• Hypoxic constriction of porcine coronary arteries is independent of extracellular Ca²⁺ influx and intracellular Ca²⁺ release from the sarcoplasmic reticulum.
• The hypoxic response requires endothelium-derived nitric oxide (NO) and activation of soluble guanylyl cyclase (sGC) in vascular smooth muscle cells.
• Hypoxic contraction is mediated by increased calcium sensitivity via inhibition of myosin light chain phosphatase (MLCP) activity.
• Calcium sensitization, rather than changes in intracellular calcium levels, is the key determinant of hypoxic coronary artery constriction.