ISSN:
0002-9106
Keywords:
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Medicine
Notes:
Myocytes in adult rabbit ventricle express an α and a β form of myosin heavy chain (MHC). The α-MHC distribution detected with indirect immunofluorescence has been found in different proportions in adjacent myocytes producing a mosaic staining pattern. The basis for cell-specific expression of the α-MHC isoform is not known. Since thyroid hormone is a major regulator of myosin gene expression, we varied the plasma thyroid level and followed the α-MHC content within a population of myocytes. Ventricular myocytes were induced to become 100% β-MHC by placing the rabbits on a 0.15% propylthiouracil diet for 70 days. L-triiodothyronine (LT3) over a dose range of 1 to 10 μg/kg/day was delivered by an osmotic minipump for 5 days, with actual serum levels confirmed by LT3 radioimmunoassay to be in the range of from 115 to 1,230 ng/dl. The amount of α-MHC that returned was estimated in randomly selected cells by measuring the relative intensity of the fluorescence-tagged secondary antibody. The normal mosaic pattern of α-MHC expression in the left ventricle returned with an LT3 dose of 2-5 μg/kg/day. The first myocytes to express α-MHC were in the subepicardium and did so at a LT3 serum level of 115 of ng/dl. All myocytes of the ventricular wall expressed α-MHC at serum levels above 1,230 ng/dl. These data are interpreted to show that the variation of myosin isoform content seen in the adult heart is indicative of heterogeneity of thyroid sensitivity, with the threshold for serum LT3 being between 115 and 370 ng/dl.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/aja.1001850408
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