Exogenous ATP raises cytoplasmic free calcium in fura‐2 loaded piglet aortic endothelial cells

Abstract

Cultured piglet endothelial cells were grown to confluence on glass coverslips and loaded with the fluorescent Ca²⁺ indicator, fura-2. Using a dual-wavelength excitation fluorescence spectrophotometer it was found that ATP caused a rapid transient elevation in [Ca²⁺]_i in the presence of extracellular calcium which decreased to a maintained elevated level. With no extracellular calcium ATP evoked a similar transient increase which returned to the basal level. Addition of 50 mM K⁺ had no effect on [Ca²⁺]_i or on the effect of ATP on [Ca²⁺]_i in the presence of extracellular Ca²⁺. The data suggest that ATP causes both discharge of calcium from an intracellular pool and influx across the plasma membrane although this is unlikely to be via a voltage-operated channel. ATP stimulated simultaneously the production of PGI₂ to a similar extent in the presence or absence of extracellular calcium. Elevated [Ca²⁺]_i may be an important activation pathway in the endothelial cell.