EPOXYEICOSATRIENOIC ACIDS ACTIVATE K-MUSCLE THROUGH A GUANINE-NUCLEOTIDE-BINDING PROTEIN( CHANNELS IN CORONARY SMOOTH)

Epoxyeicosatrienoic acids (EETs) are endothelium-derived arachidonic a cid metabolites of cytochrome P450. They dilate coronary arteries, ope n K+ channels, and hyperpolarize vascular smooth muscles. However, the mechanisms of these smooth muscle actions remain unknown. This study examined the effects of EETs on the large-conductance Ca2+-activated K + channel (K-Ca) in smooth muscle cells of small bovine coronary arter ies. In cell-attached patch-clamp experiments, 11,12-EET produced a 0. 5- to 10-fold increase in the activity of the K-Ca channels when added in concentrations of 1, 10, and 100 nmol/L. In the inside-out excised membrane patch mode, 11,12-EET was without effect on the activity of the K-Ca channel unless GTP (0.5 mmol/L) or GTP and ATP (1 mmol/L) wer e added to the bath solution. In the presence of GTP and ATP, the incr ease in the K-Ca channel activity with 11,12-EET in inside-out patches was comparable to that in cell-attached patches. This effect of 11,12 -EET in inside-out patches was blocked by the addition of GDP-P-S (100 mu mol/L). In outside-out patches, 11,12-EET also increased the K-Ca channel activity when GTP and ATP were added to the pipette solution. The addition of a specific anti-G(S) alpha antibody (100 nmol/L) in th e pipette solution completely blocked the activation of the K-Ca chann els induced by 11,12-EET. An anti-G beta gamma or anti-G(i) alpha anti body was without effect. We conclude that 11,12-EET activates the K-Ca channels by a G(S) alpha-mediated mechanism. This mechanism contribut es to the effects of EETs as endothelium-derived hyperpolarizing facto rs to hyperpolarize and relax arterial smooth muscle.