Investigating the relaxation rate, following diazo-2 photolysis, of a skinned trabecular preparation from guinea-pig hypertrophied left ventricle

Cardiac hypertrophy in the guinea-pig is not accompanied by a large shift i n the expression of the predominant isoform of myosin in the left ventricle ; however, in this species, thin filament proteins do change. We examined t he relaxation, following laser flash photolysis of the photolabile caged Ca 2+ chelator diazo-2, of a skinned trabecular preparation from the left vent ricle of guineapigs that had undergone abdominal aortic banding. Sham-opera ted animals were used as controls; no guinea-pigs showed any signs of heart failure. We report that mild cardiac hypertrophy does not affect the relax ation rate of Triton-skinned trabeculae from the guinea-pig. However, there was a 35% reduction in the maximum force generated by trabeculae from the left ventricle of the abdominal aortic-banded animals. Additionally, altera tions in key troponin subunits occur in the left ventricle of guinea-pigs w ith mild hypertrophy We conclude that the thin filament protein changes do not influence trabecular relaxation rates, even though they probably affect maximal force generation. The cellular membrane systems of the intact guin ea-pig heart, which were not a factor in this present study, appear to have an important role in the altered cardiac relaxation rates seen in hypertro phy.