ETB and epidermal growth factor receptor stimulation of wound closure in bovine corneal epithelial cells

To determine if there is a heterogeneous pattern of endothelin (ET) receptor subtype (i.e., ETA and ETB) gene expression in the bovine corneal epithelium (BCE). To determine if ET receptor subtype stimulation increases the effectiveness of epidermal growth factor (EGF) to accelerate wound closure in a primary culture of bovine corneal epithelial cells (BCEC).

In situ hybridization histochemistry was used to characterize ETA and ETB gene expression in the BCE. A wound closure assay evaluated wound healing rates in BCEC after 4 to 7 days in culture. [3H] thymidine incorporation and MTT assay measured proliferation.

ETA gene expression was appreciably higher in the basal cells than in the suprabasal cells, whereas the pattern for ETB was reversed. Epidermal growth factor (5 ng/ml) maximally increased wound closure by 145% above the control. With 5 ng/ml EGF, either 10(-9) M ET-1 or 10(-8) M sarafotoxin-6-c (s-6-c) increased wound closure by an additional 39% (P < 0.001) above that measured with 5 ng/ml EGF alone. BQ123 (10(-7) M) did not alter any of these effects of ET-1 or s-6-c. Epidermal growth factor stimulated wound closure through a selective increase in proliferation. Neither ET-1 nor s-6-c alone had any effect on proliferation or migration.

Both ETA and ETB genes are expressed in BCE. However, in BCEC only, ETB stimulation increases the effectiveness of EGF to stimulate wound closure. This response was caused by an increase in cell migration rather than proliferation because, after treatment with mitomycin C, neither ET-1 nor EGF stimulated wound closure.