Alkalinization stimulates Ca2+-dependent spreading during the activation of resting lens epithelial cells in primary culture.

Lens epithelium, when attached to its natural substratum, the lens capsule, can be maintained in culture for more than 2 weeks in a simple HEPES- and EDTA-buffered salt solution (HBS). In HBS, the epithelium shows the same characteristic phenomena of locomotion, initial retraction and respreading which in MEM plus serum precedes the inception of DNA synthesis. These phenomena have been shown to be dependent on extracellular Ca2+. 0.05 mM Ca2+ is necessary for maintaining cell-to-cell contacts of the in vivo epithelium. Higher concentrations of Ca2+ cause the epithelium to retract initially. In contrast, Mg2+ greatly favours cell-substratum interactions leading to the formation of lamellopodia and an initial spreading of the epithelium. After some hours in culture the epithelium changes markedly in response to extracellular Ca2+ and Mg2+; it respreads and flattens in the presence of Ca2+, while Mg2+ becomes less effective in maintaining cell-to-substratum contacts. Mg2+-dependent initial spreading is promoted at pH values near 7.0 but the Ca2+-dependent respreading requires an alkalinization of the salt solution.