Effect of phalloidin on structure and permeability of rete capillaries in the normal and hypoxic state

The effects of 10(-6) M phalloidin on reperfusion-injured blood capillary structure and permeability were studied in the countercurrent perfused rete mirabile of the eel swim bladder. In the normal rete, the addition of phalloidin to the perfusion medium did not induce morphological or functional changes. When flow was arrested for 30 minutes, during which time the capillaries were exposed to inhibitors of ATP generation, and flow was then resumed with an oxygenated medium, cell membrane blebs and vacuolization, mitochondrial swelling, pericyte shrinkage, and interstitial space edema were observed. The permeability coefficients for labeled albumin, sucrose, and sodium increased to three to four times baseline values, whereas the permeability to water was not significantly modified. When the same protocol was repeated with phalloidin present in the medium throughout the experiment, the structural integrity of the endothelial cells was completely preserved and pericyte shrinkage was abolished, but interstitial space edema still occurred. The permeability to albumin, sucrose, and sodium increased only to 1.5 times baseline values, a significantly decreased increment in comparison with the experiments performed without phalloidin. We concluded that although phalloidin does not improve the capillary barrier of the normal rete, it provides protection against the structural and functional damage induced by hypoxia and reperfusion.