Protamine augments stretch induced calcium increase in vascular endothelium

1 Human umbilical vein endothelial cells cultured on a transparent silicone chamber were subjected to a short stretch pulse (ca. 1 s, 5-25% stretch) o f their substrate and following increases in intracellular Ca2+ concentrati on ([Ca2+](i)) were measured by fluorescence intensity ratiometry using fur a-2. 2 In response to mechanical stretch, the cells in HEPES buffered saline exh ibited a Ca2+ transient in a dose dependent way. The response was completel y dependent on external Ca2+ and inhibited by gadolinium (Gd3+), suggesting that it was mediated by the activation of a stretch activated cation chann el (SACatC). 3 Interestingly, the stretch induced Ca2+ transient was significantly augme nted in the presence of basic polypeptide, protamine. This augmented Ca2+ r esponse was inhibited neither by Gd3+ nor by the deprivation of external Ca 2+, indicating that the SACatC is not responsible for this phenomenon. 4 In contrast, this augmentation was inhibited by depletion of intracellula r Ca2+ stores with thapsigargin or by the pretreatment with phospholipase i nhibitors such as U73122 and manoalide. 5 These results suggest the presence of a metabotropic mechanoreceptor dist inct from the SACatC in vascular endothelium. This augmented [Ca2+](i) incr ease may contribute to the vasodilating response induced by protamine durin g heparin neutralization in cardiac surgery.