Ang II receptors are localized in the ciliary epithelium of the eye. Because aqueous humor secretion is linked to the sodium-driven solute transport by ciliary epithelium, we examined whether Ang II causes a change of cytoplasmic sodium in cultured rabbit nonpigmented ciliary epithelium (NPE). Exposure of cultured NPE cells to Ang II in the concentration range 1 pM - 10 nM caused a dose-dependent rise of cytoplasmic sodium concentration detectable by SBFI fluorescence and also by atomic absorption spectrophotometry. The increase of cytoplasmic sodium was inhibited by the non-selective AT1-AT2 receptor antagonist saralasin (IC50 = 3.7 nM) and the selective AT1 antagonist losartan (IC50 = 0.6 nM) but not by the AT2 antagonist PD 123319. Ang II also caused a dose-dependent increase in the rate of ouabain-sensitive ⁸⁶Rb uptake. The Ang II-induced cytoplasmic sodium increase and ⁸⁶Rb uptake increase was significantly reduced by dimethylamiloride (DMA) (10 µM). Based on this finding, we propose Na-H exchange is stimulated by Ang II. Simultaneously, Ang II appears to inhibit H⁺-ATPase-mediated proton export. Thus Ang II (10 nM) did not alter the baseline cytoplasmic pH (pHi) but reduced pHi in cells that were also exposed to 10 µM DMA. Consistent with the notion of H⁺-ATPase inhibition in Ang II-treated NPE, bafilomycin A₁ (100 nM) (BAF) and Ang II were both observed to suppress the pHi increase that occurs when NPE cells are exposed to a mixture of epinephrine (1 µM) and acetylcholine (10 µM) and the pHi increase elicited by cell depolarization. In ATP hydrolysis measurements, H⁺-ATPase activity (bafilomycin A₁-sensitive ATP hydrolysis) was reduced significantly in cells that had been pretreated 10 min with 10 nM Ang II. In summary, these studies suggest that Ang II causes H⁺-ATPase inhibition and an increase of cytoplasmic sodium due to activation of Na-H exchange.