THE NK1 RECEPTOR AND ITS PARTICIPATION IN THE SYNERGISTIC ENHANCEMENTOF CORNEAL EPITHELIAL MIGRATION BY SUBSTANCE-P AND INSULIN-LIKE GROWTH-FACTOR-I

1 We have previously shown that substance P (SP) and insulin-like grow th factor-1 (IGF-1) act synergistically to enhance the migration of ra bbit corneal epithelial cells in an organ culture model. The present s tudy was designed to identify the epithelial cell SP receptor that par ticipates in this synergistic effect. 2 Rabbit corneal blocks were inc ubated for 24 h, then the length of the path of epithelial migration w as measured. Reagents tried in the TC-199 culture medium, in the prese nce or absence of IGF-1, were: SP, agonists of tachykinin receptors NK 1, NK2 or NK3 and antagonists of tachykinin receptors NK1 or NK2. 3 Th e binding characteristics of SP receptors were examined in rabbit cult ured corneal epithelial cells by binding assays with [I-125]-SP in the presence or absence of excess unlabelled SP or ligands of NK1, NK2 or NK3 receptors. 4 As was demonstrated previously, SP and IGF-1 stimula ted epithelial migration when they were added to the culture medium to gether, but individually they had no effect. NK1 agonists had the same synergistic effect with IGF-1 as did SP, but the NK2 and NK3 agonists did not. Furthermore, the NK1 antagonist abolished the synergistic ef fect of SP and IGF-1, but the NK2 antagonist had no effect. 5 SP bound specifically to rabbit cultured corneal epithelial cells. The binding affinity was 0.44 nM and there were 2.43 x 10(4) binding sites per ce ll. The NK1 ligand competed, in a dose-dependent fashion, with the bin ding of SP to corneal epithelial cells, but neither the NK2 nor NK3 li gand affected binding.6 We conclude that the SP receptor in rabbit cor neal epithelial cells is NK1 and that this receptor participates in th e synergistic enhancement of corneal epithelial migration by SP and IG F-1. The precise. mechanism(s) of this interaction requires more study . These findings imply that both neural and humoral factors are essent ial for the maintenance and healing of corneal epithelium.