8-isoprostaglandin E(2) activates Ca(2+)-dependent K(+) current via cyclic AMP signaling pathway in murine renal artery

The inhibitory pathway of 8-isoprostaglandin E₂ was investigated in murine renal arterial smooth muscle. K⁺ current was augmented in a concentration-dependent fashion, with an average increase of 123 ± 28% (n = 6) following application of 10^− 5 M 8-isoPGE₂. This augmentation was observed in the presence of 4-aminopyridine (4-AP, 10^− 3 M) but not that of charybdotoxin (ChTx, 10^− 7 M). Fluorimetric recordings showed marked concentration-dependent increase of cytosolic Ca²⁺ levels by 8-isoPGE₂, while an enzyme-linked immunosorbent assay (ELISA)-based cyclic AMP assay showed increased cAMP levels by 10^− 7 M 8-isoPGE₂ challenge. The isoprostane-induced augmentation was prevented by the ryanodine receptor blocker ruthenium red (10^− 5 M) or the adenylate cyclase blocker SQ 22536 (10^− 4 M). The protein kinase A (PKA) inhibitor H89 (10^− 5 M) inhibited resting K⁺ currents (78 ± 5%, n = 5) but did not prevent 8-isoPGE₂ from augmenting the remaining K⁺ current. We conclude that 8-isoPGE₂ enhances Ca²⁺-dependent K⁺ currents in murine renal artery through a cAMP-dependent pathway which may involve internally sequestered Ca²⁺.