Hypoxic vasodilation in porcine coronary artery is preferentially inhibited by organ culture

Hypoxia (95% N₂-5%CO₂) elicits an endothelium-independent relaxation(45-80%) in freshly dissected porcine coronary arteries. Pairedartery rings cultured at 37°C in sterile DMEM (pH ~7.4) for 24 h contracted normally to KCl or 1 µM U-46619. However, relaxation inresponse to hypoxia was sharply attenuated compared with control (fresharteries or those stored at 4°C for 24 h). Hypoxicvasorelaxation in organ cultured vessels was reduced at both high andlow stimulation, indicating that both Ca²⁺-independent andCa²⁺-dependent components are altered. In contrast,relaxation to G-kinase (sodium nitroprusside) or A-kinase (forskolinand isoproterenol) activation was not significantly affected by organculture. Additionally, there was no difference in relaxation afterwashout of the stimulus, indicating that the inhibition is specific toacute hypoxia-induced relaxation. Simultaneous force and intracellularcalcium concentration ([Ca²⁺]_i) measurementsindicate the reduction in [Ca²⁺]_i concomitantwith hypoxia at low stimulus levels in these tissue is abolished byculture. Our results indicate that organ culture at 37°C specificallyattenuates hypoxic relaxation in vascular smooth muscle by alteringdynamics of [Ca²⁺]_i handling and decreasing aCa²⁺-independent component of relaxation. Thus organculture can be a novel tool for investigating the mechanisms ofhypoxia-induced vasodilation.