Na+/H+ exchange in AR4-2J cells: stimulation by growth factors and pancreatic secretagogues

To study the relationships between activation of the Na+/H+ antiporter and gastrointestinal cell proliferation, we characterized this antiporter in a pancreatic cell line (AR4-2J). In the present study, the effects of mitogenic and non-mitogenic agents and of Na+/H+ exchange blocking agents on DNA synthesis are reported. Dialyzed fetal calf serum (FCS) (0-10%) increased amiloride-sensitive 22Na+ uptake in a concentration-dependent manner. There was a linear relationship between the increase in 22Na uptake and cell number when FCS was added in the 2-10% concentration range. Amiloride and analogs inhibited 3H-thymidine incorporation in the same concentration range as that with which they inhibited the Na+/H+ exchange. IC50 values were 1 microM for 5-(N-ethy-N-isopropyl)-amiloride (EIPA), 10 microM for 5-(N,N-dimethyl)-amiloride (DMA) and 0.1 mM for amiloride, respectively, indicating that activation of the Na+/H+ antiporter is necessary to initiate cell proliferation in AR4-2J cells. Maximal CCK9-induced 22Na uptake was 3.65 times the basal rate and was obtained at 0.1 nM. Maximal 22Na uptake triggered by unsulfated gastrin 17 was 2.51 times the basal rate and was obtained at 0.1 nM. The EC50s of CCK9 and gastrin in stimulating the 22Na uptake were similar at 1 pM. Maximal carbamylcholine-induced stimulation was observed at 0.1 mM and was 2.37 times greater than the basal rate. EC50 was 1 microM. In AR4-2J cells, the activity of the Na+/H+ exchanger seems to be directly involved in the control of cell proliferation. However, stimulation of this exchanger by stimulating factors that are not growth factors suggests that intracytoplasmic alkalinization could regulate other important metabolic processes which, as yet, are unknown.