Immunocytochemical localization of NaK-ATPase isoforms in the rat and mouse ocular ciliary epithelium.

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 alpha2 and beta3 at very high levels on its basolateral surface, and alpha1 and beta2 at much lower levels. The pigmented epithelium (PE) expressed alpha1 and beta1 subunits on its basolateral surface along its entire length, whereas alpha3 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 alpha2 and beta3, whereas those in the PE are alpha1 and beta1. 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.