Chloride dependent intracellular pH effects of external ATP in cultured human non-pigmented ciliary body epithelium.

PURPOSE: To examine the effects of extracellular adenosine 5-triphosphate (ATP) on intracellular pH ([pH](i)) in cultured human non-pigmented ciliary body epithelium (HNPE).

METHODS: Intracellular pH was measured using spectrofluorescence video microscopy in isolated HNPE cells loaded with the cell-permeable acetoxymethyl ester form of the fluorescent probe BCECF.

RESULTS: In 5%CO(2)/HCO(3)(-) buffered Ringer's the resting [pH](i) was 7.25 +/- 0.006 (mean +/- SEM). Application of 10 microM ATP significantly decreased [pH](i) to 7.00 +/- 0.007 (P < 10(-5), n = 14). In the presence of 1 mM suramin, a P(2) receptor inhibitor, this process was significantly blocked. This [pH](i) effect required the presence of Cl(-) and was significantly inhibited by 0.1 mM diisothiocyanatostilbene-2-2'-disulfonic acid or acetazolamide (500 microM), indicating the involvement of a Cl(-)/HCO(3)( +) exchange mechanism. This response exhibited little dependence on external Na(+) and remained unaffected by the addition of the Na(+)/H( +) exchanger inhibitor amiloride (1 mM). Clamping intracellular calcium levels by incubation in the cell permeable calcium chelator, the acetoxymethyl ester form of BAPTA (100 microM) in low extracellular calcium solution (pCa9) did not affect the ATP-induced [pH](i) signal. In addition, the vacuolar H(+)-ATPase (V-ATPase) inhibitor, bafilomycin A(1) (1 microM), failed to alter the [pH](i) transient.

CONCLUSION: We have demonstrated that extracellular ATP leads to a sustained increase in [H(+)](i) in HNPE cells via a purinergic receptor activated pathway which is independent of the intracellular calcium signaling system. This study demonstrates that the ATP induced [pH]( i) transient is mediated through an upregulation in Cl(-)/HCO( 3)(-) exchange across the plasmamembrane in HNPE cells.