Fluoxetine inhibits K(+) transport pathways (K(+) efflux, Na(+)-K(+)-2Cl(-) cotransport, and Na(+) pump) underlying volume regulation in corneal endothelial cells.

We have studied regulatory volume responses of cultured bovine corneal endothelial cells (CBCEC) using light scattering. We assessed the contributions of fluoxetine (Prozac) and bumetanide-sensitive membrane ion transport pathways to such responses by determining K(+) efflux and influx. Cells swollen by a 20% hypo-osmotic solution underwent a regulatory volume decrease (RVD) response, which after 6 min restored relative cell volume by 98%. Fluoxetine inhibited RVD recovery; 20 microM by 26%, and 50 microM totally. Fluoxetine had a triphasic effect on K(+) efflux; from 20 to 100 microM it inhibited efflux 2-fold, whereas at higher concentrations the efflux first increased to 1.5-fold above the control value, and then decreased again. Cells shrunk by a 20% hyperosmotic solution underwent a regulatory volume increase (RVI) which also after 6 min restored the cell volume by 99%. Fluoxetine inhibited RVI; 20 microM by 25%, and 50 microM completely. Bumetanide (1 microM) inhibited RVI by 43%. In a Cl(-)-free medium, fluoxetine (50-500 microM) progressively inhibited bumetanide-insensitive K(+) influx. The inhibitions of RVI and K(+) influx induced by fluoxetine 20 to 50 microM were similar to those induced by 1 microM bumetanide and by Cl(-)-free medium. A computer simulation suggests that fluoxetine can interact with the selectivity filter of K(+) channels. The data suggest that CBCEC can mediate RVD and RVI in part through increases in K(+) efflux and Na-K-2Cl cotransport (NKCC) activity. Interestingly, the data also suggest that fluoxetine at 20 to 50 microM inhibits NKCC, and at 100-1000 microM inhibits the Na(+) pump. One possible explanation for these findings is that fluoxetine could interact with K(+)-selective sites in K(+) channels, the NKC cotransporter and the Na(+) pump.