Mechanisms of the inhibitory effects of a phenoxazine compound, 2-amino-4,4α-dihydro-4α-7-dimethyl-3H-phenoxazine-3-one, on the contraction of the smooth muscle of the guinea pig taenia cecum

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To elucidate the mechanisms involved in the relaxing effect of 2-amino-4, 4α-dihydro-4α-7-dimethyl-3H-phenoxazine-3-one (Phx-1) on smooth muscle, we investigated its effects on the contraction of both intact and skinned (cell membrane permeabilized) preparations from the guinea pig taenia cecum. In intact preparations, Phx-1 concentration-dependently suppressed the contraction induced by either acetylcholine (ACh) or high-K^+ with an IC_<50> value estimated at around 100 μM. Similar inhibitory actions of Phx-1 on force were observed in intracellular Ca store depleted preparations. In cell membrane depolarized preparations in the absence of extracellular Ca, however, Phx-1 had little effect on either caffeine- or ACh-induced contractions. In skinned preparations, Phx-1 suppressed Ca^<2+>-induced contractions at concentrations higher than 100 μM. These results suggest that inhibition of smooth muscle contraction by Phx-1 is due mainly to inhibition of Ca^<2+>-influx, although Phx-1 also seems to have direct inhibitory effects on the activities of the contractile apparatus.
日本平滑筋学会の論文