The mechanism of cryoinjury: In vitro studies on human internal mammary arteries

1 The mechanism of cryoinjury was investigated in human internal mammary ar teries (IMB) by monitoring contractile responses to ET-1 and KCl. 2 For cryopreservation segments of TMA were equilibrated for 20 min with th e cryomedium (RPMI 1640 culture medium containing 1.8 M DMSO and 0.1 M sucr ose), frozen at a mean cooling rate of 1.3 degrees C min(-1) to - 70 degree s C and stored in liquid nitrogen. Before use, samples were thawed slowly a nd the cryomedium removed by dilution. 3 Compared to unfrozen controls, ET-1 stimulated frozen/thawed TMA with sim ilar efficacy but at 3 fold lower concentrations (P < 0.001). Addition of E T-1 (100 nM) induced maximal contraction of unfrozen IMA within 10 min, dec lining thereafter to 25% after 90 min. In frozen:thawed IMA the ET-1-induce d contraction was sustained but could be reversed if protein kinase C was b locked by staurosporine (100 nM). Responses to ET-1 of cryostored IMA were 5 fold more susceptible to blockade by nifedipine than those of controls. 4 After cryostorage the efficacy of KCl was diminished to 40% (P < 0.05) an d the KCl curve was shifted to the left (2 fold, P < 0.001). In both unfroz en and cryostored IMA the KCl (60 mM) effect was sustained and equally susc eptible to nifedipine. 5 It is suggested that the smooth muscle cell of IMA is receptive to physic al forces which occur during cryopreservation. These forces modify transmem brane signal transduction and intracellular pathways, that are common to ph armacological agonists thereby changing vascular responses to several contr actile agonists after thawing.