Pharmacological evaluation of the role of cytochrome P450 in intracellular calcium signalling in rat pancreatic acinar cells

We have investigated whether the cytochrome P450 system is involved in Ca 2+ signalling in rat pancreatic acinar cells. Intracellular free [Ca 2+ ] ([Ca 2+ ] i ) was measured in collagenase‐isolated cells using fura‐2 microspectrofluorimetry and imaging. The imidazole P450 inhibitor ketoconazole (5–50 μ M ) inhibited [Ca 2+ ] i oscillations induced by cholecystokinin octapeptide (CCK). However, ketoconazole also raised baseline [Ca 2+ ] i when applied in the absence of CCK. These effects were mimicked by 5–50 μ M SKF96365, an imidazole widely used as an inhibitor of Ca 2+ entry. The non‐imidazole P450 inhibitor proadifen (SKF525A) inhibited CCK‐induced [Ca 2+ ] i oscillations at a concentration of 10–50 μ M . Proadifen alone caused intracellular Ca 2+ release at 25 or 50 μ M , but not at 10 μ M . Octadecynoic acid and 1‐aminobenzotriazole, structurally‐unrelated non‐imidazole P450 inhibitors, did not alter baseline [Ca 2+ ] i or CCK‐evoked oscillations. We compared cumulative CCK dose‐response relationship in control cells and in cells where P450 had been induced by prior injection of animals with β‐naphthoflavone. Only minor differences were apparent, with induced cells showing some decrease in responsiveness at moderate and higher concentration of CCK (30 p M –3 n M ). Direct assessment of depletion‐activated Ca 2+ entry showed no clear differences between control and induced cells. In conclusion, we could find no compelling evidence for a role of P450 in controlling Ca 2+ signalling generally, or Ca 2+ entry in particular, in pancreatic acinar cells. Induction of P450 is therefore probably toxic to acinar cells via a Ca 2+ ‐independent mechanism.British Journal of Pharmacology (2000) 131 , 761–771; doi: 10.1038/sj.bjp.0703631