Physiological Properties of the Normal Lens.
Mathias, R. T., J. L. Rae, and G. J. Baldo.
Dept. of Physiology and Biphysics, State University of New York, Stony
Brook, New York; and Dept. of Physiology and Biophysics, Mayo Foundation,
Rochester, New York.
APStracts 2:0040P, 1996.
ABSTRACT
The lens is an avascular organ suspended between the aqueous and vitreous
humors of the eye. The cellular structure is symmetric about an axis passing
through its anterior and posterior poles but asymmetric about a plane passing
through its equator. Because of its asymmetric structure, the lens has
historically been assumed to perform transport between the aqueous and
vitreous humors. Indeed, when anterior and posterior surfaces were isolated in
an Ussing chamber, a translens current was measured. However, in the eye, the
two surfaces are not isolated. The vibrating probe technique showed the
current densities at the surface of a free-standing lens were surprisingly
large, about an order of magnitude greater than measured in an Ussing chamber,
and were not directed across the lens. Rather, they were inward in the region
of either anterior or posterior pole and outward at the equator. This
circulating current is the most dramatic physiological property of a normal
lens. We believe it is essential to maintain clarity; hence, this review
focuses on factors likely to drive and direct it. We review properties and
spatial distribution of lens Na[sup]+[r]/K[sup]+[r] pumps, ion channels, and
gap junctions. Based on these data, we propose a model in which the difference
in electromotive potential of surface versus interior cell membranes drives
the current, whereas the distribution of gap junctions directs the current in
the observed pattern. Although this model is clearly too simple, it appears to
quantitatively predict observed currents. However, the model also predicts
fluid will move in the same pattern as ionic current. We therefore speculate
that the physiological role of the current is to create an internal
circulatory system for the avascular lens.
APS Manuscript Number P20-6.
Article publication pending January 1997, Physiological Reviews.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 November 1996