抄録
In the ciliary muscle, a smooth muscle under parasympathetic control, contraction is initiated by stimulation of muscarinic receptors of M3subtype. It is established that the initial phasic component of the contraction is triggered by Ca2+ release from intracellular stores mediated by Gq-linked signalling pathway. The tonic component is also known to be highly dependent on Ca2+, but Ca2+ is now provided by influx through receptor-operated cation channels rather than by release from stores [Takai et al.(2005) J Physol 559, 899-922]. However, little is known about the signalling mechanism involved in this Ca2+ influx. Here we have examined effects of YM-254890, a putative specific Gq inhibitor on contraction and [Ca2+]i elevation induced by carbachol (CCh). For mechanical experiments ciliary muscle bundles dissected from bovine eyes were vertically mounted in an organ bath continuously perfused with normal saline, and isometric tension was recorded using a U-gauge transducer. Bath application of 2 μM-CCh caused a contraction. Both phasic and tonic components of this response were abolished by YM-254890 (3-10 μM). Using a Fluo-4 fluorescence method, we observed that CCh (10 μM) induced an elevation of the [Ca2+]i in dispersed bovine ciliary muscle cells. Both initial phase and sustained phase of this response were also abrogated by YM-254890 (3-10 μM). Gq appears to be critically involved in Ca2+ mobilization in tonic as well as phasic component of the contraction of bovine ciliary muscle. [J Physiol Sci. 2006;56 Suppl:S160]
