The properties of smooth muscle cell hyperpolarization produced by acetylcholine (ACh) were investigated in mesenteric arteries isolated from mice. The resting membrane potential of the smooth muscle cells was about -60 mV. When ACh (10 μM) was applied for 1 min, the membrane hyperpolarized with a peak amplitude of about 5 mV which was reached in about 1 min, following which the potential slowly reverted to the resting level over about 7 min following withdrawal of ACh from the superfusate (recovery component). Exposure of the artery to 0.5 mM Ba
2+, an inhibitor of inward rectifier K-channels, depolarized the membrane by about 13 mV, increased the amplitude of the ACh-induced hyperpolarization to about 10 mV, and facilitated the visualization of the recovery component. Indomethacine (10 μM), an inhibitor of cyclooxygenase, inhibited the recovery component and as a consequence reduced the duration of the hyperpolarization. The ACh-induced response was not markedly altered by either N
ω-nitro-L-arginine (10 μM), an inhibitor of nitric oxide (NO) production, or catalase (130 U/ml), a super oxide scavenger. Exogenously applied hydrogen peroxide (H
2O
2, 300 μM) hyperpolarized the membrane by about 5 mV, which was abolished by catalase. These results suggest that in the mouse mesenteric artery, the ACh-induced hyperpolarization has two components, both an indomethacin-sensitive and an indomethacin-insensitive component. The former component may be produced by prostanoids, while the latter may be produced by factors other than NO or H
2O
2. The results also suggested that the inward rectifier K-channels may be important for producing the resting membrane potential, but they may not be the main contributor to the ACh-induced hyperpolarization of smooth muscle cell membranes in the mouse mesenteric artery.
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