Contractile responses of human internal mammary arteries
After cryostorage responses of human internal mammary arteries (IMA) to most contractile agonists are diminished. By contrast, contractile responses to endothelin-1 (ET-1) are enhanced.
In human internal mammary arteries ET-1 stimulates both ETA and ETB receptor subtypes. ETA receptors are located on the smooth muscle cells mediating contraction. ETB receptors are located predominantly on the luminal surface of endothelial cells mediating relaxation. Cryopreservation, however, damages the endothelium suggesting that the enhanced activity of endothelin in cryostored human IMA was due to loss of its relaxant component.
In addition, experiments with staurosporine, an inhibitor of protein kinase C , suggest that the freezing/thawing procedure enhances the activity of protein kinase C which increases the tonic contraction to ET-1 .