抄録
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 non-selective cation channels (NSCCs). Here we examined effects of YM-254890, a Gq/11-specific inhibitor, on contraction, NSCC currents and [Ca2+]i elevation induced by carbachol (CCh). Methods Bovine eyes were obtained from a local slaughterhouse. Tension was recorded isometrically from excised ciliary muscle bundles. For the other experiments, myocytes were enzymatically isolated and cultured for 1-5 days. Whole-cell currents were recorded by voltage clamp. The intracellular Ca2+ concentration [Ca2+]i was recorded using the Fluo-4 indicator. AlexaFluor-conjugated antibodies were used in the immunostaining. 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 μM) evoked a NSCC current as well as an elevation of [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 Like its phasic component, the tonic component of the contraction of bovine ciliary muscle is probably under control of signals conveyed from M3R through a Gq/11-linked mechanism which communicates in some manner with NSCCs. [J Physiol Sci. 2008;58 Suppl:S80]
