Intracellular calcium ‘signatures’ evoked by different agonists in isolated bovine aortic endothelial cells

Abstract

Agonist induced increases in intracellular free calcium, [Ca 2+] i, were measured in single Fura-2 loaded bovine aortic endothelial (BAE) cells by dual wavelength microspectrofluorimetry. Low doses of ATP (< 10 μM) induced complex changes in [Ca 2+] i. These changes usually consisted of a large initial transient peak with subsequent fluctuations superimposed upon a maintained rise in [Ca 2+] i. Higher doses of ATP (> 50 μM) produced much simpler biphasic increases in [Ca 2+] i in individual cells. Acetylcholine and bradykinin also elicited increases in [Ca 2+] i in single cells in confluent monolayers of endothelial cells. However, only acetylcholine produced complex fluctuations. High doses of acetylcholine evoked simple rises in [Ca 2+] i similar to those seen with high doses of ATP. In contrast, bradykinin evoked relatively simple rises in [Ca 2+] i at all doses used. These results indicate that the mechanisms responsible for generating agonist induced increases in [Ca 2+] i in BAE cells are not homogeneous. ATP and acetylcholine produced more complex Ca 2+ changes or ‘signatures’ in single confluent bovine aortic endothelial cells than bradykinin. All three agonists appeared to release Ca 2+ from intracellular stores as well as stimulating Ca 2+ influx. The possible mechanisms underlying these phenomena are discussed.