Effects of Extracellular Acidification on Intracellular pH and ATP-Induced Calcium Mobilization in Rabbit Lens Epithelial Cells

Effects of extracellular acidification on intracellular pH (pHi) and ATP-induced calcium mobilization were investigated in rabbit lens epithelial cells. Primary-cultured lens epithelial cells of Japanese white rabbits were used. Intracellular calcium ([Ca]i) and pHi were measured by using fluorescent dyes, fura-2 acetoxymethylester (fura-2 AM) and 2',7'-bis (carboxyethyl)-5,6-carboxyfluorescein acetoxymethylester (BCECF AM), respectively. The addition of 10 μmol/L ATP produced an initial peak followed by a sustained increase in [Ca]i in a standard artificial aqueous humor at extracellular pH (pHo) 7.40. The initial peak was abolished by pretreatment with 1 μmol/L thapsigargin, whereas the sustained increase was attenuated in a Ca2+-free solution or by pretreatment with 100 μmol/L verapamil. Acidification of the pHo from 7.40 to 6.80 decreased the pHi from 7.21 to 7.03, and enhanced both the initial peak and sustained increase in [Ca]i. These results suggest that acidification of pHo significantly affects the pHi and modifies the ATP-induced [Ca]i transient in rabbit lens epithelial cells.