期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 277, 期 6, 页码 4422-4427出版社
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M111047200
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资金
- NHLBI NIH HHS [HL64137] Funding Source: Medline
The magnitude of agonist-induced Ca2+ sensitization of force is tissue-dependent, but an explanation for this diversity is unknown. Ca2+ sensitization is thought to involve a G-protein-mediated inhibition of myosin light chain phosphatase activity by phosphorylation of the myosin-targeting subunit (MYPT). The MYPT has two isoforms that differ by a central insert, which lies near this phosphorylation site. Expression of MYPT isoforms is both developmentally regulated and tissue-specific. We hypothesized that the presence or absence of the central insert determines the magnitude of agonist-induced Ca2+ sensitization. Throughout development, the chicken aorta exclusively expresses the splice-in MYPT isoform, and guanosine 5'-O-(thiotriphosphate) (GTPgammas) produces a significant force enhancement. Early during development, the chicken gizzard expresses the splice-in MYPT isoform, and GTPgammaS produced a Ca2+ sensitization. In the gizzard coincident with the shift in expression from the splice-in to splice-out MYPT isoform, GTPgammaS no longer produced force enhancement. In addition, adenosine 5'-O-(thiotriphosphate) (ATPgammaS) phosphorylated only adult gizzard tissue, the only tissue that did not demonstrate a Ca2+ sensitization. These results suggest that the relative expression of splice-in/splice-out MYPT isoforms determines the magnitude of agonist-induced force enhancement and that MYPT phosphorylation is not required for Ca2+ sensitization.
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