Dissociation of Ca2+ accumulation from protein release in calcium paradox: effect of barium

Experiments were undertaken to establish whether Ba2+ can substitute for Ca2+ in maintaining the structural and functional integrity of the glycocalyx. Adult rat hearts were perfused with Ca2+-free buffer at 37 degrees C, with and without added Ba2+. Ten minutes later Ba2+-free, Ca-containing medium was reintroduced. Hearts that had been perfused with Ca2+-free medium exhibited a distorted glycocalyx. On reperfusion with Ca2+-containing medium these hearts released protein (P less than 0.001), gained Ca2+ (P less than 0.001), and depleted their tissue stores of ATP (P less than 0.001) and CP (P less than 0.001). Hearts that had been perfused with Ca2+-free, Ba2+-containing medium retained an apparently intact glycocalyx. On reperfusion with Ca2+-containing. Ba2+-free medium they gained Ca2+ but did not lose protein. These results suggest that Ba2+ only partially replaces Ca2+ in maintaining the integrity of the cell surface. It is also concluded that the absence of protein release does not necessarily exclude the occurrence of severe changes in ionic permeability after cell injury.