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Y. Zhang, Q. Xie, J.A. Bonanno; Capacitative Calcium Entry Enhances Apical HCO3- Permeability in Bovine Corneal Endothelium . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3448.
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Purpose: In corneal endothelial cells, apical HCO3- permeability can be enhanced by increasing intracellular calcium concentration via either activation of purinergic receptor or inhibition of the sarcoendoplasmic reticulum calcium-ATPase ( SERCA ).In this study we determined whether there is any selective requirement for capacitative calcium entry ( CCE ) or intracellular calcium release for enhancement of apical HCO3- permeability. Methods: Primary cultured bovine corneal endothelial cells were used in all the assays. 2’7’-bis)2-carboxyethyl)-5(6)-carboxyfluorescein acetixymethyl ester ( BCECF-AM ) and Fura-2 acetoxymethyl ester were used in the measurements of intracellular pH and calcium concentration, respectively. Results: The experiments found that both the purinergic agonist ATPγS and the SERCA inhibitor cyclopiazonic acid, which mobilize calcium and lead to CCE, both increased apical HCO3- permeability in control ringer by 79%±12% and 95%±24%, respectively [ IOVS 2002 Apr; 43(4): 1146-53 ], but not in the ringer absent of extracellular calcium. The addition of the CCE blocker 2-aminoethoxydiphenyl borate ( 2-APB ) to control ringer inhibited the enhancement of apical HCO3- permeability by The SERCA inhibitor thapsigargin. Conclusions: These results suggest that CCE is directly responsible for enhanced apical HCO3- permeability in bovine corneal endothelium during purinergic stimulation.
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