[HTML][HTML] Regional distribution of Na, K-ATPase activity in porcine lens epithelium

S Tamiya, WL Dean, CA Paterson… - … & visual science, 2003 - iovs.arvojournals.org
S Tamiya, WL Dean, CA Paterson, NA Delamere
Investigative ophthalmology & visual science, 2003iovs.arvojournals.org
purpose. It has been established that Na, K-ATPase activity is higher in lens epithelium than
fibers. However, others have suggested the Na, K-ATPase enzyme may be inactive or
absent in the central 10% of the epithelium. Studies were conducted to measure and
compare Na, K-ATPase specific activity and to examine Na, K-ATPase protein expression in
the anterior and equatorial regions of porcine lens epithelium. methods. Na, K-ATPase
activity was determined by measuring the ouabain-sensitive rate of adenosine triphosphate …
Abstract
purpose. It has been established that Na, K-ATPase activity is higher in lens epithelium than fibers. However, others have suggested the Na, K-ATPase enzyme may be inactive or absent in the central 10% of the epithelium. Studies were conducted to measure and compare Na, K-ATPase specific activity and to examine Na, K-ATPase protein expression in the anterior and equatorial regions of porcine lens epithelium.
methods. Na, K-ATPase activity was determined by measuring the ouabain-sensitive rate of adenosine triphosphate (ATP) hydrolysis. Western blot analysis was used to detect Na, K-ATPase catalytic subunit (α) and glycoprotein subunit (β) protein as well as β-actin which was used as a loading control.
results. Na, K-ATPase specific activity was more than two times higher in the equatorial epithelium than the anterior 50% of the epithelium. However, the abundance of Na, K-ATPase α1 isoform protein was similar in the two regions. Neither the α2 nor α3 Na, K-ATPase isoform could be detected in the anterior or equatorial epithelium, but Na, K-ATPase β1 protein was detected in both regions. In contrast to the observed regional difference in Na, K-ATPase activity, the activity of a different P-type ATPase, plasma membrane Ca-ATPase (PMCA), was not significantly different in the anterior and central epithelium. Western blot analysis indicated the presence of two PMCA isoforms, PMCA2, and PMCA4.
conclusions. Na, K-ATPase activity is significantly higher at the equatorial region of the epithelium compared with the anterior, even though the level of Na, K-ATPase protein is similar in the two regions. It is possible that nonuniform distribution of functional Na, K-ATPase activity contributes to the driving force for circulating solute movement through the lens fiber mass.
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