Effects of arterial pH and carbon dioxide on pancreatic exocrine H+/HCO‐3 secretion and secretin‐dependent translocation of cytoplasmic vesicles in pancreatic duct cells
Аннотация:To elucidate why arterial pH and carbon dioxide ( P aco2 ) modify the pancreatic H + / HCO ‐ 3 secretory response to secretin stimulation, experiments were performed on anaesthetized pigs, recording the effects of arterial pH and P aco2 on exocrine H + / HCO ‐ 3 secretion and on morphology of pancreatic duct cells. Duct cells contained numerous cytoplasmic vesicles at secretory rest. Their number more than doubled during elevation of P aco2 from 5.5 to 11.0 kPa. At arterial pH 7.40, maximal secretin stimulation cleared the cytoplasm of duct cells of more than 90% of the vesicles. At high P aco2 , this was accompanied by doubling the basolateral plasma membrane area and a 30% higher secretion rate than at P aco2 5.5 kPa. Lowering arterial pH to 7.0 more than halved the secretin‐induced vesicle clearance of duct‐cell cytoplasm as well as exocrine H + /HCO ‐ 3 secretion and abolished the secretin‐dependent basolateral membrane area changes. Supramaximal secretin stimulation did not reverse the inhibitory effect of severe metabolic acidosis on secretion. It is concluded that P aco2 and arterial pH may modify the secretory response to secretin through determining the incorporation of cytoplasmic vesicle material into the basolateral plasma membrane of duct cells.
