December 1988
Volume 29, Issue 12
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Articles  |   December 1988
The effect of vanadate upon calcium-stimulated ATPase of the rabbit iris-ciliary body.
Author Affiliations
  • R R Socci
    Department of Ophthalmology, University of Louisville School of Medicine, Kentucky.
  • N A Delamere
    Department of Ophthalmology, University of Louisville School of Medicine, Kentucky.
Investigative Ophthalmology & Visual Science December 1988, Vol.29, 1866-1870. doi:https://doi.org/
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      R R Socci, N A Delamere; The effect of vanadate upon calcium-stimulated ATPase of the rabbit iris-ciliary body.. Invest. Ophthalmol. Vis. Sci. 1988;29(12):1866-1870. doi: https://doi.org/.

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Abstract

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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