| Abstract: | A hydrostatic pressure of 60g/cm sq (0.85 psi) inhibits the accumulation of cAMP in cells isolated from the proliferative zone of chick-tibia epiphyseal cartilage. The following findings indicate that this effect is mediated by a translocation of calcium: (i) the pressure enhances the cellular uptake of radiocalcium; (ii) the pressure effect on cAMP can be simulated by the calcium-ionophore A23187; (iii) the effects of pressure and A23187 are non-additive; (iv) the pressure effect is not produced in the presence of ethylenebis-(oxyethylenenitrilo)-pressure effect is not produced in the presence of ethylenebis-(oxyethylenenitrilo)-tetraacetic-acid (EGTA); (v) the particulate adenyl cyclase activity of the proliferative zone is susceptible to non-competitive calcium inhibition. Throughout this study cells from the hypertrophic zone of the same epiphyses were used as controls. In these cells the calcium uptake was enhanced by pressure, but the cAMP level was not affected by pressure, A23187 or EGTA. This change in responsiveness, which accompanies the maturation of the cartilage cells, was shown to be due to a decrease in the calcium-inhibition of adenylate cyclase. |
