THE PATHWAYS REGULATING ACID-SECRETION - THE VIEW FROM THE ISOLATED CELL

Although many aspects of the regulation of acid secretion at the cellu lar level among different species remains controversial, certain conce pts have emerged that span the differences between species, model syst ems and investigators. The paracrine, endocrine, neural and autocrine pathways mediate acid secretion by acting both directly on the parieta l cell and indirectly via modulation of mucosal paracrine cell functio n. Studies with cells isolated from the acid secreting canine oxyntic mucosa indicate that gastrin and cholinergic receptors are present on parietal cells, somatostatin cells, and the histamine-enterochromaffin -like cell (ECL). Subtypes of these receptors are clearly important; t he gastrin receptor on the ECL cell and parietal cell are ''B'' type C CK/gastrin receptors, whereas the receptor on the somatostatin cell is an A type CCK receptor. From the vantage point of studies in the cani ne oxyntic mucosa, the challenge is no longer to determine whether par ietal, histamine or somatostatin cells have gastrin or muscarinic rece ptors but to establish the physiologic relevance of the specific actio ns (secretory, trophic or differentiative) of these receptor subtypes. Furthermore, the mechanisms integrating these paracrine, exocrine and neural elements require elucidation.