Abstract
To elucidate the mechanisms of relaxing effect of 2-Amino-4,4 α-dihydro-4 α-7-dimethyl-3H-phenoxazine-3-one (Phx-1) on the smooth muscle preparations, we investigated Phx-1 effects on the contraction of both intact and skinned (cell membrane peremeabilised) preparations from guinea pig taenia In intact preparations, Phx-1 dose dependently suppressed either the contraction induced by acetylcholine (ACh) or high-K+. Similar force inhibitory actions of Phx were observed in intracellular Ca store depleted preparations. In the cell membrane depolarized preparations in the absence of extra Ca, however, Phx-1 had little effects on the caffeine- or ACh-induced contraction. In skinned preparations, Phx-1 suppressed the Ca2+-induced contraction at only relatively higher concentrations. These results suggested that inhibition of the smooth muscle contraction by Phx-1 was due mainly to inhibition of Ca2+-influx, although Phx-1 seemed to have direct inhibitory effects on the activities of contractile apparatus [J Physiol Sci. 2007;57 Suppl:S96]
