Electron probe X-ray microanalysis of rabbit ciliary epithelium

Rabbit iris-ciliary bodies were preincubated in control and experimental Ringer's solutions before quick freezing, cryosectioning, dehydration and electron probe X-ray microanalysis. After preincubation in a baseline bicarbonate-free Cl- Ringer's solution, the ciliary epithelial intracellular Na+, K+ and Cl- concentrations were estimated to be 15 +/- 3, 162 +/- 14 and 46 +/- 5 mmol kg-1 intracellular water, respectively. The water and elemental Na, K, Cl and P contents were similar in the non-pigmented (NPE) and pigmented (PE) ciliary epithelial cells. As expected, inhibition of the Na,K-exchange pump by preincubation with ouabain markedly increased the intracellular Na content, and markedly reduced the intracellular K content, verifying the validity of the experimental analysis. The Cl- channels of the NPE cells likely play a critical role in determining the rate of aqueous humor formation. Therefore, we have examined the effects of altering Cl- transport on the intracellular composition in this initial microprobe study of the ciliary epithelium. As expected, exposure to bicarbonate increased the intracellular Cl and water contents. Replacement of external Cl- by NO3- was twice as effective as replacement by gluconate in leaching Cl- out of the intracellular compartment. An unexpected finding was that NO3- replacement of internal Cl- substantially increased the intracellular Na and decreased the intracellular K content, possibly by stabilizing the Na,K-pump in the E1P form and inhibiting enzyme activity.