[Ultracytochemical study of Ca++-ATPase activity in rabbit trabecular meshwork]

Cytochemical localization of Ca++-ATPase activity in endothelial cells of rabbit trabecular meshwork was studied by the method of Ando et al. Ca++-ATPase activity was localized on the plasma membrane, mitochondria, endoplasmic reticulum, and the basal cytoplasmic matrix, which includes the actin filament bundles beneath the basal plasma membrane. Ca++-ATPase activity associated with membranous organelles was considerably reduced by quercetin, an inhibitor of ATP dependent Ca++-transport. Changes in the concentrations of Ca (1-10mM) greatly influenced the activity of the cytoplasmic matrix. The most intense activity was obtained at 1mM Ca. These findings suggest that Ca++-ATPase of mitochondria and sarcoplasmic reticulum is related to the active uptake of Ca++ by these structures, and the reaction within actin filament bundles may reflect actomyosin ATPase activity. The function of cAMP and actomyosin ATPase reaction may be to provide contractility of the trabecular meshwork resulting in an alteration of outflow resistance of aqueous humor drainage.