Protamine augments stretch induced calcium increase in vascular endothelium

Human umbilical vein endothelial cells cultured on a transparent silicone chamber were subjected to a short stretch pulse ( ca . 1 s, 5 – 25% stretch) of their substrate and following increases in intracellular Ca 2+ concentration ([Ca 2+ ] i ) were measured by fluorescence intensity ratiometry using fura‐2. In response to mechanical stretch, the cells in HEPES buffered saline exhibited a Ca 2+ transient in a dose dependent way. The response was completely dependent on external Ca 2+ and inhibited by gadolinium (Gd 3+ ), suggesting that it was mediated by the activation of a stretch activated cation channel (SACatC). Interestingly, the stretch induced Ca 2+ transient was significantly augmented in the presence of basic polypeptide, protamine. This augmented Ca 2+ response was inhibited neither by Gd 3+ nor by the deprivation of external Ca 2+ , indicating that the SACatC is not responsible for this phenomenon. In contrast, this augmentation was inhibited by depletion of intracellular Ca 2+ stores with thapsigargin or by the pretreatment with phospholipase inhibitors such as U73122 and manoalide. These results suggest the presence of a metabotropic mechanoreceptor distinct from the SACatC in vascular endothelium. This augmented [Ca 2+ ] i increase may contribute to the vasodilating response induced by protamine during heparin neutralization in cardiac surgery.British Journal of Pharmacology (2001) 134 , 1403–1410; doi: 10.1038/sj.bjp.0704386