BOVINE LENS EPITHELIUM - SUITABLE MODEL FOR STUDYING GROWTH-CONTROL MECHANISMS - C6-SUBSTITUTED PURINES INHIBIT CELL FLATTENING AND GROWTH-STIMULATION OF G0 CELLS

1. 1. The resting lens epithelium of adult bovines has been used for the study of early events during stimulation to mitotic growth in primary culture. This system offers special advantages, since it consists of a pure population of 'anchorage dependent' epithelial cells with more than 99% of the cells in G0. 2. 2. Retraction of the cell sheet as well as respreading and cell flattening are characteristic phenomena of locomotion preceding the inception of DNA synthesis in primary culture. 3. 3. Sheet retraction has been characterized as an active, ATP-dependent process requiring both intact microfilaments and extracellular calcium. 4. 4. The early phase of respreading is dependent on neither intact microfilaments nor microtubules, but is specifically inhibited by adenine, hypoxanthine, guanine, adenosine, AMP and cAMP. Calcium uptake experiments reveal that these purine derivatives reduce the uptake of extracellular calcium which is suggested to be the virtual primary mitotic stimulator for resting lens cells. 5. 5. A conspicuous correlation does exist between the calcium depressing specificity of the purine derivatives, their well known capacity to depress the level of cellular phosphoribosylpyrophosphate (PRPP) and their ability to retard cell flattening. 6. 6. The calcium-depressing action of the purines has been suggested to be partially responsible for their PRPP-depressing capacity and it is concluded that both calcium and PRPP might be involved in the activation process of 'anchorage dependent' resting lens cells. © 1979.