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A.T. Read, D.W. H. Chan, C.R. Ethier; Structural Changes Following Latrunculin–B Perfusion in Human Eyes . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2086.
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Purpose: Latrunculin–B (Lat–B), an F–actin–disrupting agent, reversibly increases outflow facility in monkey eyes. Here we investigated its effects on facility and ultrastructure in human eyes in order to try to more clearly determine how alterations in F–actin might result in increased outflow facility. Methods: Paired ostensibly normal human eyes (average post mortem time = 22.9 hrs) were perfused at 8 mmHg and had outflow facility measured before and after anterior chamber exchange with 1.0 µM Lat–B. Eyes were then fixed at 8 mmHg, adjusting fixation duration so as to equalize fixative volume between fellow eyes of a pair and hence compensate for fixative–induced pore formation in the inner wall of Schlemm’s canal. Using standard techniques, inner wall pores were counted and measured by scanning electron microscopy (SEM), and trabecular meshwork morphology was examined by transmission electron microscopy (TEM). Results: Lat–B increased facility by 73 ± 18% (mean ± SEM; n = 11 pairs; p = 0.002) 100 minutes after administration. By scanning EM, the density and size of inner wall pores increased (mean change +108% and +54%, respectively), with most of the increase due to a higher frequency of pores on cell borders (324% mean increase). Facility increase was not correlated with increase in size or density of inner wall pores. By transmission EM, some distension of juxtacanalicular tissue and inner wall of Schlemm’s canal was observed, although the extent of this distension was not remarkable. No loss of Schlemm’s canal inner wall cells was observed. Conclusions: The most striking ultrastructural change due to Lat–B was a focal loss of cell–cell attachment between Schlemm’s canal endothelial cells, as visualized by SEM. This increase in inner wall porosity was not notable when viewed by TEM, likely due to the fact that TEM sections sample only a very small fraction of the inner wall. Lat–B also slightly "loosened" the trabecular meshwork, as has been reported for other actin–disrupting agents. Because inner wall pore density changes do not seem to be correlated with facility changes, the mode of action by which Lat–B increases facility remains unclear.
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