PGE2 action in human coronary artery smooth muscle: role of potassium channels and signaling cross-talk.

Cyclic AMP-stimulating agents are powerful vasodilators, but our knowledge of the signal transduction mechanisms of these agents, particularly in human arteries, is limited. We now report direct molecular effects of prostaglandin E(2) (PGE(2)) on cultured human coronary artery smooth muscle cells (HCASMC). Patch-clamp studies revealed that 10 microM PGE(2) opens a high-conductance (approximately 200 pS), calcium-stimulated potassium (BK(Ca)) channel in intact HCASMC. In contrast, PGE(2) had no direct effect on channels in cell-free patches, indicating involvement of a soluble second messenger. Enzyme immunoassay demonstrated that PGE(2) enhances production of cAMP in HCASMC, but does not increase [cGMP]. Furthermore, forskolin, CPT-cAMP, or CPT-cGMP mimicked the stimulatory effect of PGE(2) on BK(Ca) channel activity. Interestingly, the response to PGE(2) was unaffected by inhibiting the cAMP-dependent protein kinase, but was antagonized by inhibitors of the cGMP-dependent protein kinase (PKG). Furthermore, cAMP-stimulated PKG activity mimicked the effect of PGE(2). These studies suggest a novel PGE(2) action in human arteries: opening of BK(Ca) channels via cAMP cross-activation of PKG in HCASMC. It is proposed that this signaling mechanism may mediate the vasodilatory response to cAMP-dependent agents in the human coronary and other vascular beds. Copyright 2002 S. Karger AG, Basel