Human trabecular meshwork cells express functional serotonin-2A (5HT2A) receptors: role in IOP reduction.
OBJECTIVE
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.
Sharif
Najam A
NA
Ophthalmology Discovery Research, Alcon Research, Ltd., Fort Worth, Texas 76134, USA. naj.sharif@alconlabs.com
Kelly
Curtis R
CR
McLaughlin
Marsha
M
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000662:Amphetamines / Q000378:metabolism; D000818:Animals; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D005786:Gene Expression Regulation / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006801:Humans; D007223:Infant; D007295:Inositol Phosphates / Q000378:metabolism; D007429:Intraocular Pressure / Q000502:physiology*; D008252:Macaca fascicularis; D008297:Male; D008875:Middle Aged; D009798:Ocular Hypertension / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D044402:Receptor, Serotonin, 5-HT2A / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017366:Serotonin Receptor Agonists / Q000378:metabolism; D014129:Trabecular Meshwork / Q000166:cytology / Q000378:metabolism*; D014162:Transfection
D000662:Amphetamines; D007295:Inositol Phosphates; D012333:RNA, Messenger; D044402:Receptor, Serotonin, 5-HT2A; D017366:Serotonin Receptor Agonists; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C015952:4-iodo-2,5-dimethoxyphenylisopropylamine; D002118:Calcium