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Ca 2+ ‐independent hypoxic vasorelaxation in porcine coronary artery
Author(s) -
Gu Min,
Thorne George D.,
Wardle Robert L.,
Ishida Yukisato,
Paul Richard J.
Publication year - 2005
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.2004.073692
Subject(s) - gtp' , myosin , myosin light chain kinase , egta , biophysics , chemistry , hypoxia (environmental) , phosphorylation , myosin light chain phosphatase , medicine , endocrinology , biology , biochemistry , calcium , oxygen , enzyme , organic chemistry
To demonstrate a Ca 2+ ‐independent component of hypoxic vasorelaxation and to investigate its mechanism, we utilized permeabilized porcine coronary arteries, in which [Ca 2+ ] could be clamped. Arteries permeabilized with β‐escin developed maximum force in response to free Ca 2+ (6.6 μ m ), concomitant with a parallel increase in myosin regulatory light chain phosphorylation (MRLC‐P i ), from 0.183 ± 0.023 to 0.353 ± 0.019 MRLC‐P i (total light chain) −1 . Hypoxia resulted in a significant decrease in both force (–31.9 ± 4.1% prior developed force) and MRLC‐P i (from 0.353 to 0.280 ± 0.023), despite constant [Ca 2+ ] buffered by EGTA (4 m m ). Forces developed in response to Ca 2+ (6.6 μ m ), Ca 2+ (0.2 μ m ) + GTPγS (1 m m ), or in the absence of Ca 2+ after treatment with ATPγS (1 m m ), were of similar magnitude. Hypoxia also relaxed GTPγS contractures but importantly, arteries could not be relaxed after treatment with ATPγS. Permeabilization with Triton X‐100 for 60 min also abolished hypoxic relaxation. The blocking of hypoxic relaxation after ATPγS suggests that this Ca 2+ ‐independent mechanism(s) may operate through alteration of MRLC‐P i or of phosphorylation of the myosin binding subunit of myosin light chain phosphatase. Treatment with the Rho kinase inhibitor Y27632 (1 μ m ) relaxed GTPγS and Ca 2+ contractures; but the latter required a higher concentration (10 μ m ) for consistent relaxation. Relaxations to N 2 and/or Y27632 averaged 35% and were not additive or dependent on order. Our data suggest that the GTP‐mediated, Rho kinase‐coupled pathway merits further investigation as a potential site of this novel, Ca 2+ ‐independent O 2 ‐sensing mechanism. Importantly, these results unambiguously show that hypoxia‐induced vasorelaxation can occur in permeabilized arteries where the Ca 2+ is clamped at a constant value.