Inhibition of gastrin‐induced proliferation of AR4–2j cells by calcium channel antagonists

Abstract

The exact intracellular mechanisms by which gastrin enhances the proliferation of AR4–2J cells, a tumor pancreatic acinar cell line, are not precisely known. Calcium has long been considered as an intracellular signal involved in growth-regulatory control of many cell types. Moreover, Ca⁺⁺ channel blockers show growth-suppressing effects in most proliferating cells. In the present study, we analyzed the role of nifedipine, a voltage-dependent Ca⁺⁺ channel antagonist, on AR4–2J cells which possess well-defined voltage-dependent Ca⁺⁺ channels. The results showed that 10 nM gastrin induced a transient rise in intracellular calcium (Ca⁺⁺), followed by a sustained phase which was dependent upon a Ca⁺⁺ influx operating through nifedipine-dependent and-independent Ca⁺⁺ channels. Both influxes are necessary for reloading the agonist-sensitive Ca,⁺⁺ pools. In parallel, we demonstrated that nifedipine at doses of I μM and 3 μM preferentially blocked the increase in cell number elicited by 10 nM gastrin and 0.1 μM Bay K 8644, a Ca⁺⁺ channel agonist, suggesting that voltage-sensitive Ca⁺⁺ channel activity was required for gastrin-stimulated mitogenesis. Moreover, nifedipine had no effect on the proliferation of AR4–2J cells growing in serum-free medium, indicating that this drug did not simply exert a toxic effect. Therefore, Ca⁺⁺ influx through voltage-dependent Ca⁺⁺ channels might be an important initial step representing a component of a synergistic cooperation between different signal transduction pathways involved in gastrin-regulated growth.