The influence of phenylephrine outward potassium currents in single smooth muscle cells from the rabbit mesenteric artery.
Mistry DK., Garland CJ.
In mesenteric artery smooth muscle cells, depolarizing voltage steps activated outward K+ currents whose amplitude was decreased by about 20% with phenylephrine (1-10 microM: n = 14 cells). Attenuation of outward current was only partly dependent on [Ca2+]i, because it persisted, although reduced, with 10 mM BAPTA in the patch pipette and was abolished in the presence of 3 mM 3,4-diaminopyridine (n = 13). In outside-out patches, phenylephrine did not exert any direct effect on the unitary current amplitude or open probability of large conductance K+ channels. Outward current was significantly increased (>100% in both cases) by 10 mM caffeine, presumably owing to the release of internal Ca2+ stores. With 10 mM BAPTA in the pipette, the only response to caffeine was a small decrease (9 +/- 3.7%, n = 10) in the K+ current. These observations show that a minor effect of phenylephrine is to reduce outward K+ current (probably Kv) in mesenteric cells.