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Department of Physiology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
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 µM 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.
gastrin-releasing peptide; calcium imaging; nitrendipine; calcium-sensing receptor
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