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Ca 2+ ‐desensitizing hypoxic vasorelaxation: pivotal role for the myosin binding subunit of myosin phosphatase (MYPT1) in porcine coronary artery
Author(s) -
Wardle Robert L.,
Gu Min,
Ishida Yukisato,
Paul Richard J.
Publication year - 2006
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2005.104083
Subject(s) - myosin light chain phosphatase , dephosphorylation , hypoxia (environmental) , myosin , biology , phosphatase , phosphorylation , kinase , rho associated protein kinase , myosin light chain kinase , protein subunit , microbiology and biotechnology , anatomy , chemistry , biochemistry , oxygen , organic chemistry , gene
Acute hypoxia dilates most systemic arteries leading to increased tissue perfusion. We showed that at high stimulus conditions, porcine coronary artery was relaxed by hypoxia without a change in [Ca 2+ ] i . This ‘Ca 2+ ‐desensitizing hypoxic relaxation’ was validated in permeabilized porcine coronary artery smooth muscle (PCASM) in which hypoxia decreased force and myosin regulatory light chain phosphorylation (p‐MRLC) despite fixed [Ca 2+ ]. Rho kinase‐dependent phosphorylation of MYPT1 (p‐MYPT1) is associated with decreased MRLC phosphatase (MLCP) activity, and increased Ca 2+ sensitivity of both p‐MRLC and force. We tested the hypothesis that hypoxia induces Ca 2+ ‐desensitizing hypoxic relaxation via dephosphorylation of p‐MYPT1, consequently increasing MLCP activity and thus decreasing p‐MRLC. α‐Toxin‐permeabilized PCASM pretreated with ATPγS did not relax in response to hypoxia. Moreover, when MRLC but not MYPT1 was protected from ATPγS thiophosphorylation by the MRLC kinase inhibitor ML7 (300 μ m ), hypoxia remained ineffective. In contrast, hypoxic relaxation was preserved with further addition of the Rho kinase inhibitor Y27632 (1 μ m ), to attenuate thiophosphorylation of MYPT1. Importantly, measurements of p‐MRLC, and p‐MYPT1 at T696 and T853 (human sequence) paralleled that of force. We conclude that Ca 2+ ‐desensitizing hypoxic relaxation requires dephosphorylation of p‐MYPT1. Moreover, no kinases, other then those inhibited by ML7 and Y27632, nor their associated phosphoproteins can be involved in Ca 2+ ‐desensitizing hypoxic relaxation.