Bombesin-evoked gastrin release and calcium signaling in human antral G cells in culture.

Amplification of mRNA from a human antral cell culture preparation demonstrated the presence of two receptors of the bombesin and gastrin-releasing peptide family, GRPR-1 and BRS-3. Single cell microfluorometry demonstrated that most cells that exhibited bombesin-evoked changes in intracellular Ca2+ concentration were gastrin immunoreactive, indicating that antral G cells express the GRPR subtype. There were two components to the intracellular Ca2+ response: an initial nitrendipine-insensitive mobilization followed by a sustained phase that was inhibited by removal of extracellular Ca2+ and 20 mM caffeine and was partially inhibited by 10 microM nitrendipine. Preexposure of cells to thapsigargin and caffeine prevented the response to bombesin, indicating activation of inositol 1,4,5-trisphosphate (IP3)-sensitive stores. Gastrin release could be partially reversed by removal of extracellular Ca2+ and blockade of L-type voltage-dependent Ca2+ channels, indicating that a component of the secretory response to bombesin was dependent on Ca2+ influx. These data demonstrated that bombesin-stimulated gastrin release from human antral G cells resulted from activation of GRPRs and involved both release of intracellular Ca2+ and influx of extracellular Ca2+ through a combination of L-type voltage-gated and IP3-gated Ca2+ channels.