2-Hydroxypropyl-β-Cyclodextrin Removes All-TransRetinol from Frog Rod Photoreceptors in a Concentration-Dependent Manner

Abstract

To determine whether a nonprotein lipophilic carrier, 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD), can remove all-trans retinol from rod photoreceptor outer segments. All-trans retinol is generated in rod outer segments after light exposure. It is highly insoluble, and its efficient transport across extra- and intracellular aqueous space requires specialized carriers. Experiments were carried out with isolated frog rod photoreceptor cells. The removal of all-trans retinol by different concentrations of this carrier was measured by imaging its fluorescence in single-rod photoreceptors. HP-beta-CD concentrations >0.3 mM significantly increased the rate of all-trans retinol removal. The rate of removal increased linearly with carrier concentration, with a slope of 0.0058 min(-1)/mM. The effectiveness of HP-beta-CD shows that a specialized interaction with the cell membrane is not necessary for the efficient transfer of all-trans retinol between the cell membrane and the carrier. The transfer occurs through a collision-based mechanism, as indicated by the linear increase of the rate of removal with the carrier concentration.