The effect of vanadate upon calcium-stimulated ATPase of the rabbit iris-ciliary body.
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.
Socci
R R
RR
Department of Ophthalmology, University of Louisville School of Medicine, Kentucky.
Delamere
N A
NA
D000251:Adenosine Triphosphatases / Q000032:analysis* / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002924:Ciliary Body / Q000187:drug effects / Q000201:enzymology*; D004847:Epithelial Cells; D008722:Methods; D011817:Rabbits; D014638:Vanadates / Q000494:pharmacology*
D014638:Vanadates; D000251:Adenosine Triphosphatases; D002118:Calcium