Direct measurement of acid efflux from isolated guinea pig pancreatic ducts.
OBJECTIVE
The current studies used the technique of microphysiometry to directly determine the effects of stimulators and inhibitors of pancreatic duct secretion on acid efflux from isolated pancreatic ducts.


METHODS
Main and interlobular ducts were isolated from guinea pig pancreata by collagenase digestion and manual selection. Segments were placed in the chambers of a microphysiometer, which uses a silicon chip-based, light-addressable potentiometric sensor to determine the proton concentration in the superfusing solution. Isolated ducts were superfused with a low buffer capacity Ringer's solution at 37 degrees C and the extracellular acidification rate (EAR) was determined by computer-directed protocols.


RESULTS
A survey of potential agonists demonstrated that both secretin and the cholinomimetic, carbachol, dramatically increased EAR, with EC50 of 3 nmol/L and 0.6 mumol/L, respectively. The changes in EAR induced by both secretagogues were rapid, peaking within 4-6 minutes, and then declining to a level below the peak but above basal EAR. The enhanced EAR was maintained for at least 30 minutes in the presence of either secretagogue. More modest increases in EAR were evoked by bombesin, substance P, and vasoactive intestinal peptide (VIP). Cholecystokinin and isoproterenol caused no significant change in pancreatic duct EAR. A combination of amiloride and bafilomycin A1, inhibitors, respectively, of Na/H exchange and of vacuolar type H-ATPase activity, caused a dramatic drop in EAR but did not fully inhibit the increase in EAR elicited by carbachol, suggesting that other mechanisms may contribute to agonist-stimulated EAR of pancreatic ducts.


CONCLUSIONS
Thus, the results support the use of microphysiometry as a tool to study pancreatic duct physiology and in particular a method to measure acid efflux from the serosal surface.
Hootman
Seth R
SR
Department of Physiology, Michigan State University, East Lansing 48824-3320, USA.
Hobbs
Errett C
EC
Luckie
Douglas B
DB
D000143:Acids / Q000378:metabolism*; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D004232:Diuretics / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D005765:Gastrointestinal Agents / Q000494:pharmacology; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D018942:Macrolides / Q000494:pharmacology; D008297:Male; D046208:Microchip Analytical Procedures; D008991:Monitoring, Physiologic / Q000295:instrumentation* / Q000379:methods; D010183:Pancreatic Ducts / Q000187:drug effects / Q000378:metabolism*; D012633:Secretin / Q000494:pharmacology
D000143:Acids; D018679:Cholinergic Agonists; D004232:Diuretics; D004791:Enzyme Inhibitors; D005765:Gastrointestinal Agents; D018942:Macrolides; D012633:Secretin; D000584:Amiloride; C040929:bafilomycin A1; D002217:Carbachol