Abstract
In the ciliary muscle, the tonic component of the contraction produced by muscarinic stimulation is highly dependent on Ca2+ provided by influx through receptor-operated cation channels (ROCs). Here we have examined effects of YM-254890, a Gq/11-specific inhibitor, on contraction, ROC currents and [Ca2+]i elevation induced by carbachol (CCh). Methods Bovine eyes were obtained from a local slaughterhouse. Isometric tension was recorded from excised ciliary muscle bundles using a strain-gauge transducer. For the other experiments, ciliary muscle cells were dispersed with collagenase and cultured for 1-5 days. Whole-cell currents were recorded by voltage clamp. The intracellular free Ca2+ [Ca2+]i concentration was recorded using Fluo-4 (Invitrogen) as the indicator. Results In the muscle bundles, superfusion of 2 μM-CCh evoked a sustained contraction. Both phasic and tonic components of this contraction were inhibited by YM-254890 (3-10 μM) in a dose-dependent manner. In the cultured cells, CCh (0.05-10 μM) evoked a ROC current as well as an elevation of the [Ca2+]i. Both initial and sustained phases of these CCh-evoked responses were abrogated by YM-254890 (3-10 μM). Immunostaining revealed a dense distribution of Gq/11 in the vicinity of the cytoplasmic side of the plasma membrane of the cultured cells. Conclusion Gq/11 appears to be critically involved in Ca2+ mobilization in the tonic as well as phasic component of the contraction in the bovine ciliary muscle. [J Physiol Sci. 2007;57 Suppl:S220]
