Differential scanning microcalorimetry showed that calorimetric enthalpy of melting of purified G-actin from canine myocardium is decreased in L-thyroxin-induced cardiomyopathy. By contrast, in athyroid cardiomyopathy this parameter increases almost 2-fold mainly due to the increase in excess heat capacity in a low-temperature region of the thermogram caused by melting of the small domain in the monomer. The pathological process in both cases is accompanied by contractility disturbances.
Key Words: G-actin," thermodynamics," athyroid cardiomyopathy," L-thyroxin cardiomyopathyIt was previously established that 2-3-month-long cardiac insufficiency caused by L-thyroxin-induced (LTC) and athyroid (ATC) cardiomyopathy (or myocardial dystrophy according to G. F. Lang) strongly impairs polymerization of actin in human or animal myocardium [9]. According to circular dichroism data, the conformation of G-and F-actins changes drastically [3]; hybrid actomyosin containing actin from the post mortem myocardium of a patient dead from cardiac insufficiency [8] superprecipitates (contracts [7]) much more weaker than actomyosin containing normal actin.Our aim was to study thermodynamic parameters of melting of G-actin from canine myocardium in LTC and ATC.
MATERIALS AND METHODSExperiments were carried out on 16 male mongrel dogs: control animals (n=5) and dogs with LTC (n=6) and ATC (n=5). The dogs were maintained under vivarium conditions on a standard ration. The animals were euthanized under hexenal narcosis.
Differential scanning microcalorimetry was used to determine changes in enthalpy, entropy, and free energy of melting of purified myocardial fibrillar (F) actin from normal dogs and dogs with 2-3-month L-thyroxin-induced and athyreotic cardiomyopathy. Polymerization of globular (G) actin stabilizes protomer structure in both pathologies. However, the conformational changes in actin monomer caused by L-thyroxin-induced and, especially, by athyreotic cardiomyopathy decrease the free energy of the bonds between protomers in the synthesized F-actin. Binding energy between actin protomers modified in athyreotic cardiomyopathy (-12 kJ/mol) is 4 times below the control value (.-48.7 kJ/mol), while in L-thyroxininduced cardiomyopathy it little differs from the normal value (-40.8 kJ/mol).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.