The gastrin-containing G cells, unlike most other endocrine cells which are localized in compact glands, are interspersed among many other cell types in the basal half of the mammalian antral mucosa. It is primarily for this reason that investigators have been unable to isolate G cells and study their properties under controlled in vitro conditions. As a result, all of our information on the cellular mechanisms regulating gastrin secretion and biosynthesis has been limited to in vivo experimentation. We have recently developed a method which purifies G cells 60-100 fold from the antral mucosa of rats. The resulting cell preparation contains 20-30% G cells, which appear viable under electron microscopy and functionally respond to in vivo stimulants of gastrin release. In this proposal, we plan to study the cellular and molecular events involved in stimulus-secretion coupling of gastrin release in this enriched fraction of G cells. The major questions which will be investigated are: 1) Which of the established in vivo gastrin secretory stimulants (i.e. proteins, amino acids, acetylcholine, epinephrine, bombesin) stimulate gastrin secretion and biosynthesis in vivo? 2) Which of the established in vivo gastrin secretory inhibitors (i.e. secretin, glucagon, GIP, calcitonin, somatostatin) inhibit gastrin secretion and biosynthesis in vitro? 3) What is the initial signal for gastrin secretion and/or biosynthesis: the binding of the stimulant to surface membrane receptors, the transport of the stimulant into the cell, or its metabolic degradation? 4) What is the relationship between gastrin secretion and biosynthesis? 5) Is gastrin release or biosynthesis directly regulated or modulated by the intracellular concentration of calcium or cyclic nucleotides? and 6) What factors regulate G cell replication? We feel that the experiments described in this proposal will provide answers to many ot these questions which are basic to understanding the cellular properties of normal G cells. In addition, this information will be needed to understand the molecular basis of certain diseases such as pernicious anemia, Zollinger-Ellison syndrome and duodenal ulcer disease which are associated with abnormal G cell function.