Effects of chloride channel blockers on hypoxic injury in rat proximal tubules. These studies examined the pathways and consequences of chloride uptake into proximal tubule cells during in vitro hypoxia. The chloride channel blocker diphenylamine-2-carboxylate (DPC) markedly reduced the degree of hypoxia-induced membrane damage as measured by the release of lactate dehydrogenase (LDH). DPC reduced the release of LDH from hypoxic tubules from 38 ± 2.7% to 16 ± 1.7% after 30 minutes of hypoxia (P < 0.001, N = 16) and also reduced ³⁶Cl⁻ uptake by hypoxic tubules. The reduction in LDH release was not associated with better preservation of cell ATP content or with protection against hypoxia-induced DNA damage. Other Cl⁻ channel blockers, such as niflumic acid, 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) and 2-[(2-cyclopentyl-6,7-dichloro-2,3-dihyrdo-2-methyl-1-oxo-1H-inden-5-yl)oxy] acetic acid (IAA-94) provided even greater protection than DPC and were as effective as 2 mM glycine. The Cl⁻ channel blockers appear to act late in the course of hypoxic injury since DNA damage, an early manifestation of injury, is not prevented by the blockers and since addition of the Cl⁻ channel blocker after the hypoxic injury has begun reduces further membrane damage. These results support the conclusion that transport through Cl⁻ channels contributes to hypoxic cell injury in proximal tubular cells.