IOVS Journal of Clinical Investigation
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Investigative Ophthalmology & Visual Science, Vol 29, 1866-1870, Copyright © 1988 by Association for Research in Vision and Ophthalmology

ARTICLES AND REPORTS

The effect of vanadate upon calcium-stimulated ATPase of the rabbit iris-ciliary body

RR Socci and NA Delamere
Department of Ophthalmology, University of Louisville School of Medicine, Kentucky.

In many tissues, the level of cytoplasmic calcium mediates cell function. Since cytoplasmic calcium is often maintained at a low level by active calcium extrusion, we examined whether calcium-stimulated ATPase is present in the rabbit ciliary epithelium. A technique was developed to measure calcium-stimulated ATPase in a partially enriched plasma membrane preparation. The enhancement of Na,K-ATPase activity was used to indicate the enrichment of plasma membrane. Marked stimulation of ATPase activity by calcium was observed over a range of calcium concentrations (10(-8) to 10(-3) M). The calcium concentration necessary to elicit half-maximal ATPase activity was 10(-6) M, which is similar to that reported for other membrane preparations. Calcium- stimulated ATPase activity was significantly inhibited in the presence of low concentrations of sodium orthovanadate. The inhibitory influence of vanadate was examined over a range of vanadate concentrations (10(- 8) to 10(-3) M). The vanadate concentration needed to produce half- maximal inhibition of calcium-stimulated ATPase was 2 X 10(-6) M. These studies show that calcium-stimulated ATPase inhibition can occur, in vitro, at very low levels of vanadate; it is possible that this might contribute to the chain of events which results in the lowering of aqueous humor secretion reported in vanadate-treated rabbits.


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M. B. Wax, I. Saito, T. Tenkova, T. Krupin, B. Becker, N. Nelson, D. Brown, and S. L. Gluck
Vacuolar H+-ATPase in ocular ciliary epithelium
PNAS, June 24, 1997; 94(13): 6752 - 6757.
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