2. Academic Validation
  3. Myopia-Inhibiting Concentrations of Muscarinic Receptor Antagonists Block Activation of Alpha2A-Adrenoceptors In Vitro

Myopia-Inhibiting Concentrations of Muscarinic Receptor Antagonists Block Activation of Alpha2A-Adrenoceptors In Vitro

  • Invest Ophthalmol Vis Sci. 2018 Jun 1;59(7):2778-2791. doi: 10.1167/iovs.17-22562.
Brittany J Carr 1 2 3 4,  Koichiro Mihara 3 5,  Rithwik Ramachandran 3 5 6,  Mahmoud Saifeddine 3 5,  Neil M Nathanson 7,  William K Stell 1 2 8,  Morley D Hollenberg 3 5 9
Affiliations

Affiliations

  • 1 Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
  • 2 Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
  • 3 Inflammation Research Network-Snyder Institute for Chronic Diseases, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
  • 4 Department of Neuroscience, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
  • 5 Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
  • 6 Department of Physiology and Pharmacology, Western University, London, Ontario, Canada.
  • 7 Department of Pharmacology, University of Washington, Seattle, Washington, United States.
  • 8 Department of Cell Biology and Anatomy, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
  • 9 Department of Medicine, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
PMID: 29860464 DOI: 10.1167/iovs.17-22562
Abstract

Purpose: Myopia is a refractive disorder that degrades vision. It can be treated with atropine, a Muscarinic Acetylcholine Receptor (mAChR) antagonist, but the mechanism is unknown. Atropine may block α-adrenoceptors at concentrations ≥0.1 mM, and another potent myopia-inhibiting ligand, mamba toxin-3 (MT3), binds equally well to human mAChR M4 and α1A- and α2A-adrenoceptors. We hypothesized that mAChR antagonists could inhibit myopia via α2A-adrenoceptors, rather than mAChR M4.

Methods: Human mAChR M4 (M4), chicken mAChR M4 (cM4), or human α2A-adrenergic receptor (hADRA2A) clones were cotransfected with CRE/promoter-luciferase (CRE-Luc; agonist-induced luminescence) and Renilla luciferase (RLuc; normalizing control) into human cells. Inhibition of normalized agonist-induced luminescence by antagonists (ATR: atropine; MT3; HIM: himbacine; PRZ: pirenzepine; TRP: tropicamide; OXY: oxyphenonium; QNB: 3-quinuclidinyl benzilate; DIC: dicyclomine; MEP: mepenzolate) was measured using the Dual-Glo Luciferase Assay System.

Results: Relative inhibitory potencies of mAChR antagonists at mAChR M4/cM4, from most to least potent, were QNB > OXY ≥ ATR > MEP > HIM > DIC > PRZ > TRP. MT3 was 56× less potent at cM4 than at M4. Relative potencies of mAChR antagonists at hADRA2A, from most to least potent, were MT3 > HIM > ATR > OXY > PRZ > TRP > QNB > MEP; DIC did not antagonize.

Conclusions: Muscarinic antagonists block hADRA2A signaling at concentrations comparable to those used to inhibit chick myopia (≥0.1 mM) in vivo. Relative potencies at hADRA2A, but not M4/cM4, correlate with reported abilities to inhibit chick form-deprivation myopia. mAChR antagonists might inhibit myopia via α2-adrenoceptors, instead of through the mAChR M4/cM4 receptor subtype.

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