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Bradykinin-evoked rises in [Ca2+](i) were measured in fura-2-loaded bovine pulmonary artery endothelial cell monolayers by dual wavelength excitation fluorimetry. In monolayers seeded thinly and grown to confluence, bradykinin, in the presence of external Ca2+, evoked a rise in [Ca2+](i) composed of an initial peak and subsequent oscillating plateau. In the absence of external Ca2+, bradykinin evoked a rise in [Ca2+](i) which then returned to the basal value without oscillating. In monolayers seeded near confluent density, the bradykinin-evoked peak in [Ca2+](i) was followed by a steady plateau which showed no oscillation. The addition of the phorbol ester, phorbol 12,13-dibutyrate, to a monolayer during bradykinin-evoked oscillations abolished the oscillations and lowered [Ca2+](i) partway back toward the basal level. The addition of the protein kinase C inhibitor, H7, did not abolish oscillatory activity, although the frequency of oscillation was reduced. These results indicate that synchronized oscillatory activity can occur in endothelial cell monolayers. It is suggested that these oscillations are dependent on intercellular coupling developed when the cells are grown to confluence and that the mechanism responsible for generating oscillations in [Ca2+](i) requires extracellular Ca2+ and involves protein kinase C.