The project emphasizes the importance of the transport function of the antiporter Na, K-ATPase in maintaining ion homeostasis (Na+ and K+) in the whole lens. The fibers have Na,K-ATPase but the enzyme appears to be inactive save for those newly developed cortical fibers.
AIM 1 : determine if the lens epithelial cells synthesize new Na,K-ATPase by following labeled methionine incorporation into the transporter, determine if inhibition of protein synthesis or actinomycin D blocks the purported turnover.
AIM 2 Determine if the epithelium D blocks the purported turnover.
AIM 2 Determine if the epithelium selectively upregulates the Na,K-ATPase alpha 2 isoform thus increasing the pump activity. The up-regulation is though to be a physiological response to compromised permeability found in older lenses.
Aim 3 : Determine if depolarization triggers increased Na-K- ATPase a2 expression. Determine if depolarization triggers increased Na,K-ATPase a2 expression. Determine if the a2 isoform is insensitive to pump inhibition by increased [Ca]. The PI feels that this may be explained by the lack of a tyrosine phosphorylation site on the a2 isoform. Determine the extent to which the a2 isoform increases with age in human lenses - based on the view tht ionic changes accompany aging in the lens. Determine if isoform change in fibers occurs whenrat lens epithelial cells are induced to differentiate following exposure to fibroblast growth factor. Since fibers have low Na,K- ATPase activity, investigate what inactivtes Na,K-ATPase in the fibers with specific emphasis on possible tyrosine phosphorylation of Na,K- ATPase a1 protein. Determine if slow turnover of Na,K-ATPase in the fibers makes the enzyme susceptible tooxidative modification.
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