Volume change of the ocular lens during accommodation.

During accommodation, mammalian lenses change shape from a rounder configuration (near focusing) to a flatter one (distance focusing). Thus the lens must have the capacity to change its volume, capsular surface area, or both. Because lens topology is similar to a torus, we developed an approach that allows volume determination from the lens cross-sectional area (CSA). The CSA was obtained from photographs taken perpendicularly to the lenticular anterior-posterior (A-P) axis and computed with software. We calculated the volume of isolated bovine lenses in conditions simulating accommodation by forcing shape changes with a custom-built stretching device in which the ciliary body-zonulae-lens complex (CB-Z-L) was placed. Two measurements were taken (CSA and center of mass) to calculate volume. Mechanically stretching the CB-Z-L increased the equatorial length and decreased the A-P length, CSA, and lens volume. The control parameters were restored when the lenses were stretched and relaxed in an aqueous physiological solution, but not when submerged in oil, a condition with which fluid leaves the lens and does not reenter. This suggests that changes in lens CSA previously observed in humans could have resulted from fluid movement out of the lens. Thus accommodation may involve changes not only in capsular surface but also in volume. Furthermore, we calculated theoretical volume changes during accommodation in models of human lenses using published structural parameters. In conclusion, we suggest that impediments to fluid flow between the aquaporin-rich lens fibers and the lens surface could contribute to the aging-related loss of accommodative power.

pICln can regulate swelling-induced Cl- currents in either layer of rabbit ciliary epithelium.

Swelling-induced Cl- currents were investigated in freshly prepared non-pigmented epithelial (NPE) and pigmented epithelial (PE) cells of the rabbit ciliary body using the whole-cell patch clamp technique. Exposure of both NPE and PE cells to hypotonic stress induced Cl- currents that exhibited outward rectification and were insensitive to Ca+2. We found that swelling-induced Cl- currents in PE cell are observed shortly after isolation. The swelling-induced Cl- current showed little or no inactivation at positive membrane voltages and was sensitive to 100 microM NPPB and 100 microM DIDS. Injection of cRNA encoded rabbit pICln into Xenopus oocytes produced an outwardly rectifying Cl- current displaying features consistent with the swelling-induced Cl- current in epithelium. pICln is ubiquitous in the ciliary epithelium. It participates in the equilibration of short term tonicity alterations, a phenomenon underlying mechanisms with larger and slower amplitudes for aqueous secretion by these cells.