WT and Tg-D166V muscles. Since independent measurements showed a large decrease in the cross-bridge turnover rate in Tg-D166V muscle compared to Tg-WT, the fact that the duty cycle remains constant suggests that the D166V mutation of RLC causes a decrease in the rate of cross-bridge attachment to actin.

• Authors: P Mettikolla, R Luchowski, I Gryczynski, Z Gryczynski, D Szczesna-Cordary, J Borejdo
• Journal: Biochemistry (Biochemistry) Vol. 48 Issue 6 Pg. 1264-71 (Feb 17 2009) ISSN: 1520-4995 [Electronic] United States
• PMID: 19159226 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Actins
• Phalloidine

Topics

• Actin Cytoskeleton (metabolism)
• Actins (metabolism)
• Animals
• Cardiomyopathy, Hypertrophic, Familial (physiopathology)
• Fluorescence
• Heart (physiopathology)
• Mice
• Mice, Transgenic
• Myocardial Contraction (physiology)
• Myofibrils (pathology)
• Phalloidine (metabolism)
• Rigor Mortis (physiopathology)
• Time Factors