To address mechanoreceptive roles of trigeminal ganglion (TG) nerve endings in the inner walls of rat anterior eye chambers, we investigated the mechanotransduction process and mechanosensitive (MS) channel on somata of TG neurons innervating this area in vitro. Rat TG neurons innervating inner walls of anterior chambers were labeled by anterior chamber injection of 1,1'-dilinoleyl-3,3,3',3'-tetramethylindocarbocyanine, 4-chlorobenzenesulfonate (FAST DiI). The neuronal cell bodies were voltage clamped using a whole cell patch-clamp technique, while it was deformed by ejection of bath solution to verify mechanotransduction. Immunofluorescence staining was performed on sections of TG ganglia to determine the specific MS channel proteins. Mechanical stimuli induced MS currents in 55 out of 96 FAST DiI-labeled TG neurons. The MS currents exhibited mechanical intensity-dependent and clamp voltage-dependent characteristics. Mechanical stimulation further enhanced the membrane potential and increased the frequency of action potentials. Transient receptor potential ankyrin 1 (TRPA1), TRP vanilloid 4 (TRPV4), acid-sensing ion channel (ASIC) 2 and ASIC3 channel proteins were expressed in FAST DiI-labeled TG neurons. The inhibitory effect of HC-030031, a specific inhibitor of TRPA1, on MS currents demonstrated that TRPA1 was an essential MS channel protein. Taken together, our results show that mechanical stimuli induce MS currents via MS channels such as TRPA1 to trigger mechanotransduction in TG neurons innervating inner walls of anterior chambers. Our results indicate the existence of mechanoreceptive TG nerve endings in inner walls of anterior chambers. Whether the mechanoreceptive TG nerve endings play a role in intraocular pressure sensation warrants further investigation.

Citation: Ling Y, Hu Z, Meng Q, Fang P, Liu H. Bimatoprost increases mechanosensitivity of trigeminal ganglion neurons innervating the inner walls of rat anterior chambers via activation of TRPA1. Invest Ophthalmol Vis Sci. 2016;57:567-576. DOI:10.1167/ iovs.15-18108 PURPOSE. Our previous study found that some trigeminal ganglion (TG) nerve endings in the inner walls of rat anterior chambers were mechanosensitive, and transient receptor potential ankyrin 1 (TRPA1) was an essential mechanosensitive channel in the membrane. To address the effect of bimatoprost on the mechanosensitive TG nerve endings in the inner walls of rat anterior chambers, we investigated its effect on their cell bodies in vitro.METHODS. Rat TG neurons innervating the inner walls of the anterior chambers were labeled by anterior chamber injection of 1,1 0 -dilinoleyl-3,3,3 0 ,3 0 -tetramethylindocarbocyanine, 4-chlorobenzenesulfonate (FAST DiI). Calcium imaging and whole cell patch clamp were used on neuronal cell bodies to detect the activation effect of TRPA1 channels. Whole cell patch clamp was performed to record the currents induced by drugs and mechanical stimulation.Mechanical stimulation was applied to the neurons by buffer ejection. RESULTS. Bimatoprost mimicked the effect of TRPA1 agonists, allyl isothiocyanate (AITC), and (R)-(þ)- CONCLUSIONS.Our results indicate that bimatoprost is a novel agonist of TRPA1, and it can enhance mechanosensitivity of TG nerve endings in the inner walls of anterior eye chambers via TRPA1 activation in rats.Keywords: intraocular pressure, mechanosensitive channel, trigeminal ganglion, transient receptor potential ankyrin 1, bimatoprost L atanoprost, travoprost, and bimatoprost are three efficacious prostanoid analogs used for the treatment of glaucoma. Their effects on aqueous humor outflow are similar. Despite the well-established efficacy of these drugs on intraocular pressure (IOP), the mechanism underlying the hypotensive effect is not fully understood. Latanoprost and travoprost are prodrugs of prostaglandin (PG) FP receptor agonists. A well-studied mechanism for their enhancement of aqueous outflow is the regulation of matrix metalloproteinases and remodeling of extracellular matrix via FP receptor activation.1 However, experimental and clinical evidence suggests that bimatoprost and prostanoid FP receptor agonists stimulate different receptor populations.2-4 Studies performed on a wide array of receptors, ion channels, and transporters have demonstrated that bimatoprost does not meaningfully interact with adrenergic, cholinergic, cannabinoid, dopaminergic, or any of the known prostaglandin receptors, indicating that these receptors are not involved in the mediation of bimatoprost-induced responses.2-4 It has been shown that 17-phenyl prostaglandin F2alpha (PGF2a), an acid hydrolysis product of bimatoprost, is found in the aqueous humor after topical application of bimatoprost in humans.5 Based on the finding that 17-phenyl PGF2a is a potent FP prostanoid receptor agonist, it was proposed t...