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From the Laboratory of Membrane Biology, Neuroscience Center, Massachusetts General Hospital, Charlestown, Massachusetts.
PURPOSE. Ion gradients established by NaK-adenosine triphosphatase (ATPase) in the ocular ciliary epithelium (CE) contribute to the production of aqueous humor. Modulation of NaK-ATPase activity in the CE may alter aqueous inflow, aqueous turnover, and intraocular pressure. To understand the role of NaK-ATPase, it is necessary to examine the distribution of NaK-ATPase subunit isoforms within the epithelium.
METHODS. Isoform-specific antibodies and scanning laser confocal microscopy were used to localize NaK-ATPase subunit isoforms in the CE of the mouse and rat.
RESULTS. The nonpigmented epithelium (NPE) expressed 
2 and ß3 at very high
levels on its basolateral surface, and 1 and ß2 at much lower
levels. The pigmented epithelium (PE) expressed 1 and ß1 subunits
on its basolateral surface along its entire length, whereas 3 was
expressed in the pars plana only. The distribution and apparent
expression levels of isoforms were similar for mouse and rat, with only
minor discrepancies, most likely caused by antibody sensitivity.
CONCLUSIONS. The results indicate that sodium pumps in the NPE are primarily
composed of 2 and ß3, whereas those in the PE are 1 and ß1.
This specialization in isoform expression implies that NaK-ATPase has
distinct physiological functions in the two epithelia and that its
activity is likely to be regulated by different
mechanisms.
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