April 2010
Volume 51, Issue 13
ARVO Annual Meeting Abstract  |   April 2010
Endothelin-1 Contracts Bovine Ciliary Smooth Muscle Evoked by Binding Type 1 Receptor Coupled With the Gq/11 Protein
Author Affiliations & Notes
  • N. Ishii
    Asahikawa Medical College, Asahikawashi, Japan
  • M. Miyazu
    Asahikawa Medical College, Asahikawashi, Japan
  • A. Yoshida
    Asahikawa Medical College, Asahikawashi, Japan
  • A. Takai
    Asahikawa Medical College, Asahikawashi, Japan
  • Footnotes
    Commercial Relationships  N. Ishii, None; M. Miyazu, None; A. Yoshida, None; A. Takai, None.
  • Footnotes
    Support  None.
Investigative Ophthalmology & Visual Science April 2010, Vol.51, 991. doi:
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    • Get Citation

      N. Ishii, M. Miyazu, A. Yoshida, A. Takai; Endothelin-1 Contracts Bovine Ciliary Smooth Muscle Evoked by Binding Type 1 Receptor Coupled With the Gq/11 Protein. Invest. Ophthalmol. Vis. Sci. 2010;51(13):991.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose: : To examine the effects of endothelin-1 (ET1) on the contractility of the ciliary muscle whose tonus is regarded as one of the most determinant factors regulating aqueous humor outflow.

Methods: : Isometric tension was recorded in ciliary muscle bundles excised from fresh bovine eyes obtained from a local slaughterhouse. In ciliary myocytes dispersed with collagenase and cultured for 1-5 days, whole-cell currents were recorded by voltage clamp, and the intraocular free Ca2+ concentration [Ca2+]i was monitored using the Fluo-4 fluorophore. Existence and localization of endothelin receptors type A and B (ETRA and ETRB) were examined by RT-PCR and immunofluorescence microscopy.

Results: : ET1 (1-100 nM) evoked contraction in a dose-dependent manner (ED50=6±1 nM; number of experiments, n=4). Like contractions evoked by stimulation of M3¬muscarinic receptor (M3R) by carbachol (CCh; 2 µM), the ET1-evoked contraction showed a strong dependence on extracellular Ca2+ and was completely inhibited by YM-254890 (500 nM; n=4), a Gq/11-specific inhibitor. It was also partially inhibited by Y-27632 (20 µM; n=4), a Rho kinase inhibitor. Unlike CCh-evoked contraction, however, the ET1-evoked contraction had no rapid phasic component and tended to be washed out very slowly. Also the ET1-evoked response exhibited a higher sensitivity to inhibition by Ni2+ (1 mM) compared with CCh-evoked response. ETRA antagonists dose-dependently inhibited the ET1-evoked whereas ETRB antagonists were without effect. In whole-cell voltage clamp experiments ET1 (10-30 nM) showed an (albeit weak) activating effect on two types of non-selective cation channel which are known to be opened upon M3R stimulation. Immunostaining revealed a dense distribution of ETRA in the plasma membrane of ciliary myocytes.

Conclusions: : The present results strongly indicate that ET1, as well as CCh, contracts bovine ciliary muscle by a Gq/11-coupled mechanism. The relatively weak potency of ET1 may suggest that ETRA activated by ET1 interacts with Gq/11 more loosely than does M3R activated by CCh.

Keywords: ciliary muscle • signal transduction: pharmacology/physiology • outflow: ciliary muscle 

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