Ca2+-independent hypoxic vasorelaxation in porcine coronary artery.

Abstract

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 beta-escin developed maximum force in response to free Ca(2+) (6.6 microm), 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 mm). Forces developed in response to Ca(2+) (6.6 microm), Ca(2+) (0.2 microm) + GTPgammaS (1 mM), or in the absence of Ca(2+) after treatment with ATPgammaS (1 mM), were of similar magnitude. Hypoxia also relaxed GTPgammaS contractures but importantly, arteries could not be relaxed after treatment with ATPgammaS. Permeabilization with Triton X-100 for 60 min also abolished hypoxic relaxation. The blocking of hypoxic relaxation after ATPgammaS 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 microm) relaxed GTPgammaS and Ca(2+) contractures; but the latter required a higher concentration (10 microm) 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.

• Authors: Min Gu, George D Thorne, Robert L Wardle, Yukisato Ishida, Richard J Paul
• Journal: The Journal of physiology (J Physiol) Vol. 562 Issue Pt 3 Pg. 839-46 (Feb 01 2005) ISSN: 0022-3751 [Print] England
• PMID: 15564284 (Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• adenosine 5'-O-(3-thiotriphosphate)
• Guanosine 5'-O-(3-Thiotriphosphate)
• Adenosine Triphosphate
• Oxygen
• Calcium

Topics

• Adenosine Triphosphate (analogs & derivatives, metabolism)
• Animals
• Calcium (metabolism)
• Cell Hypoxia (physiology)
• Cell Membrane Permeability (physiology)
• Coronary Vessels (physiology)
• Guanosine 5'-O-(3-Thiotriphosphate) (metabolism)
• In Vitro Techniques
• Muscle Contraction (physiology)
• Muscle, Smooth, Vascular (physiology)
• Oxygen (metabolism)
• Swine
• Vasodilation (physiology)