Nongenomic mechanism of glucocorticoid inhibition of bradykinin-induced calcium influx in PC12 cells: Possible involvement of protein kinase C

Many stimulants, including bradykinin (BK), can induce increase in [Ca²⁺]_i in PC12 cells. Bradykinin induces an increase in [Ca²⁺]_i via intracellular Ca²⁺ release and extracellular Ca²⁺ influx through the transduction of G protein, but not through voltage-sensitive calcium channels. In this experiment, We analyzed how corticosterone (Cort) influences BK-induced intracellular Ca²⁺ release and extracellular Ca²⁺ influx, and further studied the mechanism of glucocorticoid's action. To dissociate the intracellular Ca²⁺ release and extracellular Ca²⁺ influx induced by BK, the Ca²⁺-free/Ca²⁺- reintroduction protocol was used. The results were as follows: (1) The Ca²⁺ influx induced by BK could be rapidly inhibited by Cort, but intracellular Ca²⁺ release could not be affected significantly. (2) The inhibitory effect of Cort-BSA (BSA -conjugated Cort) on Ca²⁺ influx induced by BK was the same as the effect of free Cort. (3) Protein kinase C (PKC) activator (phorbol 12-myristate 13-acetate) could mimic and PKC inhibitor Gö6976 could reverse the inhibitory effect of Cort. (4) There was no inhibitory effect of Cort on Ca²⁺ influx induced by BK when pretreated with pertussis toxin. The results suggested, for the first time, that Cort might act via a putative membrane receptor and inhibit the Ca²⁺ influx induced by BK through the pertussis toxin -sensitive G protein-PKC pathway.