ENDOTHELIN RECEPTOR-A IS EXPRESSED AND MEDIATES THE [CA2-MUSCLE, CILIARY NONPIGMENTED EPITHELIUM, AND TRABECULAR MESHWORK(](I) MOBILIZATIONOF CELLS IN HUMAN CILIARY SMOOTH)

Purpose. To identify which endothelin receptor subtype is expressed an d is functional in the human ciliary body and trabecular meshwork, tis sues that regulate aqueous humor dynamics. Methods. Immunocytochemistr y was used to characterize the primary culture cells of normal human o cular cells. Endothelin receptor gene expression was probed with rever se transcription of polymerase chain reaction (RT-PCR). Intracellular calcium ([Ca2+](i)) mobilization was measured with video image micros copy using Fura-2AM as a fluorescent probe. Results. Identities of pri mary cultures, human ciliary smooth muscle (HCSM), ciliary nonpigmente d epithelial (HCE), and trabecular meshwork (HTM) cells were confirmed by immunocytochemistry, using cell-specific markers and observing typ ical cell morphologies. The presence of endothelin receptor A (ETA) wa s detected with RT-PCR in all three types of cells. The mRNA phenotype was verified with restriction enzyme BamHI digestion. No ETB receptor subtype expression was detected with RT-PCR under the cell culture co nditions used. The [Ca2+](i) of HCSM cells was increased from 57 +/- 7 nM to 328 +/- 108 nM (n = 23; mean +/- SE; P < 0.05) by 1 nM endothel in-1 (ET-1). In HCE cells, [Ca2+](i) increased from 40 +/- 3 nM to 90 +/- 10 nM (n = 55) (P < 0.001) with the same concentration of ET-1. Si milarly, ET-1 (1 nM) increased the [Ca2+](i) from 51 +/- 6 nM to 185 /- 47 nM (n = 19) (P < 0.001) in the HTM cells. The agonist for ETB, S 6c, had no effect on [Ca2+](i) transients in all three cell types. No ETB receptor expression was detected in these cell types under the exp erimental and culture conditions. Conclusion. ETA receptor is expresse d and is possibly responsible for mediating the signal for [Ca2+](i) m obilization by ET-1 in human ciliary smooth muscle, ciliary nonpigment ed epithelial cells, and trabecular meshwork cells.