CALCIUM ENHANCES ACANTHAMOEBA-POLYPHAGA BINDING TO EXTRACELLULAR-MATRIX PROTEINS

Purpose. To characterize better the ameba-host interactions that may b e involved with the pathogenesis of Acanthamoeba keratitis, the role o f calcium (Ca2+) on the binding of Acanthamoeba polyphaga to extracell ular matrix proteins was examined in vitro. Methods. The binding of a metabolically labeled A. polyphaga (CDC:0187:1) isolate from a case of human keratitis to collagen type IV, laminin, and fibronectin was ass essed through a range of calcium concentrations in the external fluid. Binding to collagen IV was studied in detail, with and without other divalent cations and calcium channel modulators. Results. Calcium incr eased binding in a dose-dependent manner, with significant effects at 0.1 to 1.0 mu M and near-maximal effects at 1 to 100 mu M, depending u pon the matrix protein. Magnesium alone had no effect on ameba binding to collagen IV but suppressed the action of calcium. Strontium enhanc ed ameba binding, with maximal effect at 100 mu M. The calcium channel antagonists nifedipine and diltiazem-HCl and a calcium channel activa tor, Bay-K8644, had no effect on the action of calcium. However, the i norganic calcium antagonists, lanthanum and cobalt, suppressed the eff ect of calcium. Conclusion. Low concentrations of calcium enhance the adhesion of A. polyphaga to extracellular matrix proteins. It remains uncertain whether calcium acts intracellularly or at the cell surface.