Human trabecular meshwork cells express functional serotonin-2A (5HT2A) receptors: role in IOP reduction

Invest Ophthalmol Vis Sci. 2006 Sep;47(9):4001-10. doi: 10.1167/iovs.06-0062.

Abstract

Purpose: To apply a multidisciplinary approach to the identification and pharmacological characterization of the serotonin (5HT) receptors that mediate functional responses in human trabecular meshwork (h-TM) cells. To correlate in vitro findings with intraocular pressure (IOP) changes in conscious ocular hypertensive cynomolgus monkeys.

Methods: Documented methods were used, including reverse transcription-polymerase chain reaction (RT-PCR), phosphoinositide (PI) turnover, and intracellular Ca2+ ([Ca2+]i) mobilization. IOP was measured using standard applanation pneumatonometry.

Results: h-TM cells expressed robust mRNA signals for 5HT2A and 5HT2B receptors. 5HT and its analogues stimulated PI turnover and [Ca2+]i mobilization in h-TM cells from multiple donors (20/24 donors' TM cells responded). The agonist potencies (EC50) of compounds in mobilizing [Ca2+]i were (nM): 5-methoxy tryptamine, 8 +/- 4; (R)-DOI, 18 +/- 6; alpha-methyl-5HT, 22 +/- 3; 5HT, 40 +/- 7; 5-methoxy-dimethyl tryptamine, 64 +/- 27; and BW-723C86, 1213 +/- 210. These effects were potently blocked by the 5HT2A-receptor-selective antagonist, M-100907 (Ki = 1 +/- 0.3 nM), but weakly by antagonists of 5HT2B and 5HT2C receptors. Only 5HT2 receptor agonists such as (R)-DOI (300 microg lowered IOP 34.4% from baseline of 38.2 mm Hg; P < 0.001) and alpha-methyl-5HT (250 microg lowered IOP 30.8% from baseline of 41.8 mm Hg; P < 0.001) lowered IOP in ocular hypertensive cynomolgus monkeys.

Conclusions: Strong signals for 5HT2A and 5HT2B receptor mRNAs were detected in h-TM cells. The receptors that coupled to PI hydrolysis and [Ca2+]i mobilization in h-TM cells were the 5HT2A receptor subtype, which also significantly lowered IOP in a primate model. These receptors may mediate the ocular hypotensive actions of 5HT2A agonists.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Amphetamines / metabolism
  • Animals
  • CHO Cells
  • Calcium / metabolism
  • Child
  • Child, Preschool
  • Cricetinae
  • Cricetulus
  • Female
  • Gene Expression Regulation / physiology*
  • Guanosine 5'-O-(3-Thiotriphosphate) / metabolism
  • Humans
  • Infant
  • Inositol Phosphates / metabolism
  • Intraocular Pressure / physiology*
  • Macaca fascicularis
  • Male
  • Middle Aged
  • Ocular Hypertension / metabolism*
  • RNA, Messenger / metabolism
  • Receptor, Serotonin, 5-HT2A / genetics*
  • Receptor, Serotonin, 5-HT2A / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Serotonin Receptor Agonists / metabolism
  • Trabecular Meshwork / cytology
  • Trabecular Meshwork / metabolism*
  • Transfection

Substances

  • Amphetamines
  • Inositol Phosphates
  • RNA, Messenger
  • Receptor, Serotonin, 5-HT2A
  • Serotonin Receptor Agonists
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • 4-iodo-2,5-dimethoxyphenylisopropylamine
  • Calcium